BOOK II.

DESCRIPTIVE, PARTICULAR, OR SPECIAL ANATOMY.

Special Anatomy may be defined to be that science, the province of which is to determine the situation, shape, and component parts of the several textures and organs of which the human body consists. In the course of this, however, it is requisite to premise some observations on the external shape of the body, and the different regions into which it has, for the sake of greater precision, been divided.

The external shape of the human body is so well known, that it is superfluous to describe it. Besides its division into right and left halves, anterior and posterior surfaces, it is divided into head, trunk, and extremities. The trunk is subdivided into neck (collum), chest (thorax, pectus), and belly (abdomen). The extremities are subdivided into thoracic or upper, and pelvic, abdominal, or lower.

The shape of the head is ellipsoidal, or oblong spheroidal; the greater diameter being antero-posterior, and the transverse smallest. The neck is cylindrical, spreading out above and below. The shape of the trunk is that of an irregular cylinder, flattened before and behind, broad above, and tapering below the chest, but expanding again at the pelvis. The extremities affect the cylindrical form, inclining to the conical.

These several parts may be still further subdivided. The head is distinguished into two great divisions, the head proper, and the face. The former corresponds to the scalp, and may be divided into coronal, temporal, parietal, and occipital regions. The coronal or syncipital may be reckoned from the anterior margin of the scalp to the site of the anterior fontanelle, or the line named the coronal suture. Behind this to the crown (vertex), and downwards on each side, are the parietal or lateral regions; from the parietal and frontal is the temporal; from the crown to the flexure of the neck is the hind-head or occipital (occiput); from the last point to the level of the shoulders is the cervix; on each side are the lateral regions of the neck; and before is the laryngeal, jugular, or anterior region of the neck (jugulum).

The face consists of the brow, front or forehead (frontis), with the glabella or mesophrion at its base, in the middle, and the eyebrows (supercilia) on each side; the nose (nasus), the upper lip (supralabium), the lower lip (infralabium), the chin (mentum), the cheeks (genea), the chops (buccae), the upper jaw (maxilla), and lower jaw (mandible).

Besides these, it is usual to distinguish the probalium, or the red portion of the lip, upper and lower, as covered by a thin half-cutaneous, half-mucous skin and epidermis.

The chest, besides its distinction into right and left halves, anterior and posterior surfaces, and upper and lower boundaries, may be distinguished into a sternal region in the middle (sternum), a mammary region on each side, an axillary region, a costal region, a hypochondriac region, a scapular region, and a vertebral region.

Several of these regions it is convenient to subdivide in the following manner. The upper anterior region, immediately below the collar-bone, is distinguished as the sub-clavicular region; the space between the breast and the axilla as the extra-mammary region; that between the breast and the sternum as the intra-mammary region; the space below the breasts on each side as the infra-mammary region; the space below the armpit as the sub-axillary region. On the posterior surface of the chest, the space above the spine of the scapula is called the supra-spinal region; that below it the infra-spinal region.

The abdomen may be distinguished into regions in the following manner. The triangular space between the false ribs and navel, commonly named the pit of the stomach, is the epigastric region (serobiculus cordis, epigastrium). Below this, in the centre, is the umbilical (umbilicus), with the iliac region or flanks, (ilia) on each side, and the hypogastric (hypogastrium) below. Behind, on each side of the vertebral column, are the loins, (lumbi).

Next to the abdomen is the pelvis, the posterior lateral parts of which are the buttocks (nates), the anterior, the pubes, and the inferior, the hips or ischiatic regions (ischia), with the perineum in the middle between them.

In the trunk of the body, besides the chest, the abdomen, and the pelvis, it is proper to distinguish the region of the back-bone or spine, extending along the whole length of the trunk from the head to the lower end of the trunk. The spine or spinal region is divided into four subordinate regions; the cervical, the dorsal, the lumbar, and the sacral or sacro-coccygeal.

In each pectoral extremity are recognized the following division; the shoulder (humerus), the armpit (axilla), the arm (brachium), the elbow (cubitus), the fore-arm (ante-brachium), the wrist (carpus), and the hand (manus). The latter is subdivided into the fore-wrist (metacarpus), the fingers (digits), the palm (vola), and the back-hand (thenar).

Each abdominal extremity presents the following separate regions; the haunch (coxæ), the thigh (femur), the knee (genus), the ham (poples), the leg (tibia), of which there is the muscular part or calf (sura), the ankle external and in- Special Anatomy.

The divisional (malleolus externus et internus), the foot (pes), subdivided into the ankle-joint (tarsus), the foot-joint (metatarsus), the toes (digitii pedis), with dorsal or upper surface, and plantar surface or sole (solea).

These divisions, though not so numerous as they have been made by some, are sufficiently so for the purpose of general anatomical description. Where more minute distinction is requisite, it shall be introduced as we proceed.

Descriptive or Special Anatomy includes not only the descriptions of the situations and relations of the different classes of textures in the human body and that of the internal organs, but it comprehends also a particular form of anatomical knowledge necessary to the surgeon. This consists in defining, as accurately as language and measurement can do, the boundaries of the different regions into which the human body may be divided, and ascertaining the positions and relations of all the important parts that are liable to become the seat of local disease and chirurgical operation. To this department the names of Chirurgical Anatomy, Topographical Anatomy, and Anatomy of Regions, are given.

The limits within which the present article must be confined permit not to enter upon this department of Anatomical knowledge. It is sufficient to say, that useful treatises on this subject have been published by Velpeau, Blandin, Edwards; and that in the systems of operative Surgery, especially that by Mr William Fergusson, and the work of Mr Macleish, correct information upon the boundaries and the relative positions of the various regions is communicated.

The stature of the body varies in the two sexes, in individuals, in families, in tribes, and in nations. The Romans, when they first visited Gaul, remarked the gigantic stature of the ancient inhabitants of that country compared with themselves; and, generally speaking, the modern Italians, though by no means a pure or unmixed breed from the ancient stock, are a diminutive race. The Germans, and most of the English and Irish, are rather tall. The inhabitants of Finland are distinguished for their great stature, amidst the dwarfish tribes by which they are surrounded. In general the Europeans are taller than the Asiatics.

The average height of the adult male varies from 5 feet 8 inches to 5 feet 10 or 11 inches, or even to 6 feet. The dimensions of different parts vary according to those of the whole body; but the following measurements of a male of 5 feet 8 inches, and one of 5 feet 11 inches, may communicate some idea of the length of different regions of the body.

| Measurement | Inches | |--------------------------------------------------|--------| | Total height | 69-00 | | Between the tips of the middle fingers, with the arms extended | 65-00 | | From the crown to the pubes | 34-00 | | From the crown to the lower tip of the chin | 9-75 | | From the tip of the chin to the top of the breast | 3-85 | | From the top of the breast to the pit of the stomach | 6-08 | | Between the pit of the stomach and the navel | 6-08 | | Between the navel and top of the pubes | 6-08 | | Between the top of the shoulder and the bend of the elbow | 12-06 | | From the bend of the elbow to the top of the hand | 10-02 | | The hand, from the wrist to tip of middle finger | 7-75 | | Between the top of the thigh inside and the knee inside | 14-06 | | From the knee inside to the sole | 18-05 | | The foot, from the heel to the point of the great toe | 9-75 |

The average height of the female varies from 5 feet 3 inches to 5 feet 5 inches and 5 feet 7 or 8 inches. A woman of 5 feet 10 inches is unusually tall. The length of the different regions is proportionally less than in the male.

The length of the body previous to adult age varies with the period of life. The length of an embryo of three weeks, represented by Soemmerring, is about ¼ of an inch; one of eight weeks is about 1 inch; and one at the end of the fifth month is about 10 inches. According to Burns, however, the length of the fetus in the fifth month does not exceed 6 or 7 inches; in the sixth it is about 8 or 9, in the seventh about 12, and in the eighth about 15 inches. At the period of birth, the average length, according to Roederer, is about 20½ inches.

The only part of the fetus of which it is important to determine the average dimensions at the period of birth is the head. Its largest diameter, which is that from the crown to the chin, is in general about 5 inches. The transverse diameter between the parietal protuberances is at the same time about 3½ inches. Of 60 male and 60 female infants born at the full time, whose heads were measured by Dr Clarke, the circumference passing through the occipital process and the middle of the brow was at an average 13½ inches, while the arch from ear to ear over the crown was 7¾ inches. One measured 15 inches in circumference, and one 8½ inches from ear to ear; but none were under 12 inches in the one direction, or 6½ inches in the other.

It is well established that there is a difference in the average dimensions of the male and female, even in the fetal state. Roederer found the mean length of 16 male children born at the full time to be 20½ inches, and of 8 females only 20½; and of the 60 male and 60 female infants measured by Dr Clarke, the average circumference was 14 inches in the former, and only 13½ in the latter; and the parietal arch was 7¾ in the former, and 7½ in the latter. Of 120 infants, in 6 only, which were males, did the circumference of the head exceed 14½ inches.

The weight of the adult male varies from 9 stone to 11 Weight or 12. Ten stones, or 140 lb., may be stated as the average. The female weighs about 8 stone, and rarely more than 10. After the age of 35 or 40, when fat begins to be deposited, the weight rises considerably; and the average weight at this age is from 13 to 14 stones. In some extraordinary examples of corpulence, combined with large stature, the weight of the body amounts to 20 and 25 stones.

The average weight of the fetus in the early months is uncertain. According to Mr Burns, it weighs about 2 oz. in the 12th week; about 1 lb. in the 6th month; and about 4 or 5 lb. troy in the 8th month. At the period of birth the mean weight is about 7 lb. avoidupois. Dr William Hunter states, that of several thousand new-born perfect infants weighed at the British Hospital in London by Dr Macaulay, the smallest was about 4 lb., the largest about 11 lb. 2 oz., and the greater number varied from 5 to 8 lb. avoidupois. He knew no instance of a new-born infant weighing 12 lb. Of 60 male and 60 female infants weighed by Dr Clarke, the lightest was 4 lb., the heaviest 10 lb., and the average 7 lb. 13 dr. avoidupois. The average weight of 26 children at the natural period, weighed by Roederer, was about 6½ lb.; the lightest about 5½ lb. and the heaviest about 8 lb.

The difference between the weight of the male and female infant at birth is estimated by Dr Clarke at about 9 oz. avoidupois, which agrees with the results obtained by Roederer.

In the case of twins, the average weight of each twin is in general less than that of children born at single births; but the combined weight of both is greater. Dr Clarke found the average weight of 12 twins to be 11 lb. avoidupois each pair; the heaviest being 13 lb., and the lightest 8½ lb. Mr Burns, however, states that he has known instances in which An important and useful point is to determine the average size and the dimensions of the principal organs of the human body in the adult state. Krause has, with this view, given the measurements of all the regions and the dimensions of most of the organs. All these modes of estimating the size of organs, however, are fallacious. The only one which can be employed with any precision is to ascertain the average weights of organs, and to note the proportion which these weights bear to that of the whole body. Attempts of this kind, applying, however, only to certain organs, have been made by different inquirers.

The organs specified were found, according to numerous trials made by Dr Clendinning, in males between the ages of 21 and 60 years, to weigh on an average, at the following rates:

| Organ | Ounces | Grains | Libras | Ounces | |-------------|--------|--------|--------|--------| | Brain | 46 | 20,226 | 2 | 14 | | Heart | 9 | 3,982 | | | | Liver | 53 | 23,408 | 3 | 5 | | Kidneys | 9 | 4,025 | | | | Spleen | 5 | 2,188 | | | | Pancreas | 2 | 1,148 | | | | Stomach | 5 | 2,188 | | | | Lungs | 46 | 20,116 | 2 | 14 |

In the same persons the whole person weighed 94½ pounds, which is between 46 and 48 pounds less than the average, 140 or 142 pounds (Quetelet), at the age of 40 years.

Among the persons weighed, however, several were 124, 125, and 126 lb.; two weighed 140 lb., one weighed 133 lb., and one at 50 years weighed 200 lb.

These results differ in a very slight degree from those obtained by Dr Reid and Dr Peacock in the Royal Infirmary, Edinburgh. In 89 males the average weight of the heart amounted to 11 oz. 1 dr.; in 53 females to 9 oz. ¾ dr. In 60 males the average weight of the liver was 52 oz. 12 dr.; in 25 females 45 oz. 3¼ dr. The right kidney weighed, on an average in the male 5 oz. 7 dr.; in the female 14 oz. 13 dr. The left kidney 5 oz. 11 dr. in the male; in the female 5 oz. 2 dr.

The average weight of the whole brain (Encephalon) in 131 males, between the ages of 25 and 55 years, was found to be 50 oz. 3½ dr.; in 74 females between the same periods to be 44 oz. 14½ dr.; giving a difference of 5 oz. 4½ dr. in favour of the male brain.

The average weight of the brain proper (Cerebrum) in 95 males between the ages of 25 and 55 years, was found to be 44 oz. 3¼ dr.; in 58 females within the same periods to be 39 oz. 3½ dr.; making a difference of 5 oz. 0¼ dr. in favour of the cerebrum of the male.

Special Anatomy has been divided, according to the classes of textures of which the human body is composed, into different parts, with appropriate denominations. Thus the anatomy of the bones has been named Osteology, Osteography, and Skeletology; while that of the soft parts in general has been denominated Sarkology. Where more minuteness is attempted, the anatomy of the soft parts has been still further subdivided into that of the ligaments, Syndesmology; the muscles, Myology; the vessels, Angiology; the nerves, Neurography and Neurology; the membranes, Hymenology; the glands, Adenography and Adenology; and the internal organs, Splanchanology.

Though these are convenient terms to designate the several divisions of Special Anatomy, they afford little assistance in the general arrangement of the subject. It is justly observed by Bichat, that this arrangement, if such it can be named, is objectionable, by separating different organs which ought to be united. It is indeed remarkable only for connecting organs by arbitrary, and often unnatural principles; and though it may answer in a subordinate manner, it is unfit to furnish the principles of a general and natural mode of arrangement.

The most eligible method is that which arranges the organs according to their physiological purposes—a method adopted by Haller and Soemmering, but which required the hand of Bichat to give it its full and perfect development, and which has since been adopted from this author by most subsequent writers.

According to this method, the organs of the human body may be arranged in three great classes: first, those pertaining to the animal functions, or which establish the connection between the individual and the objects of the external world—the organs of relation; secondly, those pertaining to the organic functions, or which tend to the continuance of the individual—the organs of nutrition; and, thirdly, the organs relating to the continuance of the species—the organs of reproduction. The first class contains the organs of locomotion, speech, and sensation; the second those of digestion, circulation and absorption, respiration, and secretion; and to the third are referred the organs of generation.

This method may not be altogether free from objections; several of which are anticipated by Bichat. It is sufficient, however, to observe that it is less objectionable than any other; and one of its advantages is, that it furnishes a clearer and more precise idea of the connection of the different classes of organs of the animal body than any other yet proposed.

This method of arrangement may be conveniently exhibited in the following table.

I. Organs pertaining to the Animal, Voluntary, or Relative Functions.

1. Locomotion. - Instruments—Bones, Cartilages, Ligaments, and Fibro-cartilages. - Agents—Muscles, Tendons, and their appendages.

2. Sensation. - The Organs of Proper Sensation—Smell, Sight, Hearing, and Taste. - The Organs of Common Sensation—Touch, Tact, &c.

3. Voice. - Laryngeal Voice—the Larynx. - Oral Voice or Speech—the Lips, Tongue, and Teeth.

4. Nervous Energy, or Innervation. - Central Organs—Brain, Cerebellum, and Spinal Chord. - Distributed Organs—the Nerves.

II. Organs pertaining to the Organic or Nutritive Functions.

1. Alimentary or Limnrophic Function. - Digestion. - Mastication—Mouth, Tongue, and Teeth. - Deglutition—Pharynx and Oesophagus. - Chymification—Stomach. - Chylification—Duodenum and Ileum. - Defecation and Excretion—Colon and Rectum. - Lacteal Absorption—Lacteals and Thoracic Duct. - Nutritive Circulation—Heart and Blood-vessels. - Aerating Circulation, or Respiration—Lungs, &c. - Secretory Circulation, or Secretion—Glands.

2. Circulation.

III. Organs pertaining to the Reproductive Function.

Generation. - Male or Impregnating Organs. - Female or Ootrophic Organs. - Product—the Fœtus. PART I.

ANATOMY OF THE ORGANS OF THE ANIMAL, VOLUNTARY, OR RELATIVE FUNCTIONS.

The organs belonging to the functions of animal life are those of locomotion, sensation, voice, and innervation. These organs are distinguished by two general characters, symmetry of form and harmony of action. By the first is meant that each organ possesses similar parts on each side of the mesial plane. By the second is meant that the action of that part which is on the right side of the mesial plane corresponds with that on the left.

CHAP. I.—THE ORGANS OF LOCOMOTION.

The organs of locomotion may be arranged in two orders, active and passive. The first are the agents of motion; or the organic substances which produce motion; the second are the bodies moved, or the instruments of motion. The muscles, strictly speaking, are the former, though to these are added certain appendages. The bones and their appendages constitute the second.

With the latter order of parts it is usual to begin the business of special anatomy, for obvious reasons. The bones are at once the most durable and regular in shape of all the organic solids; and as an intimate relation subsists between their mechanical figure and the soft parts connected with them, the knowledge of the former constitutes the best introduction to that of the latter species of organs.

SECT. I.—OSTEOLOGY, SKELETOLOGY.

The assemblage of bones composing the human body constitutes the skeleton, which, like the body, is divided into head, trunk, and extremities. The length of the skeleton is about an inch less than that of the body; that is, the skeleton of an individual 5 feet 8 inches in height is about 5 feet 7 inches long, and of one 6 feet, about 5 feet 11 inches long. The weight of the skeleton varies at different periods of life. That of a middle-sized adult ranges between 160 and 200 ounces. A male skeleton, measuring 5 feet 6 inches long, I found to weigh 168 ounces, or 104 lbs., avoirdupois.

The number of separate pieces amounts to 254, of which 56 belong to the trunk, 60 to the head, 72 to the pectoral extremities, and 66 to the pelvic. Of these several parts, the trunk is the most important, because, 1st, it is developed before the head or extremities; and, 2dly, because if we look to its place in the animal kingdom generally, it is the most essential and constant, and presents the general modulus or type according to which the osseous pieces composing the head are constructed.

The Trunk.

The trunk. The trunk of the skeleton consists of three parts, the spine or vertebral column, the chest or thorax, and the pelvis.

§. 1. The Spinal or Vertebral Column. (Spina Dorsi; Vertebrae.)

The vertebral column, situate in the posterior part of the trunk, the length of which it determines, unites the head to the pelvis, supports the former, and is supported by the latter. When completely developed, it consists of 29, and rarely of 30 pieces, named vertebrae (spondyli, σπονδύλαι), from the circumstance that each admits of a slight degree of rotatory motion. Twenty-four of these bones, which are in the healthy adult separate, are denominated true vertebrae (vertebrae verae). The 25th, named the sacrum, though in adult life forming a single bone, consists in early life of four separate pieces, which become consolidated, and are therefore named false vertebrae (vertebrae spuriae). The four last constitute what is named the coccyx. The column thus formed, though straight at birth, assumes afterwards several curvatures in the antero-posterior direction, giving it the aspect of the Italian f. It may be divided into four regions, the cervical, dorsal, lumbar, and sacral. In the first it is almost straight, but begins to bend backward in the second, so as to form a considerable curvature with the convex surface posteriorly. A little below the middle of the dorsal portion it bends forward, and continues to do so to the lower part of the lumbar region, where it once more bends backward, and forms the sacrum into a concave hollow. At the lower end of the sacrum it again inclines forward, and the coccyx is in general considerably incurvated anteriorly. (Plate XXVI. fig. 1.)

Besides the antero-posterior curvatures, there is in general a lateral one near the lower part of the dorsal region, on the left side, to which its concavity is directed. This has been observed by anatomists, from Cheselden, who first represented it, to Soemmerring, Bichat, and Meckel.

In length the vertebral column does not vary much; and differences in stature depend more on the dimensions of the members than of it. In thickness it augments progressively from the cervical to the sacral portions, after which it once more tapers to a point. It may be compared to two cones united by their base, the superior of which is truncated.

The vertebrae, true and false, possess certain common characters. Of these the most general is the annular shape, or a ring of bone, the opening of which, in continuity with those of the whole column, constitutes a longitudinal cylindrical cavity for lodging the spinal chord and its envelopes. It is therefore denominated the hole of the spinal marrow (foramen medullae spinalis, Socm.), or simply the vertebral hole (Bichat). Anterior to this is a mass of bone, generally the largest of the vertebra, and therefore named its body (corpus vertebrae). The anterior surface is flat, sometimes slightly convex; the posterior is always concave; the upper and lower surfaces are slightly concave, and correspond with the intervertebral fibro-cartilages.

Behind the hole the vertebra is moulded into an arch or annular segment, the outer surface of which forms seven processes. The first at the back of the vertebra on the median line is the spinous process, which may be said to be formed by the union of the spinal plates in the middle. On each side are two, which, from their situation with respect to the column, are named transverse processes. Other four, two on the upper and two on the lower surface of each vertebra, near the base of each transverse process, are named oblique, from their direction, and articular (processus articulares), because the inferior ones of the superior vertebra are articulated with the superior ones of the lower vertebra. These processes are easily distinguished by being covered with cartilage and synovial membrane. They constitute true capsular joints.

Each vertebra presents four notches or depressions, two at the upper and two at the lower surface, between the body and the oblique processes. Each of these, with corresponding notches on the vertebra above and below, forms a hole (foramen conjunctionis, vel intervertebrale), for the exit of the spinal nerves and the entrance of blood-vessels. All the vertebrae, excepting the atlas and vertebra dentata, are united in the same manner, and at the same points. The bodies are united by the intervertebral fibro-cartilages, which consist of white concentric annular layers of fibrous matter, placed in juxtaposition, and containing internally semifluid jelly. In adults this substance becomes firm and consolidated; but in the young subject it is so soft and compressible, that young persons are found to be one or two inches taller in the morning, or after they have been some time in the recumbent position, than in the evening, or after the spinal column has sustained for some hours the weight of the person. In advanced life these fibro-cartilages become still more solid and shrivelled; and in some instances they are converted into bone, so as to unite two or more vertebrae in a single mass. This change is one reason of the greater stiffness and incurvation of the spine in the old and decrepid, than in those in early life.

Besides the connection by the intervertebral cartilages, the vertebrae are united at their particular processes by means of capsular ligaments, so as to allow slight flexion and extension on each other; and at the basis of the spinous processes, by means of short, firm, and inelastic yellow chords (ligamenta flavae), named yellow ligaments. These, with a thick fibrous fascia extending along the anterior surface of the bodies (ligamentum anterius, fascia longitudinalis anterior), a similar fibrous fascia behind, lining the vertebral canal, a ligament connecting mutually the apices of the spinous processes, and the incumbent muscles, retain the vertebrae firmly in their places, and prevent them from being dislodged, unless by a force adequate to break the bones and rend the ligaments.

The vertebrae vary in structure. The bodies consist chiefly of loose cancellated tissue, without solid bone. The spinal rings and the processes are much more firm and dense.

In the fetus and infant each vertebra consists of three portions, a thick, loose mass, corresponding to the body, and two lateral arches corresponding to the spinal rings, without spinous process, and scarcely meeting. In the fetus, indeed, the posterior wall of the vertebral canal may be said to be incomplete. Soon after birth, however, the spinal plates enlarging, mutually coalesce on the median line; and from this point of union, by successive accretion, the spinous processes are gradually formed. These facts may serve in some degree to explain the facility with which tumblers and rope-dancers may be habituated in infancy to the most extraordinary inflexions of the trunk.

The vertebrae, agreeing in the characters now enumerated, differ from each other according to the regions which they occupy, and the parts with which they are connected. On this principle the twenty-four true vertebrae are arranged in three classes; the cervical (v. cervicis), the dorsal (v. dorsi), and the lumbar (v. lumborum).

The cervical vertebrae are in number generally seven, rarely six or eight; the dorsal are twelve; and the lumbar are five. (Plate XXIV. and XXV. fig. 1.)

The cervical vertebrae are distinguished by their bodies being small, with flat anterior surfaces; by the articular processes being short and flat, as well as less oblique than those of the others; by their transverse processes being short, of a triangular shape, hollowed above, and perforated at the base by a hole for the transit of the vertebral artery; by the spinous processes being short, nearly horizontal, and generally bifid; and by the vertebral hole being large and of an oval shape.

The atlas. The first and second of these vertebrae are still further distinguished by peculiarities of configuration. The first, which is named atlas, consists of a large bony ring, inclosing an irregular hole, approaching to the shape of the ancient lyre. Instead of the body, which is wanting, is a mere arch of dense bone, with an obtuse tubercle before for the longus colli muscle, and behind an articular facette which applies to a corresponding one of the tooth-like process of the second vertebra. From the extremities of this arch the vertebral hoop acquires considerable thickness, for the formation of the oblique and transverse processes. The superior oblique process is seen above on each side in the form of an elliptical cartilaginous surface, slightly concave, consisting of two parts, the anterior large, the posterior small, and terminating in a point which overhangs the sinuosity of the vertebral artery. The cavity of this superior oblique process receives the condyloid process of the occipital bone, with which it is connected by a capsular ligament, lined by synovial membrane. Below is seen the articular facette of the inferior oblique process, rounder, shorter, less concave, but covered also by cartilage and synovial membrane, and articulated with the superior processes of the second vertebra. Between these two, on the lateral regions of the vertebral ring, is the transverse process, in the shape of a triangle, the base of which is formed by the bone of the oblique processes, and the sides by the production of the anterior and posterior arch. The latter, being the segment of a smaller circle, is more distinctly circular than the former, and may be described as a strong, dense, semianular piece of bone, with a tubercle on its posterior margin at the median line, to which the rectus capitis posterior minor is attached. On the inside of the atlas, at the lower margin of the superior oblique process, is a rough surface with a depressed cavity, which marks the insertion of the transverse ligament. The space anterior to this is occupied by the tooth-like process of the second vertebra; that posterior to it, which is the proper vertebral hole, by the beginning of the spinal chord.

The atlas is connected above to the occipital bone by the capsular ligament, which surrounds the margins of the superior oblique processes; below, to the vertebra dentata in the same manner; and behind its anterior arch to the tooth-like process. To its anterior tubercle are attached the longus colli and rectus capitis internus minor; to the transverse process the rectus lateralis, the superior and inferior oblique muscles, the levator anguli scapulae, the transversi, the scalenus anticus, and the transversus colli. To its posterior arch the rectus posterior is attached.

By the condyloid processes of the occipital bone moving on the superior oblique processes, the head is bent and extended, or moved backwards and forwards on the atlas. The atlas ossifies by two points.

The second vertebra, named axis and epistrophoeus, from its motions, is distinguished by a large prominent body like a tooth (processus odontoides) issuing vertically from its body, a circumstance from which it is also named vertebra dentata. This process, which is a four-sided prism, with the top obliquely acuminated, presents on its anterior surface an articular facette, corresponding to that of the atlas. The posterior surface is rough, and corresponds to the transverse ligament. From the odontoid process the body descends somewhat below the level of the vertebral hoop, and presents at its lower margin, on the median line, a tubercle, with excavations on each side. Above, on each side of the odontoid process, are the superior oblique processes, in the shape of oval facettes, covered by cartilage and synovial membrane, and articulated with the interior oblique processes of the atlas. Below, and a little behind, is the inferior articular process, more oblique in direction, and articulating with that of the third vertebra. Between the two is the transverse pro- cess, with the vertebral hole in its base; and from the same point the spinal plates converge backwards so as to form the spinous process, which is distinct and bifid in this vertebra. Between the superior oblique process is the upper notch, which is rather a rounding of the spinal plates than a distinct depression; and between the inferior oblique process and the transverse process is the lower notch, which, with the upper one of the third vertebra, forms a complete hole for the exit of the fifth pair of spinal nerves.

The vertebral hole in this vertebra is heart-shaped, the basis before and the apex behind.

By the odontoid process it is articulated with the occipital bone and the atlas; by the upper oblique process with the atlas; and by the lower oblique process with the third cervical vertebra.

To the transverse process are attached the splenius capitis, levator anguli scapulae, scalenus, transversus cervicis, longus colli, intertransversalis secundus anterior et posterior. To the spinous process are attached the rectus capitis posterior major, obliquus inferior, spinalis cervicis, interspinalis cervicis, and multifidus spinae.

The axis ossifies from four points, one for each side, one for the body, and one for the odontoid process.

The third, fourth, fifth, and sixth cervical vertebrae are very similar. The bodies gradually increase in size to the seventh, which is generally the largest. The articular processes are also more oblique in the lower ones than in those above. The spinous processes also increase in size in the lower cervical vertebrae, and in the sixth and seventh are particularly large and prominent; and in the last are not bifid, but merely tubercular. The vertebral holes in the second and third are heart-shaped, and the lower ones triangular, with the apex towards the spinous processes. The body of the seventh also presents at its lower margin a depression, which, with a corresponding one in the first dorsal, receives the head of the first rib. The seventh, in short, may be regarded as indicating the transition from the cervical to the dorsal vertebrae.

Besides the muscles already mentioned as attached to the axis, to the cervical vertebrae are attached the lumbocostalis, the serratus posterior superior, the rhomboideus minor, the cucullaris, the splenius capitis, the upper part of the large complexus, and part of the rhomboideus major.

The dorsal or thoracic vertebra (v. dorsi vel thoracis), which are twelve in number, are distinguished by articular notches on their superior and inferior margins, which, with the intervertebral cartilage and the contiguous vertebrae, form depressions for lodging the heads of the ribs, and cartilaginous facettes on their transverse processes for articulating with similar facettes on the tubercles of the ribs. The tenth dorsal vertebra has often only one facette above, and the eleventh and twelfth have only a single facette for each of the two last ribs.

The bodies of the dorsal vertebrae are more convex and somewhat rounder before than those of the cervical and lumbar. The hole, which is smaller, is also rounder, approaching to the oval shape.

The spinal plates are broad and strong, and meet behind in long prismatic spinous processes, which are directed obliquely downwards, so that they are imbricated over each other, especially in the middle of the back. The three last are less oblique. The oblique direction and imbricated arrangement of the spinous processes are connected with the peculiar flexuous bend which the column undergoes from the lower part of the cervical to the upper end of the lumbar region.

The twelfth dorsal vertebra approaches the first lumbar in the large size of its body, in the shortness of its transverse processes, in the straight direction and smaller extent of the spinous process, and in the articular processes becoming almost vertical.

To the dorsal vertebrae the following muscles are attached: the splenius capitis et colli, trachelo-mastoides, the part of the complexus called biventer cervicis, the complexus, longus colli, transversus colli, spinalis colli, semispinalis dorsi, multifidus spinae, the inner part of the lumbocostalis, the levatores costarum, the inner layer of the tendon of the internal oblique and transverse muscles of the belly, the latissimus dorsi, rhomboideus major, cucullaris, and serratus posterior superior et inferior.

The five lumbar vertebrae are distinguished by the size of their bodies and their processes, and by the direction bar verte of the spinous and articular processes. Each body is both broader and thicker, but less convex, than those of the dorsal vertebrae. The vertebral hole also is larger, and it resumes the triangular shape as in the neck. The transverse processes are broad, flat, and large, without articular facettes like the dorsal, or arterial hole like the cervical, and are rough by the attachment of the sacro-lumbalis. Of the articular processes, which are large and have a vertical direction, the upper is concave, oval, and turned towards the median plane; the lower is convex, oval, and directed towards the lateral regions. The spinous processes are large, flattened, almost square, with thick obtuse margins, and directed straight backwards. The vertebral notches are large, and form holes much larger than at any other part of the spine.

The attached muscles are the spinalis dorsi, multifidus spinae, quadratus lumborum, the inner layer of the internal oblique and transverse, and the outer layer of the latter, the external and internal parts of the lumbocostalis, the latissimus dorsi, serratus posterior inferior, the diaphragm, and the psoas.

The sacrum, composed in early life of five pieces, which are afterwards consolidated into one, may be regarded as a series of imperfect vertebrae conjoined into a single mass. It is a symmetrical bone, of a triangular shape, with the base attached to the last lumbar vertebra, the apex, which is obtuse, adhering to the os coccygis, and the sides wedged between the bones of the pelvis.

The anterior or pelvic surface is concave, with the base, sometimes named the promontory, prominent and overhanging, the apex and the lateral margins incurvated forwards, and corresponds to the rectum. It presents in general four, sometimes five pairs of oval holes, which communicate with the spinal cavity, and between each of which may be seen a transverse ridge marking the lines of junction of the several bones; and in some instances the inner is so imperfect that a deep line is left. These holes, therefore, through which the nerves pass from the spinal chord, are quite analogous to those formed by the union of the vertebral notches. The posterior surface of the sacrum is much more irregular. At the top are two articular processes, concave and cartilaginous, for receiving the convex surface of the inferior articular processes of the last lumbar vertebra. Outside of these is a deep notch, which, with that of the same vertebra, forms the posterior vertebral hole; and outside of this is a tubercle, which corresponds to the transverse processes of the true vertebrae. Below the notch on each side is a series of four holes, which, like those of the anterior surface, communicate with the cavity of the bone, and allow the posterior nerves to issue from the chord. On the median line, between, there is an irregular bony ridge, or rather a series of three spinous processes, short, obtuse, and separated by shallow depressions. The third of these diminishes gradually in the longitudinal direction till it is entirely lost. opposite the fourth pair of sacral holes, leaving between two ridges a triangular opening, which often communicates with the interior of the spinal cavity, and, when it does not, marks the lower termination of that cavity. In the former case it is closed by the posterior sacro-coccygeal ligament.

The sides of the sacrum, which are rough, and of an irregular cuneiform shape, present two surfaces,—one anterior, something cartilaginous, for articulating with the iliac bones,—the other posterior, marked by two deep sinuities, in which are lodged the sacro-iliac ligaments. The inferior termination of the sides tapers towards the apex or coccygeal end. The surface is rough for the insertion of the sacro-ischiadic ligament, and it is terminated by a notch for the exit of the fifth pair of posterior sacral nerves.

The structure of the sacrum, like that of the vertebrae, is cancellated, and most loose in the site of the spinal plates and processes. Its mode of ossification is analogous to that of the vertebrae generally. On the middle plane appear five points, which correspond to the bodies of the false vertebrae, or the individual bodies of the sacrum; and on each side of these are formed two others, which become eventually the ridges of bone between the anterior and posterior sacral holes and the spinal plates. As these enlarge, they coalesce; and consolidating, leave only on the pelvic and dorsal surfaces the rows of holes through which issue the sacral nerves. It hence results that the sacrum is ossified from fifteen separate portions of bone.

Besides the muscles connected with the lumbar vertebrae, the sacrum gives attachment to part of the gluteus maximus and the pyriformis.

The sacrum is attached above to the last lumbar vertebra by the intervertebral fibro-cartilage, the capsule of the two articular processes, and the yellow ligament of the spinous processes; to the iliac bones by the sacro-iliac synchondrosis, and to the coccyx by a similar fibro-cartilage. (Plate XXIV. fig. 1, S.)

The coccyx is a symmetrical bone, triangular, occupying the posterior and inferior parts of the pelvis, attached by its base to the sacrum, and with the apex free and slightly incurvated forwards, so as to terminate in a hooked point, which has been supposed to resemble the bill of the cuckoo, (κοκκυξ, cuculus.)

The anterior or pelvic surface is concave, marked with transverse grooves covered by periosteum, and supporting the lower extremity of the rectum. The posterior or outer surface is convex, gibbous, and unequal, for the insertion of the sacro-coccygeal ligament and some fibres of the large gluteus, and, like the anterior, is also marked by transverse grooves.

The base or upper end of the coccyx is concave before for articulation with the sacrum, and presents behind two tubercles continuous with those of the spinal region, and on the sides two notches, which, with those of the sacrum, form holes for the fifth pair of sacral nerves. The margins of the bone are rough, for the attachment of the small sciatic ligament, and meet below at an angle, which is sometimes bifid, sometimes obtuse, and to which the levator ani is attached.

The coccyx is generally cellular, with little density. The transverse grooves by which it is marked indicate its original separation into five portions, two of which becoming united, leave four and occasionally three portions, an upper, a middle, and a lower. These portions, indeed, are so long in consolidating, that they are often separate in the adult. The first is the largest; and resembles a diminutive vertebra without hole, and with truncated or undeveloped processes. A lateral portion on each side projects like a wing, the rudiments of the transverse processes; and the two tubercles above noticed, rising like horns, are imperfect articular processes, meeting those of the os sacrum. The bony ridge which descends from these are imperfect spinal plates; and as these do not meet, they leave between them a groove corresponding to the anterior half of the vertebral hole; and the spinous processes are wanting. In the second coccygeal bone, which is rounder than the first, the aliform portions corresponding to the transverse processes are also smaller than in the first; and in the third and fourth they are diminished so much that they are scarcely cognizable.

The series of bones now described form by their union what is called the backbone, chine, spine (spina dorsi), or generally, vertebral column. Viewed in connection, it may be distinguished into an anterior and a posterior region, two lateral surfaces, a base, and an apex.

The anterior region is large in the neck, narrow in the back, and broad in the loins and pelvis. A series of transverse grooves of variable depth marks the bodies of the vertebrae; and a series of transverse elevated ridges distinguishes in like manner their upper and lower margins. These grooves, which in the cervical vertebrae are confined to the front, extend in the dorsal and lumbar to the sides. This anterior region is covered by the anterior vertebral ligament. On the sides it answers in the neck to the anterior or great recti, and the longi coli muscles; in the chest to the latter, to the vena azygos on the right, and the thoracic aorta on the left; in the abdomen to the abdominal aorta and the inferior cava; and in the pelvis to the rectum.

In the posterior region are seen, on the mesial plane, the row of spinous processes, horizontal above and below, and imbricated in the middle. The intervals, which are considerable in the neck and loins, are much contracted in the back, in which extension brings the processes in contact. The apices of all are in general in the same straight line; but this may be disturbed, either from the wrong direction of a process, or an unnatural position of a vertebra.

On each side are seen the intervertebral grooves (fissura interspinata), which commence at the occipital bone, and are continued with those of the sacrum. Broad and horizontal above, smaller and more oblique in the middle, very narrow below, these grooves are formed by the series of spinal plates, between which are left spaces varying in size according to the obliquity of the plates. These spaces are occupied within by the yellow ligaments, which being inserted at their inner surface, are something broader than the spaces, and without by the transversus spine muscle.

On each side also is recognised a longitudinal hollow, extending from the atlas to the lower end of the sacrum. This hollow, which is formed by the spinous processes and the transverse processes with the spinal plates below, is superficial at the neck, narrow and deep in the back, and narrow and superficial at the loins and sacrum. In this longitudinal groove is lodged the muscle named multifidus spine. (Plate XXV. fig. 1.)

The lateral regions present first the row of transverse processes, which vary in direction in different regions, chiefly in consequence of the spinal curvatures. Thus, if a vertical plane pass down along the sides of the column, the transverse processes of the neck and loins will be anterior to it, while those of the back will be behind it. In the first region these processes are distinguished for forming, by the series of holes in the base of each, a bony canal traversed by the vertebral artery, and which is com- Special Anatomy. Special Anatomy.

pleted in the intertransverse spaces by the intertransverse muscles are attached. Between them in the neck, and anterior to them in the back and loins, is a series of holes formed by the union of the vertebral notches. Through these, which are the intervertebral holes (foramina intervertebrae), and which increase in size from the neck to the loins, where they are considerable, the anterior branches of the spinal nerves pass. Their shape is elliptical and their transit short. Anterior to these processes in the dorsal vertebrae are the depressed facettes, in which, with those of the fibro-cartilages, the heads of the ribs are lodged.

The base of this column, which is supposed to be the last lumbar vertebra, is articulated with the sacrum in such a manner as to form an anterior convexity and a cavity behind. The base, however, may with greater justice be placed in the upper half of the sacrum, which, being firmly wedged between the thick posterior margins of the iliac bones, transmits to them, and thereby to the bones of the pelvic extremities, the weight of the trunk. The mechanism of this is similar to that of the keystone of an arch, which the sacrum truly represents. The perpendicular pressure on this bone is counteracted and balanced by the lateral pressure of the iliac bones; and this lateral pressure is sustained, partly by their mutual pressure on each other before at the pubis, but chiefly by the oblique pressure of the neck of the thigh-bone, and the perpendicular pressure of the cylinder of the latter and those of the leg-bones.

The upper extremity of the column, which is formed by the atlas and axis, receives the weight of the skull and its contents, which are exactly balanced on the articular cavities of the former bone. On this also the head is bent or extended by its proper muscles. Rotation is performed by the motion of the atlas with the head on the articular cavities of the second vertebra, and round its odontoid process.

The holes of each vertebra form, by union, the vertebral canal, in which are lodged the spinal chord, the origins of its nerves, and its membranous coverings. This canal, which is continuous with the cavity of the skull by means of the occipital hole above, and is completed by the sacral canal below, is not in the centre of the spine, nor is everywhere of the same dimensions. Situate behind the vertebral bodies, and before the spinal plates, it is nearer the posterior than the anterior region of the column. Large at the neck and upper part of the back, it diminishes below, and again enlarges in the loins. Its area is triangular in the cervical region, oval in the dorsal, and triangular again in the lumbar and sacral regions. It follows the different curvatures of the spinal column. In the recent state, it is formed not by the bones only, but before by the intervertebral cartilages, and behind by the yellow ligaments and the interspinous and intertransversales muscles. Lined by periosteum, by the posterior vertebral ligament, and by a quantity of loose cellular tissue, it is further covered by a cylindrical fibrous membrane, similar to the dura mater, the outer investment of the spinal chord; and within this are contained the ligamentum dentoculatum, the spinal arachnoid, and the spinal chord itself, with its anterior and posterior nervous roots on each side, and its appropriate blood-vessels. In early life the soft parts predominate; and the canal and its component bones are then susceptible of much freer and more extensive motion than afterwards, when ossification is complete, and the fibro-cartilages acquire firmness.

In the human subject it may be viewed as a firm but flexible bony cylinder, which performs several functions at once. Resting on the sacrum, which is wedged immovably between the iliac bones, it supports the trunk in the erect position, and transfers to the sacrum, on which it rests, the weight of the head, the chest, and great part of the abdomen. In the vertebrated animals in general it incloses the spinal chord, one of the most essential and constant parts of the nervous system. In the several regions it forms a sort of posterior protecting wall to several important vital organs. Thus, in the neck it forms a posterior barrier to the oesophagus, the windpipe, and the great sympathetic. In the back it constitutes the posterior wall of the chest; and in the loins and pelvis it is the posterior wall of the abdominal viscera and the large vessels.

In answering these ends, it is important to remark, that the firmness and mechanical arrangement of the spinous processes are of essential service. Their imbricated arrangement renders it impossible for any foreign body to enter the vertebral cavity and injure the spinal chord, unless between the occipital bone and atlas, or between the atlas and axis; and even at these points much precision is requisite to enter the cavity. Between the axis and the third vertebra it is more difficult, and below this next to impossible, without breaking the spinous processes.

With this character of security and support, the vertebral column unites a high degree of flexibility. Though the degree of motion between each vertebra is trifling, yet between several it is considerable, and between the whole twenty-four it is multiplied to a great amount. The motions of which the vertebral articulations admit are those of flexion and extension, rotation, and lateral flexion. Of these, flexion is that which is most extensive; for in the anterior direction there is less impediment to the motion of the vertebrae than behind, where the spinous processes allow no great extent of motion, unless where the habit has been acquired in early life, before ossification is completed. The rotatory motion of one vertebra on another is small; but by combining the motion of several or of the whole column, it becomes so extensive that some individuals can turn the head and neck more than half round. That these motions are the passive result chiefly of the intervertebral cartilages and the articulations of the oblique processes, may be inferred from the fact, that when the former are ossified, or the latter ankylosed, the motions are much impaired generally, and wholly destroyed in the vertebrae affected.

The motions of the head on the atlas have been already shortly noticed. Those of the atlas and occipital bone on the axis are, though simple in effect, complex in mechanism. The motion, indeed, is limited to that of rotation; but this rotation is extensive. This is favoured by the horizontal position, and the large extent of the inferior articular processes of the atlas, and the superior ones of the axis, the looseness of the articular capsule, and the absence of spinous process in the atlas. The axis and its odontoid process becoming the fixed point, the atlas, and with it the occipital bone and skull, turn on the elliptical flat articular surfaces, and on the odontoid process. On the first they glide extensively, and in opposite directions, while the capsular ligaments are stretched. On the odontoid process the motion is more limited, and from right to left, and conversely; and in the latter variety of motion, the arch of the atlas before, and the transverse ligament behind, move on the anterior and posterior facettes of the odontoid process.

The anatomical construction of this articulation, however, which is so favourable to extensive motion, is attended with the disadvantage of facilitating the luxation of the atlas on the axis. Luxation, indeed, may be re- guarded as produced by too extensive motion of these bones, in which the articular processes of the former vertebra abandon those of the latter, and instead of resting on them, are placed on the same plane, while the spinous processes are separated at least half an inch. It may be further observed, that the want of fibro-cartilages between these bones before, and of yellow ligaments behind, is favourable to displacement. The effect of this change of position on the spinal chord is obvious. While the one side of the atlas is thrust off the axis, the other is forced so near its body and articular process, that it compresses the spinal chord, and may occasion palsy or immediate death, by injuring the chord above the origins of the phrenic and intercostal nerves. The vertebral arteries at the same time undergo so much stretching, that the blood cannot move through them with the natural facility.

It is nevertheless probable that displacement rarely occurs without such injury to the ligaments as to allow more extensive luxation than that now noticed. The odontoid ligaments, or the transverse, may be ruptured; and in either case the odontoid process is allowed to slip backwards, and plunges into the chord, and destroys its texture almost instantly. These ligaments may be ruptured either immediately by sudden violence, or in consequence of previous disease. In such circumstances, the injury done to the spinal chord is followed by almost immediate death, in consequence of the influence of the phrenic and intercostal nerves being suddenly suspended. In the same manner, the insertion of a cutting instrument between the occipital bone and atlas, or between the latter and the axis, so as to divide partially or completely the spinal chord above the origin of these nerves, an operation known by the name of *pathing*, is followed by immediate death.

§ 2. The Chest. (Pectus, Sternum, Thorax.)

The chest may be defined as an osteo-cartilaginous enclosure, of an irregular conoidal shape, flattened before, concave behind, and convex on the sides. Its upper extremity is truncated. Its basis is irregularly oblique. It consists of the sternum before, the twelve dorsal vertebrae behind, twelve ribs on each side, and twelve cartilages connecting the ribs and sternum.

The sternum (sternum, stipes, os pectoris) is a symmetrical, oblong, flattened bone, broad above, narrow in the middle, broad below, and terminating in a point placed perpendicularly on the anterior of the chest. It presents two surfaces, an anterior and posterior, two extremities, an upper and lower, and two margins. (Plate XXIV. fig.1.)

The anterior or cutaneous surface, covered by skin, the aponeurosis of the sterno-mastoid and large pectoral muscles, and periosteum, is marked by four transverse ridges at intervals of an inch, indicating the lines at which the separate portions of the bone were united. The posterior, internal, or mediastinal surface, is a little concave, occasionally marked by a longitudinal depression in its middle; also presents transverse lines, but rather indistinct; is covered in the middle by the mediastinal cellular tissue, above by the sterno-hyoid and sterno-thyroid muscles, and on the sides by the triangulares sterni.

The superior or clavicular extremity of the sternum presents three crescentic sinuosities; one on the middle, bounded on each side by an elevated peak, hollowed before and behind, and one on each side, incrustated with cartilage and synovial membrane. The first of these corresponds with the trachea on the inside, and has the sterno-mastoid muscle inserted on each outside. With the two lateral cartilaginous surfaces the sternal extremities of the clavicles are articulated. Between the two is the interclavicular ligament, and all round are the ligamentous fibres of the sterno-clavicular articulation. This upper extremity is about double the breadth of the bone at its middle. Below, the bone becomes narrow, and below the fourth ridge it seldom exceeds half an inch in breadth. Here it terminates in an appendage, which is generally named the pointed or ensiform cartilage (*cartilago mucronata, c. ensiformis*). The shape of this is by no means always the same. In some subjects it is a flat, thin, and pointed process, not always very firm, but more solid than cartilage; in others it is a flat thin bone, terminating in two thin hooked points. In some it is obtuse and perforated. In some it is thrust forwards, in others it is bent inwards, or towards the one side. To this process the aponeuroses of the recti abdominis are attached.

The margins of the sternum, which are generally about half an inch thick, present seven articular depressions crusted by cartilage. The first of these, in which the sternal extremity of the first rib is lodged, is immediately below the clavicular depression, superficial and rounded. The others, which are situate at the ends of the transverse ridges, and receive the cartilages of the next six ribs, are deeper, angular, and surrounded by elevated margins, to which, in the recent state, the circumference of a capsular ligament is attached. In general, the seventh depression is formed partly on the sternum, partly on the ensiform cartilage; and the intervals between the depressions are smaller below than above.

The sternum is chiefly cancellated, light, and loose, with little density, and a thin crust of compact bone. In the fetus and infant it consists of eight or nine square pieces, separated by transverse furrows, which, by the union of two, are easily reduced to seven, and afterwards to five. By the further union of two of these portions they are afterwards reduced to three; and in this state they remain so long in some subjects that Soemmering describes the sternum not as one bone, but as three. The first of these portions, which is uppermost, is irregularly heart-shaped, or rather octagonal, with the tracheal depression and the clavicular articulations above, the depression for the cartilage of the first rib on the side, and half of that for the second at its lower margin, where it unites with the second. The latter is merely the middle and longest portion of the bone, and is occasionally in three portions, separated at the costal depressions. The third or lower portion is the ensiform cartilage, the ossification of which renders the bone complete.

The ribs may be defined to be long, flat, irregular bones, with an irregular semicircular curvature, placed on each side of the chest, at intervals of an inch or less, between the dorsal vertebrae and the sternum. In general their number is twelve on each side, rarely eleven or thirteen. Of these, seven are connected with the sternum before by individual cartilages, and five are connected indirectly to the cartilage of the seventh, without attachment to the sternum. The former are denominated true or sterno-vertebral ribs (*costae verae*); the latter are styled false or vertebral (*costae spuriae, vel notae*).

Each rib varies in length, breadth, and the direction of its curvature. The upper ribs are the shortest, and most incurvated in proportion to their length. The middle ribs, or the fourth, fifth, sixth, and seventh, are the longest, and form curves of the largest circle. The false ribs, which diminish in length from the eighth to the twelfth, are the least incurvated, or form curves of the largest circle. It is chiefly from the middle set that the common characters of these bones should be derived.

Proceeding on this principle, we find that each rib may be defined as a broad, flat, longitudinal bone, not only in... Special Anatomy.

The ribs.

curved, but twisted from the direction of its original curvature. Each rib has a vertebral extremity, a cartilaginous extremity, and a body. The vertebral extremity consists of a tuberculated angular head (caput), with two cartilaginous facettes united at an angular line for insertion in the intervertebral depressions with which they are articulated. In the first and twelfth, and sometimes in the eleventh, there is one facette only corresponding to the single vertebra with which these bones are connected. Immediately before the head the rib is contracted and rounded, so as to form a neck (collum), which varies from five to six or seven lines in length; and before the neck is a tubercle or process (tuberculum) divided into two portions, one internal, smooth, cartilaginous, and uneven, articulated with the transverse processes of the dorsal vertebra; the other external, rough, giving attachment to the middle costo-transverse ligament. Anterior to the tubercle the rib is straight for about one inch, and rough by the insertion of the serratus magnus and longissimus dorsi muscles. Beyond this point, which is therefore named the angle (angulus), the rib begins to be incurvated circularly, and bent downwards, so that the surfaces, which were external and internal, become obliquely superior and inferior. To prevent confusion, however, they must still be distinguished in the same manner.

The outer surface of the rib, therefore, is convex, and forms the outer bend of the circle. Behind, it is covered by the latissimus dorsi muscle. The internal, which forms the inner bend of the circle, is convex above, and forms a concave hollow below, bounded by two sharp margins: one proceeding straight from the head forwards, till it is lost about three inches from the cartilaginous extremity; the other, more acute, from the tubercle, and following the curvature of the rib to about two inches from the same point. In this groove are lodged the intercostal artery, vein, and nerve. The internal intercostals are attached to the inner lip of the margin; the external to the outer. The upper margin of the rib is obtuse behind, where the external intercostals are inserted; but becomes acute and rough before, where the internal intercostals are inserted. The anterior or sternal extremity of the rib is broad and large, and terminates in an oval hollow, in which the cartilage is inserted. In advanced life, when the union between the rib and cartilage is intimate, this hollow becomes less distinct.

Besides these common characters of the ribs, several present peculiarities deserving notice.

The first rib is short, almost semicircular, and its direction is such that its broad surfaces are superior and inferior, not external and internal, as in the others. The head of this rib possesses only one large articular facette, corresponding with the first dorsal vertebra, sometimes one large one, and a minute one corresponding with a small space of the last cervical vertebra. Its neck is short and round, and its tubercle is identified with the angle which is wanting. The superior surface of this rib is highly important. From the head and tubercle extends a rough surface, in which are inserted part of the scalenus posterior, part of the serratus magnus, and the scalenus medius. Next to this is a smooth, deep depression, over which the subclavian artery passes; then is an eminence, to which the scalenus anterior is attached; afterwards a superficial hollow, in which the subclavian vein is lodged; and, lastly, a rough surface at the sternal or anterior end, for the subclavian muscle. The lower surface of the first rib is uneven and slightly rough, but without groove at its outer margin.

The second rib resembles the first in direction, having rather an upper and lower, than an external and internal surface. The head is angular and acuminated, and the neck contracted; and the upper surface is rough by the serratus magnus; but the lower surface, from the tubercle, begins to present an angle in the shape of an oblique surface, bounded below by a rough ridge, within which is the groove for the intercostal vessels and nerves. Anterior to this flat oblique surface the rib is twisted, and undergoes a change in direction. In the third the angle is not more distinct, and it is only in the fourth that this part is well marked. This character continues to the eleventh, when it becomes indistinct, and in which the tuberosity disappears, or at least is identified with the head, which has only one facette. The groove also is so short as scarcely to be observed. Lastly, the twelfth rib, which is often unconnected with the others by cartilage, is without tuberosity, groove, or angle, and has, like the first, only one facette at the head.

The true ribs are connected to the sternum by means of broad rounded pieces of cartilage, variable in length and direction in different ribs. That of the first rib is very short, rather broad, and its direction, though oblique from above downwards, is more horizontal than that of the inferior ones. The angle at which it unites with the sternum is acute above, and obtuse below. It is often ossified in the adult. The second is nearly horizontal, and follows the direction of the rib to which it is attached. The next five are more oblique from above downwards, as the lower end of the sternum inclines forwards, and the corresponding ribs bulge towards the base of the chest.

Each of these cartilages, invested by perichondrium, is attached by a rough surface to the anterior end of the rib; while the other extremity, which is rounded and covered by synovial membrane, is lodged in one of the articular depressions of the lateral margin of the sternum, and secured in this situation by a capsular ligament, strengthened by anterior and posterior fibrous bands.

The anterior or outer surface of the thoracic cartilages is slightly convex, the internal or posterior surface flat, inclining to concave, lined by pleura and covered by the triangularis sterni muscle. The upper margin is concave, the lower convex, giving attachment to the internal intercostal muscles, which in this region fill the intercartilaginous spaces.

The cartilages of the five false ribs differ from those of the true, in not being articulated directly with the sternum. The cartilage of the eighth rib, after bending forwards and upwards, is attached to the seventh by a tapering point with a minute articular surface. The ninth cartilage is attached in a similar manner to the eighth, the tenth to the ninth, the eleventh to the tenth, and the twelfth is either attached in the same manner to the eleventh, or hangs free, though attached to muscles connected with the others. Hence the twelfth, and not unfrequently the eleventh, are denominated floating ribs. The whole of them are mutually connected by ligamentous fibres inserted into their perichondrial covering. The outer surface of these cartilages is covered by the recti and external oblique, the inner surface by the diaphragm and transversus.

Connected with the ribs in the same manner in which those of the true ribs are, these cartilages differ, however, in taking a direction, first of descent, then of ascent or of curvature. The spaces which they leave between them, instead of being rhomboidal, as those of the true ribs, are irregularly triangular.

In structure the costal cartilages belong to those of the cavities. Analogous to those of the larynx, they are dense, firm, elastic, whitish substances, without distinct traces of organization, and seem to consist chiefly of modified gelatine, to which they are with difficulty reduced by Special long boiling. Their tendency to ossification is consider- able. In few persons above 45 or 50 are they quite free from bony points; and in many they are at this period converted into firm bone. The cartilage of the first rib, especially, is often firmly ossified before 35. When they undergo this change, certain points in their substance are observed to assume an orange or tawny colour, and to ex- hibit a porous arrangement, with great hardness, turning the edge of the knife.

By long maceration the costal cartilages become soft and gelatinous, and are finally resolved into oval patches, separated by circular or spiral lines, with numerous per- forations. It was perhaps on this account that Herissant described them as consisting of spiral fibres.

The chest

The bones and cartilages now described, with the twelve in general dorsal vertebrae behind, constitute the bony skeleton of the chest, bearing a remote resemblance to a cone, with truncated apex and oblique base, or, more accurately, to the frustum of a cone. To form a just idea of this assem- blage of parts, it is necessary to consider its surface ex- ternal and internal, its circumference above and below, its transverse diameter, and its longitudinal extent.

The anterior region of the external surface, consisting of the sternum in the middle, and the cartilages on each side, is flattened, contracted above, wider and more promi- nent below. The intercostal spaces are filled between the sternum and the ribs by the internal intercostals, behind this by the external and internal, and covered by the anterior part of the large pectoral muscle. Behind, the chest presents the vertebrae with their processes, the transverse processes articulated with the tubercles, the angles forming a line obliquely receding from the spine, the transverse grooves, the longitudinal groove on each side filled by the multifidus spinar, and the space be- tween the processes and the angles of the ribs occupied by the spinalis dorsi, the longissimus dorsi, and the sacro- lumbalis. The intercostal spaces, from the spine to the angles, are filled by the external intercostals; and anterior to this are the two layers of muscles.

The lateral regions of the chest are convex, making a larger sweep below than above. They present on each side eleven intercostal spaces, the superior of which are shorter and broader than the inferior. These spaces, which fol- low the curved direction of the ribs, cannot be accurately defined in shape. Between the angles and the cartilages, where the curvature is greatest, they are occupied by the double layer of the external and internal intercostal muscles, which, lying inclined in opposite directions, mu- tually decussate in this tract. The lateral region of the chest is covered above by the serratus magnus behind, and the two pectorals before; below by the external ob- lique on the side, and the recti before. The inferior lateral region, which is formed by the cartilages of the ribs, is therefore named the hypochondries (hypochondria).

The inner surface of the chest is, before, correspond- ent to the outer surface, unless below, where the anterior inclination of the sternum makes the antero-posterior dia- meter greater. The posterior region is marked by the row of vertebral bodies, the prominence of which forms an imperfect partition, which separates the right and left halves of the thorax; and which, notwithstanding the posterior bend which the spine undergoes between the second and eighth vertebrae, diminishes the antero-poste- rior diameter of the chest. On each side is a large con- cave hollow, narrow above, wide below, and swelling most capaciously in the middle, the walls of which, formed by the ribs and intercostal muscles, are lined by the pleura, and the cavity of which contains the lungs.

The upper circumference of the chest, or its apex, is small, oval, transversely oblique from above downwards, and from behind forwards. Bounded before by the ster- num, behind by the first dorsal vertebra, and on the side by the first rib, it is diminished by the clavicles; and while its antero-posterior diameter is occupied by the wind- pipe, oesophagus, and the large vessels connected with the heart, its lateral portions are so much contracted, that each thoracic half (demithorax) has here almost a coni- cal termination. Its dimensions in the male skeleton of average size are about 16 inches. As the first rib has little or no motion, the upper circumference remains un- changed.

The lower circumference of the chest, which is much more extensive, is said to be nearly four times larger than the upper. This, however, is exaggerated; and I find its greatest dimensions in the male to be 32 inches, exactly double the small circumference. It is suscep- tible of enlargement from the revolving motion of the ribs. The first rib remains fixed, while the lower ones are capable of being rolled outwards on their heads, tubercles and cartilages, so that the transverse diameter of the chest is enlarged. The lower circumference of the chest presents anteriorly a large triangular notch (inci- sura trigona), with the apex at the ensiform cartilage, the sides at the margins of the cartilage, and the base repre- sented by a transverse line uniting the tips of the twelfth rib on each side. This notch, which, in the recent state, is occupied by the heads of the recti muscles, with their fasciae in the middle, and the anterior margins of the ex- ternal oblique at the sides, constitutes what is called the pit of the stomach (acrobietus cordis), or the epigastric region (epigastricum).

The transverse diameter of the chest is small above, but gradually enlarges to the ninth or tenth rib. The average diameter measured between the inner margins of the first ribs on each side in the male skeleton is four and a half inches; the average diameter measured between the tips of the eleventh rib on each side is nine inches, which is also nearly the diameter between the inner mar- gins of the fifth ribs; and the average diameter measur- ed across the upper margin of the ninth rib, which is about the widest part, amounts to eleven inches. These diameters, it has been already said, are susceptible of slight enlargement, by reason of the lateral revolution of the ribs; and this motion is most extensive between the sixth and tenth ribs. Above the sixth and below the tenth it is trifling.

The longitudinal extent or altitude of the chest varies; but in the same male skeleton it amounts to twelve inches measured between the lower margin of the first rib and the upper margin of the eleventh, which may be regarded as the inferior limit of the osseous part of the chest. From the top of the sternum to the plane of the ensiform cartilage the distance is five inches and a half. If from the lower margin of a mesial plane representing the medias- tinum, another plane be drawn on each side to the margins of the false ribs, the space inclosed on each side above this oblique plane will give some idea of the capacity of the thoracic cavities.

The dimensions above stated apply chiefly to the adult male, from about thirty to thirty-five years, and of average size. In the female the chest is generally smaller in every direction, rounder, and more taper towards its inferior region. Above, as far as to the fourth rib, it is said to be larger and more uneven before, so that it has less of the conoidal shape than the male chest. It is also shorter.

The pectoral cavity is in general symmetrical, that is, Special of similar shape and dimensions on each side of the mesial plane. Sometimes, however, without the intervention of disease, the greater convexity of two or three ribs on one side gives it a more ample appearance than on the other.

§ 3. The Peleis.

This is the name given to the irregular-shaped bony cincture which terminates the lower extremity of the trunk, and which is connected to the spinal column by means of the sacrum. It consists in the adult of four bones, two lateral portions (ossa coxae), and two on the mesial plane, the sacrum and os coccygis. The latter two have been already described. The lateral and anterior divisions now come under examination.

These consist of two bones, one on each side, united with each other before by means of fibro-cartilage, and receiving between them behind, the sacrum, to which they are in like manner united by fibro-cartilage. These bones, which are denominated ossa innominata, coxal or haunch-bones (ossa coxae), are of a very irregular shape, and may be divided into three regions, the superior or iliac, the anterior or pubal, and the inferior or ischial. These regions it is not easy to define accurately; but they will appear in the course of description, and they correspond to the original divisions of the bone in the fetal state.

The coxal bone presents two surfaces, an external or femoral, and an internal or pelvic; and a circumference, divided into superior margin, anterior margin, inferior margin, and posterior margin.

The external or femoral surface (dorsum), which is alternately concave and convex, presents behind a rough surface, to which the gluteus maximus is attached; between this and a semicircular rough line a lunated hollow, in which the origin of the gluteus medius is lodged; and between the upper semicircular line and the lower a convex and concave area, for the attachment of the gluteus minimus, and one or two inequalities, to which one of the tendons of the rectus femoris is attached. About an inch below is a large hemi-spherical cavity, with elevated circular margins, interrupted at the anterior and inferior corner, named the acetabulum, or cotyloid cavity, for receiving the head of the thigh-bone. Its inner surface is covered by cartilage, unless at the centre, where is a depression for the attachment of the triangular ligament of the thigh-bone. The lower part of the margin is marked by a deep notch, over which, in the recent state, is stretched a ligament, thus forming a hole for the transit of the vessels and nerves of the articular cavity. The surface behind the acetabulum is slightly convex, indicating its union with the upper edge of a part of the coxal bone, distinguished by the name of hip-bone (os ischii), and may be denominated the post-acetabular or ilio-ischial eminence; below, it is concave and sinuous, for the tendon of the obturator externus, and terminating in a sharp spine (spina ischii), to which the small sacro-sciatic ligament is attached. Anterior to the acetabulum is a large opening, named the thyroid or obturator hole, oval in the male, and triangular in the female, closed by a ligament attached to its circumference, unless at the upper part, where there is an oblique groove for the obturator vessels and nerve. The outer surface of the thyroid ligament supports the obturator externus muscle, the inner surface the obturator internus. The upper margin of the thyroid hole is overlaid by a convex ridge of bone, which is named the pubal or the horizontal branch of the pubal bone (os pubis, pecten, os pectinis) from supporting the parts of generation, and which terminates at its inner or mesial margin in a spine or tubercle, to which the outer portion of the tendon of the external oblique muscle is attached. The inner or anterior margin of the thyroid hole is bounded by a broad flat bone, irregularly rough on the surface, broad above, where it is connected with the os pubis, narrow at the middle and lower part, where it joins the ischial bone. To the upper part of this, which is named the descending branch (ramus) of the pubis are fixed the gracilis, the head of the adductores longus et brevis, part of the adductor magnus, and part of the obturator externus. The lower part, which is named the ascending branch (ramus) of the ischium, gives origin to the adductor magnus.

The inner or pelvic surface (venter) of the coxal bone may be divided into three parts. The first is posterior, rough, and irregular, for articulation by fibro-cartilage with the lateral margin of the sacrum. The second, which is abdominal, concave, and is named the iliac pit (fossa iliaica), contains the belly of the iliacus internus, bounded above by the circumference or crest of the bone; behind by a rough line which separates it from the sacral surface; before by a concave irregular bend formed above by the iliac, below by the pubal bone; and below by a sharp line (linea ilio-pectinea), which is insensibly lost on the spine of the pubis, and to the inner end of which is attached a reflected portion of Poupart's ligament, named the ligament of Gimbernat. The third or pelvic surface, which is below, presents behind a flat, irregular-shaped, concave space, occupied by the levator ani and part of the obturator internus, the inner opening of the thyroid hole, the inner surface of the rami of the pubal and ischial bones, with inequalities for the origin of the obturator internus, and a sinuosity below the ischial spine for the nation of its tendon.

The circumference of the coxal bone is very irregular. The upper or iliac portion, which is semicircular, and is named the crest (crista ilium ossis), is rough for muscular and tendinous attachments, varying in breadth from half an inch to a whole one, and is distinguished into an external and internal lip, and an intermediate space. To the former are attached the external oblique, the latissimus dorsi, and the tensor vaginae femoris; to the latter are attached the transversus and the quadratus lumborum; and in the middle space between the two is the internal oblique. The posterior end of the crest terminates in the posterior superior spinous process, to which part of the gluteus maximus and the ilio-lumbar ligament are attached, and below the posterior inferior spinous process forming the upper extremity of the ischiatric notch. The crest terminates before in the anterior superior spinous process, to which are attached the fascia lata, the sartorius, and the upper end of the tendon of the external oblique, or ligament of Poupart, or what is named the crural arch. The anterior portion presents, first a small sinuosity, which separates the superior from the inferior spinous process, to which is attached the upper tendon of the rectus cruris. Between this and an eminence in the upper or horizontal portion of the os pubis, marking its junction with the iliac bone, and which may be denominated the ilio-pubal, is a large sinuosity, in which are lodged the tapering ends of the iliacus internus and psoas major. To the ilio-pubal eminence the psoas peroneus is attached; and within the pubal eminence, and anterior to the linea ilio-pectinea, is a triangular space, to which the origin of the pectineus is fixed. This part of the circumference is terminated by the spine of the pubal bone, to which the first insertion of Poupart's ligament, or the outer pillar of the inguinal ring, is fixed. On the mesial side of this is a rough tubercular surface, which by means of fibro-cartilage is united with a similar surface on the opposite side. To this, which is named the symphysis pubis, the second insertion of the ligament of Poupart, the pyramides and the recti, are fixed. The posterior-inferior margin is most irregular. Commencing with the posterior spinous processes, which are parted by a small notch, the margin is, immediately anterior to the lower process, formed into a large hollow, named the ischiadic notch (incisura ischii), bounded before by the spine of the ischium, to which is attached the anterior sacro-ischiadic ligament, with the superior head of the gemellus without, and the coccygeus within. A pretty large hollow, in which play the belly and tendon of the obturator externus, separates the spine from the tuberosity of the ischium, a large broad rough surface, the external surface of which gives support to the quadratus and adductor magnus, the inner surface to the lower head of the gemellus and the external or inferior sacro-ischiadic ligament, while in the middle are fixed the long head of the biceps flexor, the semitendinosus, and the semimembranosus.

From the tuberosity the margin of the bone along the ascending branch of the ischium, and the descending branch of the pubis, becomes narrow till it reaches the symphysis, when it again becomes broad and more irregular. To the former margin are attached the gracilis, the transversus perinei, the erector, and the corpus cervicornum. The latter uniting with the opposite bone by means of the interpubal fibro-cartilage, constitutes the symphysis pubis.

The iliac or coxal bones consist of cancellated matter, covered by a thin layer of compact bone. In early life, and in delicate subjects, this cellular matter is loose, abundant, and rather thick. At a more advanced period, when ossification is completed, and in strong muscular subjects, the proportion of this cancellated matter diminishes and sometimes disappears, so that the bone consists of two layers of dense, compact bone; and in some, even this, in the iliac fossa, is destroyed entirely, so that the bone appears perforated.

The coxal bone is formed originally of three pieces, one for the large upper portion (os ilium), a second for the anterior or pubal (os pubis), and a third for the inferior or ischial (os ischium). In the fetus, infant, and young subject, these three bones are seen quite distinctly separate, but adhering, by means of fibrous or fibro-cartilaginous tissue, along a line drawn by the ilio-pubal eminence through the acetabulum, and over its posterior convexity into the ischial notch. At the same time the crest and margins of the ilium are covered by a cartilaginous epiphysis; the pubal bones are mutually attached by the same substance; the branches (rami) of the pubal and ischial bones are soft and membranous; the thyroid hole is merely a ligamentous notch; and the acetabulum is a broad, irregular, superficial depression, with fibro-cartilaginous margin. The connections of these three bones continue soft and cartilaginous for several years after birth, generally to the tenth, twelfth, or fourteenth, sometimes later; and this is the reason why the os innominatum has been described as consisting of three bones, the os ilium, os pubis, and ischium. After the last-mentioned period, however, these bones are firmly consolidated into one piece, in which, nevertheless, the original marks of separation may be recognised in the ilio-pubal and post-acetabular eminences above, and the meeting of the pubal and ischial rami below. The coxal bone, therefore, which thus becomes a single solid piece in the adult, ought to be always described as such; and the distinction into three component parts, which is confined to the foetal and early period of life, belongs to the history of its ossification.

The coxal bone is united to its fellow of the opposite side by the symphysis pubis, and behind to the sacrum by the sacro-iliac fibro-cartilage (synchondrosis). Both of these junctions are occasionally ossified in advanced life. By the cotyloid cavity it is articulated with the head of the thigh-bone.

The coxal bones on each side, with the sacrum wedged between them behind, and the os coccygis attached to its extremity, constitute an irregular-shaped osseous cincture, something conical, with the base above, and the truncated apex below. This shape, with the manner in which it supports the abdominal viscera and several of the urinary and genital organs, has given it the name of basin (le bassin, das Becken, pelvis). In this it is requisite to consider the external and internal surface, the upper and lower circumference, the transverse diameters, the direction, the outlets and their dimensions.

The external surface comprehends four regions, the anterior or pubal, the posterior or sacral, and two lateral.

The anterior region presents the pubal articulation (symphysis) on the median line, and on each side the pubo-ischial rami, the thyroid hole and its margins, and the acetabulum or articular cavity. The posterior region presents on the median line the sacral spinous processes or spinous ridge, the triangular depression which terminates the spinal canal, the suture uniting the sacrum to the coccyx and the posterior convex surface of the latter; and on each side are the sacral grooves and posterior holes; the processes by which they are bounded without; a deep depression corresponding to the sacro-iliac synchondrosis, and which is filled by a thick bundle of ligamentous fibres; and lastly, the posterior tuberosity of the ilium, which projects much behind. The lateral regions are formed by the dorsa or external fossae of the iliac bones, bounded below by the ischiatric notches.

The internal surface of the pelvis consists of two portions,—the one above, wide, capacious, and tapering downwards, forming the large pelvis; the other narrower, with walls nearly cylindrical, and forming a canal named the small pelvis.

The large pelvis presents, behind, the sacro-vertebral articulation and the sacral promontory, and on the sides the internal iliac fossae. Before, where osseous parietes are wanting, the space is occupied by the abdominal muscles. This constitutes the abdominal division of the pelvis, and supports in the erect position part of the ileum and colon. Its transverse diameter, measured between the crests of each iliac bone, amounts to nine inches in the male, and eleven in the female.

The large or abdominal division of the pelvis is bounded below by the ilio-pubal line on the sides and front, and behind by a line drawn between the posterior extremities of each side, but following the surface of the sacrum. The outline of this, which is elliptical, with the transverse diameter longest, and its plane inclined obliquely forwards, is named the superior outlet or aperture (amittus superior) of the pelvis, and it constitutes at once the lower termination of the great and the upper boundary of the small pelvis. Its importance in the practice of midwifery renders it necessary to distinguish its calibre, which is larger in the female than in the male, into four diameters. The first, antero-posterior, from the pubal symphysis to the sacral promontory, is from four to five inches in the male, and four inches nine lines in the female. The second, transverse, measured between the iliac bones, is four inches six lines, sometimes five inches, in the male, and five inches six lines in the female. Two others, drawn obliquely from the sacro-iliac synchondrosis to the ileo-pubal eminence, are about four and a half inches in the male, and five inches in the female.

The small or proper pelvis, which is below this aperture, forms a sort of cylindrical osseous canal, more capacious, Special however, at its middle than at the extremities, the lower outlet of which is diminished by the anterior incursion of the sacrum and coccyx, while the sides are bounded by generally, the pubic branches. Before are the inner surfaces of and its di- menions, the pubic symphysis and branches, corresponding to the urinary bladder; behind, the pelvic surface of the sacrum, corresponding to the rectum; laterally, the thyroid holes, the inner surface of the ischial-bone and ilio-ischial junc- tion, and the ischial notch, completed by the anterior and posterior sacro-ischiatic ligaments.

The upper circumference is very irregular, with its plane slightly inclined forwards; larger in the female than in the male. It presents, behind, the sacro-vertebral ar- ticulation, bounded by a depression indicating the upper edge of the sacro-iliac synchondrosis; laterally, the two iliac crests terminating before in the anterior superior spinous processes; before, the hollow of the iliacus inter- nus and psoas magnus, the ilio-pubic eminence, the hori- zontal branch of the pubic bone, its spine, and lastly its symphysis.

The lower circumference, which corresponds with the inferior aperture or ano-perineal outlet of the pelvis (am- bitus inferior), is directed downwards and backwards. Bounded behind by the coccygeal bone, and on the sides by the ischial tuberosities, this outlet is thus distinguished for three eminences, separated by an equal number of notches. The situation of these eminences indicates the limits of the lower pelvic aperture. The size and dispo- sition of the notches is inversely to that of the eminences; and their arrangement is such that an eminence is oppo- site to a notch, and conversely. Thus the anterior notch, which is formed by the pubic arch, is opposite to the sacro-coccygeal eminence behind; and though the ischial tuberosities appear opposite to each other in one sense, strictly speaking their plane is each accurately opposed to the opposite sacro-ischial notch. The anterior notch is terminated above by an acute angle in the male, in con- sequence of the proximity of the pubo-ischial branches which form its sides, but by a rounded arch in the female, by reason of the separation of these branches on each side. In this notch are situate the generative organs of both sexes. The lateral notches, which are bounded be- hind by the sacrum and coccyx, before by the spine and tuberosity of the ischium, are irregular in shape, and are each subdivided into three portions by the sacro-sciatic ligaments, which secure the articulation of the sacrum and coxal bones. The first of these ligaments, the poste- rior or external, arising from the posterior extremity of the iliac crest, from the sides and transverse processes of the sacrum and coccyx by a broad, firm web of fibres, becoming small and thick at the middle, again expands, and is inserted into the ischial tuberosity. This ligament corresponds behind to the gluteus maximus, which is partly attached to it, before and medially to the small or ante- rior ligament to which it is united. The small or ante- rior sacro-sciatic ligament rises, in common with the large one, from the transverse processes of the sacrum and coc- cyx, and adhering to it for half an inch, passes more horizontally outwards to the ischial spine, in which it is im- planted by a broad, thick, fibrous web. Behind, it corre- sponds at its sacral end, and for an inch from this to the posterior ligament, and laterally to the pudic vessels and nerve; before, it serves with the posterior to complete the lower circumference of the pelvis.

By these two ligaments the ischial notch is in this manner converted into two apertures and a notch. The first of these is superior, and is bounded above by the ilio-ischial arch, and below by the small ligament and part of the posterior or large ligament. Through this hole pass the pyriformis, the sciatic nerve and artery, the gluteal ar-tery, and the internal pudic artery. The second is an ir- regular triangular hole, smaller than the upper one, bound- ed above by the anterior ligament, below by the posterior one, and laterally by the sinuous hollow between the is- chial spine and tuberosity. Through this aperture the tendon of the obturator internus passes out of the pelvis; and the external pudic artery and nerve, after bending round the upper ligament, re-enter the pelvis. The third space is a superficial notch, bounded on the outer or lateral side by the posterior ligament, and on the mesial side by the sacro-coccygeal bone. It is chiefly occupied by cellular tissue.

The dimensions of this inferior aperture are nearly the following. The antero-posterior diameter, from the coc- cygeal apex to the lower margin of the pubic symph- sis, is 3 inches in the male, and 4 inches 6 lines in the female. The transverse diameter between the ischial tu- berosities of each side is 3 inches 2 lines in the male, and 4 inches in the female. The oblique diameter, measured from the middle of one of the great sacro-sciatic ligaments to the opposite ischial tuberosity, is about 4 inches in the male, and from 4½ to 5 in the female. Of these diameters the antero-posterior is most liable to vary, by reason of the mobility of the os coccygis; but independent of this, it is always larger in the female than in the male, in conse- quence of the sacrum being less incurvated, and de- scending more in a straight line. It further appears, that in females who have borne children the incurvation of the sacrum is much less than in those who have not.

The direction of the pelvis is not horizontal, nor does it correspond with that of the trunk. Articulated behind with the lumbar portion of the spinal column, the axis of which is inclined considerably forward from the vertical plane, the pelvis partakes of the same inclination. A horizontal line drawn from the pubis towards the sacrum passes in general an inch below the tip of the coccyx; and with this a line drawn from the pelvis to the upper margin of the sacrum, representing the plane of the pelvis, makes an angle of between 80° and 85°. The sacrum inclines from the vertical plane about 35°; but the inclination of the superior and inferior pelvic apertures varies. An imaginary line drawn from the tip of the coccyx to the centre of the small pelvis, to represent the axis, cuts the line of inclination at an angle of 75°. The most accurate axis of the pelvis is a line drawn at right angles to the plane of the pelvis as above found.

The dimensions given above are sufficient to show that the female pelvis is much more capacious and ample la- terally than the male. In the female, indeed, it is im- portant to remark that the upper region of the coxal bones is more prominent laterally, and hence renders the haunches prominent and rounded, and the outline of the abdominal aperture more extensive; the sacro-vertebral angle is less prominent, and the sacrum is broader and less incurvated; the arch of the pubis is wider and less angular; the ischial tuberosities are more apart, and the cotyloid cavities even are at more distance from each other—a circumstance which determines the peculiar gait of the female. The male pelvis, on the contrary, is deeper than the female.

In the infant the pelvis is small compared with the size of other bones, and of the parts which it is to contain. The dimensions of this part, in early life, are indeed so limited, that not even the urinary bladder can be said to be contained within it. As puberty approaches, the dis- tinctive characters of the male and female pelvis begin to appear. While in both sexes the bones become larger and the cavity more capacious, in the female the addi- The head.

The upper or atlantal extremity of the vertebral column supports the head, a complicated assemblage of bones, the general shape of which is spheroidal above and behind, and irregularly cubical before and below. It is naturally divided into two parts, which are distinguished by their mechanism, their use, and the mode of their development. The first of these, the skull or cranium (cranium, calcaria), forms a spheroidal bony case, occupying the superior and posterior region chiefly of the head. The second, which is the face, is formed above by an irregular pile of bones, articulated immovably to the anterior inferior part of the skull, and below by a single symmetrical bone, articulated movably to the middle of the lower part of the skull.

§ 4. The Skull. (Cranium, Calcaria.)

The skull consists of eight bones, four of which are symmetrical and arranged on the mesial plane, and four arranged in pairs on each side. The four symmetrical bones are the frontal, the ethmoid, the sphenoid, and the occipital; the four lateral are the two parietal and two temporal bones.

The frontal bone (os frontis, os coronae, synopit) is a symmetrical bone occupying the anterior part of the skull, and forming the anterior part of the scalp and the part of the face distinguished as the brow (frontis). It may be divided into three surfaces, the external or frontal, the inferior or orbito-ethmoidal, and the internal or the cerebral, and a circumference. The external surface is frontal and temporal.

The frontal surface, which is convex and regularly arched, presents on the median line a ridge, indicating the original separation of the bone in two halves, the nasal protuberance, more convex in age than in youth, and corresponding to the smooth interval between the eyebrows (glabella), a serrated margin articulated in the middle with the nasal bones, on the sides with the ascending processes of the superior maxillary bones, and, lastly, the nasal spine, which supports the nasal bones. (Plate XXV. fig. 2. n.)

On each side of the median line are the large smooth surface of the upper part of the frontal bone, the frontal protuberances (tubera frontis), large in youth, small in advanced age; the superciliary arch (supercilium), an irregular convexity extending transversely about an inch on each side of the mesial line, most prominent within, where the corrugator supercilii is fixed; and, lastly, the orbital arch, large and prominent at its temporal angle, smaller and more rounded at its nasal, and presenting either a hole, or a notch covered by a ligament (c. c.), and through which pass the frontal artery and nerve. The nasal end of the orbital arch, sometimes named the internal angular process, is insensibly lost in the serrated surface, where it joins the superior maxillary bone.

The temporal process, which is prominent, terminates in a serrated surface, which is articulated with the malar bone. Exterior to the frontal protuberance is a curvilinear ridge (d.), which gives attachment to the fascia of the temporal muscle, denotes the posterior boundary of the space in which that muscle is lodged, and separates the proper frontal from the temporal surface of the frontal bone. This ridge, descending in a circular direction, terminates in the temporal process at the opposite side to that of the orbital arch (n. a.) The triangular segment cut off by it is convex above and concave below.

The orbito-ethmoid surface is irregular. It presents first on the median line a quadrilateral notch with serrated margins, in which the ethmoid bone is articulated. These margins consist in adult subjects of two plates, between which are seen segments of the frontal and ethmoidal sinuses. In the outer of these tables are generally one or two holes, or notches, which, with the ethmoid bone, form holes (foramen orbitarium internum anterius et posterius). Through the former pass the ethmoidal twig of the nasal branch of the ophthalmic nerve; through the latter the posterior ethmoidal artery and vein. On each side of the ethmoidal groove is a triangular concave surface, which forms the vault of the orbit, near the outer margin of which, and within the external angular process, is a superficial pit for the lacrimal gland, and towards the nasal side a depression for the reflected tendon of the superior oblique muscle.

The internal or cerebral surface, which is concave, covered by the dura mater, presents on the median line a groove, the beginning of the sagittal, in which the superior longitudinal sinus is lodged, and the margins of which, converging below, form a crest corresponding to the upper margin of the falx. Below this is the foraena cerebri, which in the bone communicates with the two canals belonging to the nasal bones, but in the recent state allows some veins to pass from the nose to the longitudinal sinus. It is sometimes common to the frontal and ethmoid bones. (Plate XXV. fig. 3. c.)

On each side the frontal bone presents the large cavities, in which are contained the anterior extremities of the hemispheres of the brain; and above these the bones rise in the manner of a vaulted arch. The whole inner surface is moulded into alternate pits and eminences, called digital and mammillary respectively, and which correspond to the eminences and depressions of the cerebral convolutions. These are most conspicuous at the lower part, where the surface is traversed by minute vascular grooves.

The circumference of the bone is serrated all round, for articulation with the contiguous bones. The posterior margin is nearly of an elliptical outline, straight, and interrupted below by the quadrilateral notch. Above, where the frontal is articulated with the parietal bones, the serrated processes proceeding from the outer table are largest and longest. Below, where the frontal is articulated with the lower angle of the parietal and wing of the sphenoid bone, the internal table is most prominent, so that the spheno-parietal suture is imbricated. Between the temporal and orbital fossae this separation of the tables forms a triangular rough surface, which is articulated with a similar one, the triracual surface of the sphenoid bone; and between this and the quadrilateral notch the margin is articulated in the same manner with the anterior margin of the sphenoid bone. Lastly, the serrated and cellular margins of the quadrilateral notch are connected with the ethmoid bone.

Besides these cranial bones, the frontal is articulated with the following bones of the face,—the nasal bones by the middle of the nasal suture, the superior maxillary bones by its sides, the lacrymal bones by the anterior end of the ethmoidal groove, and with the malar bones by the external angular processes.

The frontal bone, which is thick at the nasal protuberance and the external processes, and thin at the orbital regions, is ossified by two points, which, appearing at the frontal protuberances, proceed by radiation as from a centre towards the circumference of the bone. In the fetus and early infancy the bone thus consists of two lateral portions placed between the pericranium and dura mater, with a longitudinal interval on the mesial plane, a transverse one on the site of the coronal suture, and a triangular chasm at the angle between the two. This chasm, with a similar one between the frontal bones, forms a quadrilateral lozenge-shaped space, at which the motion of the brain is distinctly felt both at birth and for months after, and which is therefore named the fontanelle, or the anterior fontanelle (ossis palatini; bregma), or the open of the head. As the ossific process advances, the lateral margins of the bone extend, and the mesial margins extending mutually, at length coalesce, first at the nasal protuberance and along the forehead, afterwards above, until the fontanelle is progressively diminished and at length obliterated. This junction is effected by the formation of serrated processes, which are mutually dove-tailed into each other; and for some years after birth the frontal bone consists of two similar halves articulated by a middle suture. In some few instances, especially in the female, this continues for many years; and the individual is found after death to have the frontal bone in two halves, with a middle suture. More frequently, however, the suture is obliterated by the consolidation of its serrated margins, and the frontal bone consists of one piece. The points of ossification remain long distinct in the form of the frontal protuberances. But eventually, from the uniform elevation of the margins of the bone, they become less conspicuous; and in old age they disappear more or less completely, leaving a surface uniformly uneven.

The ethmoid or sieve-like bone (os cribiforme), which is symmetrical and occupies the quadrilateral notch of the frontal bone, consists of several bony plates arranged at right angles, and parallel with each other, so as to give the whole a cubical shape. It consists of four parts, a horizontal plate, occupying both sides of the mesial plane; a vertical plate at right angles to it, and corresponding with the mesial plane; and a lateral plate on each side, also vertical and parallel to the middle plate. In the bone thus formed the following circumstances deserve attention. (Fig. 5.)

The superior surface, cerebral, covered by dura mater, is formed by the horizontal plate, perforated by numerous holes (lamina cribrosa), through which pass the fibrils of the olfactory or first pair of nerves depressed longitudinally on each side, but surmounted in the middle towards its anterior half by a strong process of a triangular shape, named the cock's comb (crista galli), and to which is attached the anterior inferior extremity of the falx, or dichotomous membrane. The anterior margin of this process is generally marked by a groove which, with that of the frontal bone, forms a passage for the nasal vein into the longitudinal sinus. The posterior margin of the perforated plate is marked by an angular notch between two horns, for articulation with a salient angle of the sphenoid bone. The crista galli may be regarded as the upper division of the vertical plate, which occupies the mesial plane, and which is thick and sometimes bifid before, but thin and rough behind, where it acts as a partition to the lateral halves of the ethmoidal cavities. The sides of this middle vertical plate are furrowed by minute canals (canaliculi), traced from the foramina above, in which the nervous fibres are lodged. This plate, and indeed the lower surface of the perforated plate, are covered by a fibro-mucous membrane, which has been named the pituitary or the Schneiderian. The vertical ethmoid plate is articulated at its lower margin with the cowering and the triangular cartilage of the nose, before with the nasal spine of the frontal bone, and behind with the median crest (processus azygos) of the sphenoid bone.

The lateral portions of the ethmoid bone consist externally of a smooth flat bone (os planum of the ancients), Special Anatomy, which forms the inner or nasal wall of the orbit, internally of two bones convoluted on themselves, and which are distinguished as the superior and middle turbinated bones (concha, osse turbinate superius et media, ossa spongiosa). These bones are seen most distinctly behind; but to form a correct notion of their figure, it is requisite to detach the lateral portions and examine them separately, when the following peculiarities may be recognised. The ossa plana on each side terminate in concave oblong quadrilateral plates, diverging outwards from the vertical plane. At the internal edge of these quadrilateral plates is seen above a convex bone, with numerous minute perforations, the orifices of short canals. This is the superior turbinated or spongy bone. Below, and a little to the external side, is a small groove, separated by a thin plate from a larger cavity, which is the superior meatus, leading into the posterior ethmoid cells. Below this, again, is the osseous plate, with perforated edges turned on itself from within outwards, so that its convex side is towards its fellow, and its concavity is below and laterally, and separated by another thin plate from the lower margin of the ossa plana. This is the middle turbinated bone, the longitudinal cavity of which communicates with the lower or nasal surface of the bone, and is bounded on its outer margin by the lower margins of the ossa plana, where they are articulated with the inner margin of the orbital plate of the maxillary bone. The anterior deficiency of the ossa plana is occupied by the lacrymal bones.

The internal surface of these bones generally is covered by a thin fibro-mucous membrane, partaking of the characters of periosteum at its attached, and of mucous membrane at its free surface.

The ethmoid is articulated with the frontal bone, the sphenoid, the superior maxillary bones, the nasal, the lacrymal, the palate bones, the inferior turbinated bones, and the vomer, at the parts already indicated.

In structure the component plates are compact, unless at the crista galli, which contains some cancellated tissue, and the middle and superior turbinated bones, which seem less dense than the horizontal plate.

The ethmoid bone consists in the foetus of loose, soft, brown-coloured substance, contained in a thick vascular membrane, and disposed in the cubical shape, but without the complicated arrangement of convoluted plates by which it is afterwards distinguished. Into this the nervous fibrils penetrate, and are observed to be ramified. This continues at least four or five months after birth, when these fibrils become surrounded with compact bone deposited in their interstices, and in this manner the perforated plate is formed by deposition round the nerves. About the same time, on the mesial plane is observed a vertical plate, which gradually becomes condensed into solid bone, in the shape of the crista galli and middle partition. Soon after, as the bone increases in size, excavations are formed, and the soft uniform substance is removed, while plates of thin but solid bone interposed between thick vascular membranes are observed to be formed. The plates, which are slightly convoluted, become thinner and more solid, and are at length moulded into the superior and middle turbinated bones. The ethmoid is generally complete about eighteen months after birth; and about the second year its different component parts may be recognised. The holes of the perforated plate are, however, larger and more numerous at this age than afterwards. The minute grooves (canaliculi) described by Scarpa, in the lateral portions, are also more distinct and larger than subsequently. It ossifies therefore in four points; The sphenoid, wedge-like or cuneiform bone (as cuneiforme, os sphenoides, Sphenoideum)—a symmetrical bone, of a very irregular and complicated shape, wedged as it were between the bones of the skull, may be distinguished into cerebral or superior, and anterior-inferior or external surfaces. By the ancient anatomists it was compared to a bat with the wings expanded, and is by them distinguished into a body and wings, great and small. (Fig. 4.)

The cerebral surface, covered by the dura mater, is superior, and forms part of the internal base of the skull. It may be distinguished into four parts; the middle, the upper anterior, and two lateral. The middle consists of a smooth surface, on which lie the olfactory or first pair; a transverse groove for the commissure of the optic nerves; a transverse eminence named the olivary (processus olivaris); a deep quadrilateral pit in which is contained the pituitary gland, named the Turkish saddle (sella Turcica, epiphysium fossa pituitaria), with a slight groove on each side for the transit of the sixth pair of nerves, and bounded behind by an elevated eminence, with two processes, named the posterior clinoid or couch-like processes. The sides of the sella Turcica, especially before and behind, present generally a pit, in which is lodged part of the carotid artery. The anterior serrated margin of this surface is articulated with the ethmoid bone; the posterior with the cuneiform process of the occipital bone.

The upper anterior portions consist of two triangular spaces, united to the middle by their base. This surface, which corresponds to the anterior lobes, is bounded before by a serrated margin articulated with the frontal bone, behind by a smooth curved margin, which corresponds to the Sylvian fissure, and marks the separation of the anterior and posterior cerebral lobes. This arch, which may be named the sphenoideal, terminates before in a sharp process, named the ensiform, articulated with the frontal bone, and behind in a similar though smooth process named the anterior clinoid. Anterior to this, and between it and the olivary process, is the optic hole (foramen opticum), for the transmission of the optic nerves on each side. Behind this hole, and on each side of the olivary process, is the groove in which the internal carotid is lodged. The triangular surfaces now described are commonly named the small wings (ala minores sive superiores), or the wings of Ingrassias. (Fig. 4, a, a.)

The lateral surfaces are concave, marked with cerebral depressions and vascular grooves, four-sided, low behind, but rising to an angular peak before, and are commonly named the large wings (ala majores, alae mediae, Soemm.). (A, A.) From the small wing of Ingrassias it is separated by a longitudinal fissure, extending obliquely from the sides of the sella Turcica upwards and laterally. Through this opening, which is large below and narrow above, and is variously named the superior orbital fissure, the sphenoideal fissure (foramen lacrimum superius et anterius, l, l), pass the third pair or oculo-muscular nerves, the fourth or pathetic, the first or ophthalmic branch of the fifth, and the sixth or abductor nerves, the optic vein, and a branch of the lacrymal artery. Behind, and a little to the outside of the sphenoideal fissure, is the round or superior maxillary hole (foramen rotundum, r, r), for the transmission of the second or superior maxillary branch of the fifth pair; and still more posterior and laterally the elliptical hole (foramen ovale), for the transmission of the third or inferior maxillary branch of the fifth pair. This part of the large wing terminates behind in an angular process named the spinous, articulated with the petrous portion of the temporal bone, and in which is seen the spinous hole (foramen spinosum), through which a branch of the external carotid, the middle meningeal artery (arteria durae matris media, maxima), enters the cranium to be distributed on the dura mater.

The lateral surfaces terminate before in an elevated recurved peak, surmounted by a triangular surface mostly serrated, but smooth behind, articulated with a similar surface of the frontal bone; laterally in a concave serrated margin articulated with the convex serrated margin of the temporal bone; and behind in a smooth margin, which, with a similar one of the pyramidal portion of the temporal bone, forms the anterior fissure of the base of the cranium (foramen lacrimum anterius in basi cranii).

The anterior inferior surface presents several distinct regions. On the mesial plane, at right angles to the serrated margin, is a vertical crest or spine, which terminates below in a process denominated therefore the argus or rostrum. (a.) The upper crest is articulated with the vertical plate of the ethmoid bone, the lower with the fissure of the corner. On each side the bone is convex, from the swelling of the sphenoidal sinuses, into which may be seen a small opening, which, however, is nearly closed by an osseous plate, variable in shape, named by Bertin the sphenoidal turbinate bone. The interior of the sinuses is parted into two halves by a middle plate, corresponding to the external crest. On each side of this middle portion is the outer surface of the small wings, forming part of the orbit penetrated by the optic hole, to the circumference of which are attached the levator palpebrae superioris and levator oculi above, the depressor oculi below, the adductor within, the abductor without, and the superior oblique (trochlearis) between the two last. Between the margins of the small and great wings is the outer orifice of the sphenoidal fissure; and on the other side of this is the orbital surface, hollow, bounded above by the serrated margin of the triangular area, without by that of the malar process, and below by a smooth ridge, which, with the posterior one of the superior maxillary bone, forms the spheno-maxillary fissure. Immediately between this is the external orifice of the superior maxillary hole. External to the malar serrated edge is the zygomatico-temporal surface, hollow, inclosed within three curvilinear serrated margins and two rounded ones, and parted into two portions, the temporal and zygomatic, by an elevated ridge, to which are attached aponeurotic slips of the temporal muscle. Below this transverse crest is a concave surface, lost in the external pterygoid process, and forming part of the zygomatic fossa, terminating, like the similar part of the large wing, in the spinous process, and presenting first the elliptical, and then the spinous hole.

The rest of the outer surface of the sphenoid bone terminates in two prominent bony plates, the one external, thin, and flat, the other internal, thicker, and more pointed, named the pterygoid or wing-like. These processes rise almost at right angles to the plane of the posterior part of the lateral wings by a thick prismatic piece of bone, common at first to both. Soon, however, they become distinct, especially behind. The external plate, which is thin, broad, and sharp, rises from the lateral portion between the round and oval hole, and, with its plane turned obliquely outwards, terminates in an end round below and before, sharp behind. (b, b.) To the outside of this plate, which is irregularly rough, with part of the zygomatic fossa, is attached the external pterygoid muscle. The inside of the external plate is concave, and forms, with the internal, part of the pterygoid fossa, in which are lodged the internal pterygoid muscle and the external periapophysinus. The internal pterygoid process, rising on the inside, narrower and more curved, terminates in a bent point named the unciform or hook-like process (c, c), over which in a peculiar groove moves the tendon of the external peristrophylomus. The base of the external process generally presents a longitudinal superficial depression named the navicular.

Between the external and internal is left a triangular space, which is completed by the pyramidal portion of the palate bone. The base of the internal pterygoid process is penetrated by the Vidian canal (canalis Vidianus), larger before than behind, through which is reflected the posterior twig of the sphenopalatine ganglion, sometimes named the Vidian nerve (Plate X. fig. 2), to join the sixth at its connection with the great sympathetic, with some blood-vessels.

The posterior part of the body of the sphenoid bone presents a quadrilateral surface of some extent, rough, cartilaginous, and sometimes excavated into small cells, for articulations with the cuneiform or basilar process of the occipital bone. In the young subject this surface is soft and cartilaginous; but as age advances it becomes more solid, and is at length inseparably ossified with the occipital bone. From this circumstance Soemmerring describes the sphenoid and occipital as one bone, under the name of spheno-occipital; a method in which he has been followed by Meckel. The bone, however, is so complicated in shape and the arrangement of its parts, that it is perhaps more intelligible to describe it separately.

The sphenoid bone is articulated with all the bones of the skull at the points already indicated, and with the following bones of the face—the malar, the palate bones, and the vomer, sometimes with the superior maxillary.

It consists, when fully formed, chiefly of compact bone; for the plates even of its cells, though thin, are compact and firm bone, and its general density is considerable.

In the fetus the sphenoid bone, after remaining cartilaginous till the third month, begins to ossify in the lateral portion, near the roots of the pterygoid processes. Two other points of ossification appear on the large wings, and coalescing with those already formed, constitute a single mass on each side for each lateral portion. About the same time the body in the sella Turcica begins to be formed; and shortly after the small wings are formed separately, and coalesce, first with each other, and then with the body. In the fifth month the bone has the same figure which it retains through life, but the extremities of the wings are soft and cartilaginous; the body of the bone is uniform, loose, bony matter; the holes are large and imperfect; the optic hole is triangular; the inferior maxillary hole and the spinous are incomplete behind—sometimes the latter is not formed; and the Vidian canal is a mere fissure between the base of the external and internal pterygoid processes. The bone at this time consists of five portions, one for each small wing, one for each large wing, and one for the body of the bone. At the period of birth, though these parts are still separable, in general the small wings become united with the body, and the bone thus consists of three pieces. Eventually, by the union of the two large wings with the sides of the body, the bone is consolidated into one portion, the optic foramen is rounded, the oval hole completed, and the Vidian fissure is at the same time converted into a canal. In this state the sphenoid continues for several years, growing in every direction, and diminishing the size of its several apertures; till, about the age of puberty, the body becomes excavated into two lateral cavities with compact walls, separated by middle partitions. These are the sphenoidal sinuses, the formation of which is generally simultaneous with the completion of the bone in all its parts.

The occipital bone (os occipitis, os prorsus), symmetrical, of a rhomboidal or trapezoidal shape, placed on the median line, occupying the posterior inferior region of the skull, may be distinguished into three parts, the occipital bone proper, the condyloid processes, and its cuneiform or basilar process. It presents two surfaces, an external or occipital, and an internal or cerebral.

The external surface is convex and smooth above the middle, where it is covered by pericranium and the tendinous fascia of the occipito-frontal muscle. Nearly in the middle the bone is elevated into an irregularly triangular eminence named the occipital protuberance (tuber occipitale), the size and shape of which vary according to the energy of the muscles connected with the strong fibrous fascia named the cervical ligament. When most strongly marked, the apex of the protuberance to which the trapezius, by means of the ligament now mentioned, is fixed, is prominent downwards, and occasionally incurvated or unciform. From this prominence a line may be traced, obscurely at first, distinctly below, descending to the great aperture (foramen magnum), for the transmission of the spinal chord. To this ridge or crest (crista occipitis), which is not always exactly in the middle, a fibrous fascia of great strength is attached, from the protuberance to the aperture, giving support and attachment to the muscles on each side, and named the posterior cervical ligament (ligamentum cervicis, ligamentum nuchae). On each side of this ridge the surface is marked by various irregularities, the effect of muscular impressions.

A semicircular ridge, extending from the protuberance on each side to the margins, where it joins a similar ridge on the temporal bone, and named the superior semicircular, gives attachment above to the occipital part of the epicranium, the lateral parts of the trapezius below, and at its marginal end to that of the sterno-mastoid.

When the crest begins to be distinct, a similar ridge proceeds in a semicircular direction to the margins of the bone, where it becomes more elevated, and occasionally changes its direction by a slight bend downwards and forwards. To the space between these two lines, which is rough and irregular, the complexus, and part of the rectus capitis posterior major, are attached within, and the splenius capitis without; while the rectus capitis posterior major and minor, and the obliquus capitis superior, are inserted by a strong fascia into the superior semicircular line. (Plate XXIV. fig. 6.)

The lower region of the bone presents the vertebral aperture, generally oval, with the large diameter antero-posterior, sometimes circular, occasionally rhomboidal or lozenge-shaped. At its anterior half are the condyloid processes, tipped with cartilage and synovial membrane, elliptical in shape, converging forwards, and parted by a sinuosity in the posterior part of the cuneiform process. By this opening the spinal chord with its membranes, and the spinal nerves, pass outwards, and the vertebral arteries enter the cranium. The posterior extremity of the condyloid processes is bounded by a depression, containing generally a small hole, sometimes two, for the transit of vessels not constant; externally is a rough surface, for the attachment of the rectus capitis lateralis; and above is the anterior condyloid hole, for the transmission of the twelfth cerebral or hypoglossal nerve.

The portion of bone anterior to the great aperture is the cuneiform process, the outer surface of which is depressed behind for the insertion of the recti capitis interni majores and minores; but smooth before, where it is covered by the mucous membrane of the pharynx.

The internal or cerebral surface, which is concave, is divided more or less regularly into four compartments, in the following manner. From the apex descends a groove nearly in the median line, though generally inclining a little to the right, to near the middle between the apex Special Anatomy.

The occipital bone and upper margin of the great aperture, where it makes a rectangular turn to the right, leaving in the middle an elevated eminence, on the other side of which a similar groove, though always smaller, proceeds to the opposite margin of the bone, while from the same point descends an elevated ridge, more or less acuminate, to within half an inch of the great aperture. This arrangement produces in the inner surface of the occipital bone a cruciform appearance, which is occasionally named the *spina cruciata*, while the compartments are distinguished as superior and inferior right and left occipital fossae.

The rectangular groove, which is the continuation of the sagittal, formed in the inner surface of the parietal bones, contains first the lower part of the superior longitudinal sinus, then the lateral sinus, the plates of the *dura mater* being fixed to the lateral ridges on each side. The groove on the left side contains the left lateral sinus; and to the central tubercle and ridge the *folia* of the cerebellum is attached. In the two upper compartments, which are much marked by cerebral eminences and depressions, the posterior cerebral lobes are lodged, while the cerebellar lobes are contained in the inferior compartments. (Fig. 7.)

On each side of the large aperture is seen a short segment of a broad circular furrow, which terminates on the margin of the bone in a smooth sinuous depression. The first part is the termination of the lateral groove, containing the end of the lateral sinus; the second, the sigmoid notch, forms, with a similar one on the temporal bone, the jugular hole (*foramen lacrimum posterius in basi cranium, foramen jugulare, incisura jugularis*), for the commencement of the jugular vein, the glossopharyngeal nerve, the *nervus vagus*, and the accessory nerve. Occasionally there is a proper notch for the *nervus vagus* in the anterior part, and occasionally one for the glossopharyngeal.

Anterior to the large aperture is the inner surface of the cuneiform process, concave transversely for lodging the *medulla oblongata* before it quits the cavity of the cranium (*fossa basilaris*), marked by a groove at the sides for the inferior petrous sinuses, and terminating abruptly in a broad quadrilateral surface incrusted with cartilage, for articulation with the posterior part of the sphenoid bone.

The margins of the occipital bone posterior to the inferior lateral groove are serrated for articulation by suture with the parietal and temporal bones. The upper margins form a salient angle, nearly rectangular, for articulation with the re-entrant angle formed by the two parietal bones. The sides of this angle, however, vary in direction from the presence or absence of Wormian bones (*ossa Wormiana, trigoneta*). Another salient angle, but always obtuse, is formed opposite the superior lateral grooves, for articulation with the re-entrant angle formed by the parietal and temporal bones of each side. A third angle is formed by the jugular eminence, an elevated process placed between the inferior lateral groove and the jugular notch, and which is tipped with cartilage for articulation with a corresponding surface of the pyramidal portion of the temporal bone. Anterior to the jugular notch the margin of the bone is smooth, but articulates by fibrocartilage with the posterior surface of the temporal pyramid, leaving a small space unarticulated between the anterior extremities of both bones, which form a common aperture.

The occipital bone is thick along the crucial spine, the tubercles, and at the condyloid process; but thin in the centre of the four occipital fossae, at which the external and internal tables are united with little or no *diplac*, and are not unfrequently translucent. The cuneiform process is cancellated.

In the fetus it consists of four pieces, one for the occipital bone proper, one for each condyloid portion, and one for the basilar process. The ossification of the occipital portion commences near its middle, corresponding to a point above the occipital protuberance, and extends by radiating fibres all round to the margins of the bone. At this time the occipital portion has the shape of a *cardium*; and the apex not being formed, a space is left through which the brain is felt pulsating, named the posterior fontanelle. About the same time ossification appears in two quadrilateral portions on each side of the large aperture, and in an oblong parallelogram anterior to it. Though these enlarge and approach each other, at the period of birth the apex is still incomplete, and the posterior fontanelle is open; and even at the inferior angles of the occipital portion, where it joins the condyloid portions, a space of the same kind is left on each side. After birth, as ossification advances rapidly, the apex of the occipital portion is gradually enlarged, the Wormian bones on each side are formed, and the condyloid and basilar portions uniting with the occipital, the bone is consolidated about the third or fourth year. The traces of the lines of union may sometimes be recognised so late as the seventh year.

The occipital bone is articulated immovably by its margins with the sphenoid bone, the two parietal, and the two temporal bones; movably by its condyles with the atlas.

It is also connected with the second vertebra by means of a ligament, which passes from the odontoid process to the inner margins of the condyloid processes.

The parietal bones (*ossa verticis, ossa bregmatos, ossa parietalia*), two bones united with each other on the tal bones mesial line, are quadrilateral, quadrangular, convex externally, concave internally, occupying the upper, middle, and lateral parts of the cranium. (Plate XXVI. fig. 4 and 5.)

The external convex surface, which is covered by the *epicranium* above and temporal muscle below, presents above and behind a hole for an artery and vein, variable however in position and existence; in the middle the parietal eminence, prominent in youth, indistinct in advanced age; and somewhere between its middle and lower margin a curvilinear ridge, the continuation of that on the frontal bone, and terminating near the lower angle of the parietal for the attachment of the temporal fascia, below which the bone is covered by the temporal muscle.

The internal concave surface, lined by the *dura mater*, is marked by digital eminences and depressions corresponding to those of the cerebral convolutions. The superior edge is marked by a half-groove, which, with that of the opposite bone, constitutes the sagittal for lodging the superior longitudinal sinus; within this, depressions more or less deep, corresponding to the granules of Pacchioni; towards the centre the parietal pit, corresponding to the eminence of the external surface; and ascending from the inferior anterior angle arborescent grooves, in which the large meningeal artery is lodged. (m, m.) Parts of these grooves are occasionally converted into canals by the growth of bone over their margins.

The parietal bone is bounded by four margins. By the superior, which is serrated, it unites on the mesial plane with the opposite bone, forming the *sagittal suture*; by the anterior or coronal, also serrated, it is articulated firmly with the frontal bone, forming the *coronal suture*; and the posterior, also serrated, forms with the posterior margin of the corresponding bone a re-entrant angle, in which the occipital, occasionally with Wormian bones, is articulated. The lower margin alone, which is a concave curvature, is obliquely acuminate before, acuminate and serrated in the middle for imbrication with the temporal Special bone, and serrated behind for articulation with the upper margin of the mastoid process.

These margins form by union four angles, an anterior and posterior superior, and an anterior and posterior inferior, of which the most important is the anterior inferior, by reason of its presenting the origin of the meningeal groove on its internal surface. The parietal bone, consisting of an external and internal table, with interposed diploe, is thin, especially below its middle; and the diploe is small, and in some points obliterated. It is ossified from one point, commencing at the protuberance, and radiating all round to the margins. Previous, and some time subsequent to birth, its mesial margin and anterior and superior angle are not formed; and the brain is here covered by dura mater, pericranium, and integuments only, forming, as already mentioned, the bregma, or anterior fontanelle. By the completion of the bones, however, the margins and angles meet, and the fontanelle is closed. This is generally effected in the course of the second year.

The temporal bones (ossa temporum), rather irregular in shape, are placed on each side at the lateral and inferior parts of the cranium.

Each bone presents an external or auricular surface, an internal or cerebral, and a circumference.

The external or auricular surface presents, above and before, a large convex surface, part of the temporal fossa lodging part of the temporal muscle; before, the zygomatic process, long, pointed, and terminating in a serrated extremity, where it is united with the malar bone to form the zygoma (fig. 2, z), to the upper surface of which the temporal fascia is attached, to the lower the masseter muscle; behind, a flat surface of an irregularly rounded shape, terminating before in the mastoid process (processus mastoideus, m), and behind in a serrated margin, which unites with the occipital bone. Between the mastoid process and the serrated margin behind is a rough surface for the splenius, small complexus, and sterno-mastoid; and below is a pit, in which the origin of the digestive muscle (biventer maxillae) is lodged.

The zygomatic process is connected to the temporal bone by two roots, one of which, anterior, inferior, and transverse (processus transversus), forms the anterior brim of the glenoid or articular cavity, in which the condyle of the inferior jaw is lodged; the other, superior and posterior, forms first the external and then the posterior brim of the same cavity. Behind this posterior brim is an irregular fissure termed the glenoid (fissura Glaseri), which indicates the original line of separation between the superior or squamous and the inferior or pyramidal portion of the bone, and through which pass the tendon of the anterior muscle of the malleus, some vessels, and a nervous twig named chorda tympani.

In the angle between the mastoid and zygomatic process is an elliptical opening from five to six lines in diameter, leading into a cylindrical cavity, the direction of which is obliquely forwards. This orifice, which is the external ear-hole (meatus externus, o), leads into the tympanal cavity, from which it is separated, in the recent subject, by a thin membrane only (membrana tympani). The three lower thirds of this orifice are formed by a distinct bony ring, which is rough, and perforated by holes for the insertion of the cartilages of the external ear. On the outside of the lower part of this bony ring is a strong process, varying from half an inch to 12 lines in length, nearly round, but terminating in a sharp point, and therefore, from its resemblance to the style of the ancients, named the styloid process (z). Behind its base, and between it and the mastoid process, is a small hole, the stylo-mastoid, for the exit of the facial nerve. (Plate XXVI. fig. 2.)

The inner or cerebral surface, marked by cerebral impressions and arterial furrows, is distinguished particularly by a pyramidal eminence of bone rising obliquely from it, and a deep sinuous groove, making part of the poral bone, lateral, in which is lodged part of the lateral sinus.

The pyramidal portion (pyramis, fig. 3, p), named also the petrous (pars petrosa), from its hardness in several of the lower animals, may be distinguished as a truncated pyramid, bounded by four planes, one of which, the external, has been already described. Of the other three, one superior, marked by cerebral impressions, presents a semilunar depression for the Gasserian or trigeminal ganglion, the upper orifice of the carotid canal, a slight furrow, the extremity of the opening through which a branch of the Vidian nerve passes, and an eminence which indicates the situation of the superior semicircular canal. Another posterior, separated from the last by a sharp margin, traversed anteriorly by the groove of the superior petrous sinus, presents, first, an eminence indicating the posterior semicircular canal; and, secondly, an orifice, the internal auditory hole (meatus internus), parted by a septum into an upper orifice communicating with the Fallopian aqueduct for the facial nerve, and a lower pit containing minute holes communicating with the labyrinth, and transmitting the filaments of the eighth or auditory nerve.

The lower or third plane surface of the pyramidal process, which is external and connected with the occipital bone, presents, first, at the lower end of the external depression a cartilaginous, rough surface, where it adheres to that bone; then a large sinuous cavity, the jugular notch, forming, with that on the occipital bone, the hole for the exit of the jugular vein, often separated by a bony process into two, the first of which is for the nervus vagus, the second for the jugular vein; a sharp ridge (processus vaginalis) at the base of the styloid process, separating the jugular notch from the glenoid cavity; a circular hole, the external orifice of the carotid canal (canalis caroticus), for the entrance of the internal carotid and the exit of the sixth nerve; a small hole terminating the aqueduct of the cochlea; and, lastly, a rough surface for the attachment of the internal peristophylinus, and the external muscle of the malleus. At the line of junction between this plane and the posterior is generally seen part of the groove for the inferior petrous sinus. (Plate XXVI. fig. 3.)

The circumference is united behind by a serrated margin with the occipital bone; above by a margin, partly serrated, partly imbricated, with the parietal bone and posterior part of the large wing of the sphenoid; and before and below by a serrated margin with the lower part of the same wing. This part, named generally the squamosus, forms with the pyramid a re-entrant angle, in which is received the spinous process of the sphenoid bone; and close beside which is the orifice of the Eustachian tube (iter a palato ad aureen), the canal which leads from the throat to the tympanal cavity. The truncated extremity of the pyramid, which is received by the re-entrant angle formed by the sphenoid and occipital bones, presents the upper opening of the carotid canal, which is imperfect above, and in the recent body is completed by the dura mater.

The temporal bone is thin before and above, where it consists of two tables with intermediate diploe. The mastoid process in the adult consists of numerous communicating cells, lined by very delicate periosteal mucous membrane, continued from the tympanal cavity, with which they communicate. The pyramidal portion is compact and hard, and contains with other parts the labyrinth or internal ear.

Nothing is more interesting than the development of Special the temporal bone. It is ossified in three portions—the large, flat, or squamous; the tympanal ring; the pyramidal, with the mastoid, and the styloid process.

At an early period the pyramidal portion is perfectly formed round the several soft parts, and though porous and spongy, dense bone is seen in the site of the semicircular canals. The different orifices are large and distinct. The tympanal cavity, however, is quite incomplete; and though the carotic canal is formed, the Eustachian tube is in the shape of a mere groove. The size of the pyramid is greater than subsequently in proportion; and the part behind the open tympanal cavity, which is bulky, is to constitute the mastoid process, which however is still a shapeless mass. The squamous portion is thin and almost scaly at birth, with the zygomatic process well marked, and a ring of bone, incomplete at the upper margin, attached to its inferior and posterior part. By this, which afterwards constitutes the ring of the external ear-hole, it is fixed to the pyramidal portion in such manner that the part behind the ring is rather larger and longer than the part before; and the pyramid, instead of projecting, as afterwards, is short and thick. At this period also the flat portion uniting with the occipital bone is not formed, and there is therefore an opening or fontanelle at this point of the cranium. Soon, however, the squamous becomes united with the pyramidal portion; the tympanal ring is fixed to both; the Eustachian tube is completed; and, at the posterior end of the pyramid, bone is deposited and extended in a tabular layer of some thickness. The mastoid process, however, cannot be recognised; and it is only some years after birth (about seven) that a small oblong elevation begins to be visible behind the posterior limb of the auditory ring. If at this time the process is divided, cells of the kind afterwards seen in this part are not distinct; but as its enlargement proceeds, cells begin to be formed about the same time, and at the same rate, as the frontal, ethmoidal, and sphenoidal cells are formed. The figure of the bone also is altered, in consequence of the change which the component parts undergo in relation to each other. The squamous portion expands, the anterior part of the pyramidal portion is elongated and tapers, the posterior and the mastoid parts enlarge, and at a later period the styloid process begins to appear amidst the muscles attached to it.

The temporal bone is united immovably with the sphenoid, parietal, occipital, and malar bones; and the inferior maxillary is connected to it by articulation. In the tympanal cavity, also, are contained the four tympanal bones, to be considered afterwards.

Besides these uniform bones of the cranium, there are occasionally found one or more supernumerary bones, which vary much in number, size, and situation. Most usually they are found in the line between the occipital and parietal bones, causing the lambdoidal suture to vary much in regularity; and occasionally, instead of the apex of the occipital bone, is found a single supernumerary bone. They are observed less frequently at the inferior anterior angle of these bones, and at the temporo-parietal sutures, and still more rarely at the base of the cranium. These bones, to which attention was originally drawn by Wormius, by whose name they are still distinguished (ossa Wormiana), may be regarded as effects of the aberration of the ossic process. Though they have been also named triangular (ossa trigona), their shape is extremely variable. They are similar in structure and mode of union to the parietal and occipital bones; and though they are not entitled to the epithet of cranial keys (clavus crani), often given them, they may be viewed as appendages to the cranial bones, which are then to be regarded as incomplete. The most important fact in their history is, Special that they are most frequent in young subjects, and in Anatomy those in whom ossification is imperfect. As they are rarely found in advanced age, it may be inferred that they eventually become consolidated with one or other of the bones to which they adhere.

§ 5. The Face. (Ossa Faciei.)

The face, situate before and below the cranium, is bounded above by that cavity, on the sides by the zygomatic arches, and behind by a space corresponding to the upper region of the pharynx. Symmetrical in disposition, its anterior surface is trapezoidal, the largest side being above, its vertical section triangular, and each side irregular. The bones of which it consists are those of the upper jaw, comprehending thirteen separate pieces, two superior maxillary bones, two malar bones, two nasal bones, two lacrymal bones, two inferior turbinated bones, two palate bones, and one vomer; and the single lower jaw. (Plate XXVI. fig. 8.)

The superior maxillary bone (os maxillae, maxilla superior) is the basis of those of the upper jaw, and forms a centre-jaw-bone, with which the others are connected. Though in shape irregular, it may be distinguished into zygomatico-facial, orbital, and naso-palatine surfaces. (Fig. 6.)

The zygomatico-facial surface, irregularly convex and concave, consists of two divisions, the facial and zygomatic. The first presents the nasal or ascending process, terminating above in a serrated margin, articulated with the frontal bone; behind in a groove concurring with a similar one in the lacrymal bone to form the lacrymal canal; before by a similar margin joining with the nasal bone; and below, a pit for the insertion of the levator of the upper lip and nose (levator labii superioris alae nasi). The facial region is separated from the zygomatic by a rounded margin, the upper extremity of which is rough and hollowed for articulation with the malar bone (os genae, os jugale); while the posterior forms part of the temporal fossa before, and a distinct protuberance behind corresponding to the posterior part of a large cavity denominated the maxillary (antrum maxillare, sinus maxillaris). This cavity, indeed, corresponds also to the canine fossa and the external protuberance.

The orbital surface, which is flat, and slightly oblique in direction, forming the inner half of the lower wall of the orbit, is bounded within by a sharp line for articulation with the ethmoid bone, without by the rough malar surface, and traversed through its posterior half by a groove for the maxillary vessels and nerve, terminating partly in the sinus, partly in the superior maxillary hole. The posterior margin of this surface, which is obtusely rounded, forms with the sphenoid bone the spheno-maxillary fissure; and its internal or mesial angle is articulated with the ascending process of the palate bone.

The naso-palatine or mesial surface of the bone is complicated. Before and above is seen the inner surface of the nasal or ascending process, traversed by vascular and nervous grooves, and covered by the pituitary membrane. Behind this is the lacrymal groove, terminating in the nasal, which is converted into a canal by the inferior turbinated bone, below which it opens; and the open- ing into the maxillary sinus, large in the detached bone, but contracted below by the inferior turbinate, and behind by the palate-bone. This sinus, which is of an irregular tetrahedral shape, corresponds before to the canine fossa, behind to the zygomatic tuberosity, above to the orbital plate, and below to the alveolar arch. Below this is the palatine plate (apophysis palatina), quadrilateral and horizontal, concave and smooth above, where it forms the lower wall of the nostril, concave and marked by vascular orifices below, where it forms the anterior part of the hard palate. (Fig. 7.) The anterior part of the process is elevated into the nasal spine; its mesial margin, which is thick and marked by numerous grooves, one unusually large for the naso-palatine nerves and vessels (canalis incisivus vel Stemonianus), is joined to that of the opposite side, forming a groove in which the lower margin of the vomer is received; and the posterior, which is thin, is attached to the square plate of the palate-bone, which thus completes the palatine vault.

The palatine is separated from the zygomatic-facial region by a semicircular arch, perforated in the adult by eight honeycomb-like pits (alveoli), in which the roots of the teeth are implanted, and therefore named the alveolar arch. Of these pits the first two are the smallest, the next three larger, and the last three very large,—an arrangement which renders the alveolar arch narrow before, and broad on the sides and behind.

The superior maxillary bone is united, at the points indicated, to that of the opposite side, to the frontal bone, to the ethmoid, to the nasal, to the lacrymal, to the palatine, to the malar, to the inferior turbinate bone, and to the vomer.

It is ossified in one piece. In the fetus its divisions are completely formed, except the orbital plate, the sinus, and the alveoli. In the former, the superior maxillary canal is a slit; and the latter is a mere depression on the nasal surface of the bone. This, however, becomes larger and more capacious, not by excavation, but by the extension of its walls by bony deposition. The alveolar arch in general consists of two parabolic plates united by transverse septa, so imperfect, that the whole intermediate groove communicates freely. These osseous plates are not uniform in number. In some maxillary bones there are four, and a fifth like a mere line at the bottom of the groove; in others six alveoli, viz. four temporary, and two permanent alveoli. These plates are formed by deposition round the dentiferous sacs.

The malar bone (os jugale, os genae) is a quadrilateral bone, approaching the rhomboidal shape, but bounded by curved lines. It presents three surfaces, a facial, an orbital, and a zygomatic; and four angles, a frontal, a temporal, a zygomatic, a superior maxillary, and an inferior maxillary. (Fig. 7 and 8, g.)

The facial surface is convex and smooth, marked by one or two holes (foramen jugale) for vessels and nerves, and, with the zygomatic process gives attachment below to the zygomatic muscles.

The orbital surface, which is concave, directed obliquely upwards, projects backwards from the facial plate, and forms the outer wall of the orbit between the frontal and sphenoid bone above, and the superior maxillary below. It presents the internal malar hole, or the inner orifice of that seen in the facial surface. The posterior edge is rough and serrated for conjunction with the sphenoid bone.

The zygomatic surface is a sort of angular concave recess between the orbital plate above and the facial before, and is chiefly important in forming the anterior part of the temporal fossa. In the angle between the orbital and facial plates is seen a small hole, which communicates with the internal malar above, and the external malar before. The anterior part of this surface is rough, and unites with the external or malar process of the superior maxillary bone.

The superior or frontal angle is serrated for uniting with the external angular process of the frontal bone. The temporal is long and pointed, and rough above, where it joins the temporal bone to form the zygoma, to which the temporal fascia above and the masseter below are attached. The superior maxillary or orbital is also pointed, and joins the rounded ridge at the base of the ascending process of the superior maxillary bone. The inferior maxillary is obtuse-angled, and joins the lower angle of the malar process.

Wedge between the bones of the skull and face, the malar bone is connected to the frontal, the temporal, the sphenoid, and the superior maxillary. It is ossified from a single point.

Each nasal bone (os nasi) is quadrilateral and trapezoidal. Of its two surfaces, the external, smooth and bone, slightly convex, is covered by the periosteum and the pyramidal muscle (compressor narium) and part of the frontal (epicanthus). The inner, rather concave and somewhat irregular, with grooves for vessels and nerves, is covered with the pituitary membrane. (Fig. 8, n.)

The upper margin of the nasal bone, which is somewhat thick, is serrated for union with the frontal bone, on the nasal spine of which it is firmly supported. By the mesial margin, which also is thick, plain, and prolonged backwards, it is joined to that of the opposite side; while its thin external margin being imbricated beneath the mesial one of the maxillary, the central pressure is thus opposed on each side. In this manner the two nasal bones, supported above by the frontal spine, are firmly wedged between the superior maxillary, much on the same principle as the key-stone is wedged between the lateral parts of the arch. (Plate XXIV. 2 and 3, n.) To the lower margin the nasal cartilages are attached. Each nasal bone is formed from a single centre of ossification.

Each lacrymal bone (os lacrymale, os uncus) is about the size of a nail, situate at the inner wall of the orbital bone, occupying the space between the frontal bone above, the ethmoid behind, and the superior maxillary before. Its shape is irregularly quadrilateral, and it presents two surfaces, an orbital and nasal, and four margins.

The orbital surface consists of two regions, one orbital proper, flat, and smooth, situate behind, and connected with the lateral smooth bone (os planum) of the ethmoid, with which it completes the inner wall of the orbit; the other, which is anterior, is at right angles to this, and is moulded into a cylindrical groove, which, with that of the superior maxillary bone, constitutes the lacrymal canal, in which is lodged the membranous tube which conveys the tears and mucus from the eye to the nose. These two surfaces are parted by a sharp longitudinal crest, to which is attached the aponeurosis of the orbicular muscle of the eyelids (orbicularis palpebrarum).

The nasal surface is irregular, covered by the fibromucous membrane of the ethmoid cells, and of which it makes part. It presents distinctly the angle of union between the orbital and lacrymal portion of the bone.

This bone, which is compact, is developed from a single point, and is early formed in the fetus.

The inferior turbinate bones, which are irregular in shape, are attached to the nasal surface of the superior or turbinate maxillary by an oblique line near the lower margin of the ethmum, with the convex surfaces turned to each other.

Each turbinate bone presents a nasal surface, uneven and marked by rough lines, with intermediate cellular grooves; and a maxillary one, concave, and constituting part of the inferior nasal passage. Both are invested by fibro-mucous membrane continued from the pituitary.

Each turbinate bone is bounded by two margins—a superior, which is fixed—an inferior, free. Of the former, the anterior part is a thin border, joining with the superior maxillary bone at the base of the ascending process, and with the lacrimal bone by an angular slip. The middle is a short spinous part, uniting with the lateral mass of the ethmoid, and diminishing the opening of the maxillary sinus; and the posterior part, which is rounded and inclining, is attached to the crest of the palate-bone. The lower margin, which is free, is slightly convoluted on itself, so as to separate the middle from the inferior nasal passage.

The inferior spongy bone, which is formed in one piece, though perforated by vascular and nervous holes, and moulded into cells at its lower convoluted margin, consists, however, chiefly of compact bone. It is covered through its whole extent by the fibro-mucous membrane of the nasal passages.

Each palate-bone (osse palati), attached to the posterior part of the superior maxillary bones, to which they may be regarded as appendages, consists of three parts, a base or palatine portion, a nasal ascending or vertical portion, and an orbital part.

The base consists of a quadrangular and quadrilateral plate of bone, placed horizontally, and attached before to the posterior margin of the horizontal or palatine plate of the superior maxillary bone, and on the inner or mesial side to the corresponding margin of the opposite bone (Plate XXVI. fig. 7, p. p.), with which it forms a groove, in which is lodged the posterior part of the lower margin of the vomer. The upper surface is concave, and, with that of the superior maxillary bone, completes the lower wall of the nasal passages. The lower is almost straight, but presents a slight concavity, bounded behind by a transverse crest of bone, to which the uvula or soft and movable palate is attached. Behind this is a surface bounded by the posterior margin, which is sinuous and lunated, and terminates within in a pointed eminence, which, with that of the opposite side, forms on the mesial plane the palatine spine. The external margin, which rises into the nasal or ascending portion, is rounded without into a sinuous depression, which forms, with the pterygoid process of the sphenoid bone, the pterygo-palatine canal, and which occasionally, at least at its lower extremity, is entirely formed in the palate-bone.

The nasal portion, which is irregular in shape, presents on the nasal surface a hollow, rising from the square plate, and forming the posterior part of the lower nasal passage; a transverse ridge (linea aspera) continuous with that of the superior maxillary bone, and to which the inferior turbinate bone is attached; and then another hollow, forming the posterior end of the middle nasal passage, and with the former contracting the orifice of the maxillary sinus. Immediately above this the vertical portion is parted by a notch into two unequal parts, a posterior articulated with the base of the external pterygoid process, and an anterior articulated before with the superior maxillary bone, and within presenting cells, which unite with those of the ethmoid bone. The outer part of this cellular portion is bounded by three surfaces, one external, forming part of the zygomatic fossa; another anterior, resting on a corresponding surface of the superior maxillary bone; a third superior, forming part of the inner wall of the orbit. The notch between the anterior and posterior divisions forms with the sphenoid bone the spheno-palatine, for transmitting the spheno-palatine twig of the superior maxillary nerve, with some veins, and the internal branch of the spheno-palatine ganglion.

The posterior margin of this vertical portion is acute above, where it is simply conjoined with the base of the pterygoid processes; but below it is moulded into a thick, strong, triangular process, projecting backwards, and marked by three grooves, one in the middle, and one on each side. In the two latter the external and internal pterygoid processes are adapted; and the middle space, being prominent, and firmly wedged between the pterygoid processes, completes the pterygoid fossa.

Each palate-bone is connected with six bones, two of the cranium and four of the face: the ethmoid and sphenoid, the superior maxillary, the inferior turbinate bone, the palate-bone of the opposite side, and the vomer.

The palate-bone, so far as is hitherto observed, is formed in one portion. In the fetus, at the seventh month, it is completely formed; but the square or horizontal part is larger in proportion than the vertical, and remains so till the face begins to alter its shape.

The vomer or plough-share bone is symmetrical, placed on the mesial plane between the sphenoid and ethmoid mer. bones above, and the palate and superior maxillary bones below, and forming the posterior part of the nasal partition.

In shape it is irregular, though it affects the rhomboidal. It consists of two thin plates of compact bone united at an angular line below, but separated above so as to form a deep longitudinal groove, in which the cartilaginous partition before, and the vertical plate of the ethmoid behind, are inserted. At the posterior end these plates spread out into lateral wings with intermediate grooves, in which the azygos process of the sphenoid bone is accurately fitted. These two parts form the upper and posterior margins. The lower consists of a single thin plate, which is received into the linear groove formed by the middle crest of the palate and superior maxillary bones. The anterior part of this margin rises more directly, to fit the nasal spine of the latter bones.

The surfaces of the vomer are smooth, occasionally concave and convex in opposite directions, and, being covered by the fibro-mucous pituitary membrane, constitute the bony partition between the right and left nasal passages. The bone is formed in a single piece, and is generally completed in the seventh and eighth month.

The lower jaw-bone (mandibula, maxilla inferior), nearly parabolic, with an elevated branch at each extremity. It consists of two parts, a maxillary arch, and a ramus at each end, each of which has two surfaces, an external or facial, and an internal or oral, an alveolar or upper margin, and a mental or lower margin. (Fig. 8 and 9.)

The external surface of the parabolic or arched portion of the lower jaw presents first on the mesial plane the symphysial or chin (mentum), indicating the original separation of the bone into two parts,—a vertical line diverging into two, so as to form a triangular eminence (tuber maxillare of Soemmering). (Fig. 8 and 9, x.) On each side of this is a depression for the tuft or elevator of the chin, the anterior mental hole (foramen menti anterius, f), or inferior maxillary for the exit of the third branch of the fifth pair, and the external maxillary line (m) for the insertion of the platysma, depressor anguli oris, and depressor labii inferiores. Behind this the ascending ramus presents a quadrilateral surface, corresponding to the masseter (r), bounded before by a sharp line terminating in the coronoid process (b, b), behind by an obtuse one, the posterior margin terminating in the condyloid or articular process (c, c), and above by the sigmoid notch (incisura semilunaris vel sigmoides) between them. The internal or oral surface of the lower jaw presents in the middle a spine or crest (spina menti interna), consisting in general of three eminences, the two superior of which give attachment to the genio-glossi, and the lower to the genio-hyoidei. On each side of this is a superficial hollow for the sublingual gland, and a pit for the digastric muscle; and extending outward on each side is the internal oblique line, to which the mylo-hyoideus and the superior constrictor of the pharynx are attached. Below this is a depression for the submaxillary gland; behind, at the margin of the ramus, the surface is rough for the insertion of the external pterygoid; between this and the top of the oblique line is the internal mental hole, or the inner orifice of the maxillary canal; and above and round the orifice the surface is rough for the insertion of the internal ligament of the lower jaw. By this orifice the inferior maxillary nerve, or third branch of the fifth pair, with its concomitant vessels, enters the canal; and after sending branches to the alveolar arch and membranes, reappears at the external mental hole.

The upper margin of the parabolic part of the bone is moulded into a series of alveolar or honeycomb-like cavities, bounded by external and internal plates, and separated by septa more or less complete. These cavities are in the adult 16 in number, but are sometimes imperfect, sometimes obliterated by the removal of the teeth. This margin, which, like the corresponding one of the superior jaw, is named the alveolar arch, is, like it, narrow anteriorly, and wide on the sides and behind. At the posterior end of each alveolar arch the external and internal oblique lines form between them a superficial depression, in which part of the buccinator is lodged; and then converging as they ascend, terminate in the pointed coronoid process, to which the tendon of the temporal muscle is fixed, unless at its outer surface, which is covered by the masseter. The condyloid process, separated from this by the sigmoid notch, is broad transversely, and is contracted below so as to form a neck, which is concave within for the insertion of the external pterygoid muscle.

The inferior margin, which is obtusely rounded, and forms a more pointed curve than the upper, gives attachment only to the cutaneous muscle (platysma myoides). The posterior margin, also obtuse, is free, but corresponds to the parotid gland, and is therefore occasionally named the parotid margin. To this the stylo-maxillary ligament is attached.

The posterior part of the bone, named the ramus, forms with its body an obtuse angle of about 100°, which diminishes as life advances. (Fig. 8, a, r.)

The inferior maxillary bone is connected movably with the temporal bone by its condyloid process being lodged in the glenoid cavity of the latter. In this situation it is retained by means of three ligaments, while its motions are facilitated by an interarticular fibro-cartilage.

The external ligament, composed of parallel fibres attached to the tubercle at the bifurcation of the zygomatic process, descends obliquely backwards, and is fixed to the outside of the neck of the condyle of the lower jaw. It is covered by skin and the parotid gland, and is lined by synovial membrane, to part of which the interarticular cartilage is attached. The internal ligament, attached to the spinous process of the sphenoid bone and its vicinity, proceeds obliquely downwards and forwards, between the two pterygoid muscles, expanding to the orifice of the internal maxillary hole, round which it is attached.

The stylo-maxillary ligament is an aponeurotic chord, belonging rather to the stylo-glossus muscle, stretching between the styloid process and the tip of the angle of the lower jaw, where it is inserted between the masseter muscle without, and the internal pterygoid within.

This articulation is so constructed that it possesses two synovial membranes, or at least a double one, the parts of which are separated by the interarticular cartilage. The latter body, which is of an oval shape, convex and concave above, to fit at once the glenoid cavity and the transverse process, but concave below for the maxillary condyle, adheres externally to the external ligament, while its inner margin is free. The upper division of the synovial membrane, therefore, adhering all round to the margins of the glenoid cavity and transverse process, after covering these parts, is reflected from the external lateral ligament over the upper surface of the interarticular fibro-cartilage. A minute slip may be then traced over the free margin of this fibro-cartilage, covering its lower surface, and thence continued over the inside of the external lateral ligament, and from it over the condyle of the lower jaw. In this manner the temporo-maxillary synovial membrane is rather composed of two parts, a superior and inferior, than absolutely double.

The inferior maxillary bone is formed in two pieces; and perhaps no bone in the human body undergoes from first to last greater changes in shape and extent than it does. In the fetus, when first formed, it consists of two slightly incurved portions, united on the mesial plane by cartilage, with the coronoid and condyloid process, and the intermediate sigmoid notch, rising from the posterior extremity of each. The ramus, however, cannot be said to be formed; and it is only some time after birth that the quadrilateral surface by which it is defined can be recognised. At birth, also, the alveolar arch consists only of two thin plates of bone, with scarcely perceptible traces of septa; and the periosteal coverings of the dentiferous sacs are in immediate contact with each other. After birth, bone is deposited between them, so as to form the transverse partitions of the alveoli, which afterwards increase in size and thickness with the bone itself, which enlarges in all its dimensions chiefly by extending backwards. Coalescing by the progress of ossification on the mesial plane, it is a few weeks after birth consolidated into one bone; and after the process of primary dentition commences, it loses the angular and acquires the parabolic shape. About the age of seven, sometimes previously, the body becomes more incurvated, and the posterior extremities enlarge backwards still more rapidly. As the process of secondary dentition advances, these extremities enlarge still more rapidly; and the angle of the jaw acquires a more prominent situation by becoming more depressed. At the time at which the facial and maxillary sinuses are formed, and the superior maxillary bone extends backwards to form its tuberosity, the posterior extremity gradually rises in the form of the ramus, till this part a year or two after puberty is fully an inch above the plane of the alveolar arch. During adolescence and middle life this is the condition of the jaw-bone. Towards the decline, however, the teeth drop out, and the alveolar processes are absorbed; and in old age the lower jaw consists often of a single cylindrical arch of bone placed between its two rami, which, retaining their original breadth and height, necessarily throw the body of the bone forwards beyond the upper alveolar arch.

The lower jaw-bone consists of two plates of compact bone, with cancellated tissue interposed, and traversed by the inferior dental canal, the walls of which, like the surface of the bone, are compact. This canal is subdivided into two parts,—one inferior, which terminates in the anterior mental hole, transmitting the mental branch of the inferior maxillary nerve; the other superior, which is parted into numerous minute passages into the cancelli of the bone and alveolar processes. These, it must also Special be observed, consist of a peculiar form of cancellated structure. Externally their bony walls are perforated by numerous minute well-defined holes, into which, in the recent state, the vessels and filaments of the alveolar periosteum penetrate. These orifices are so numerous in both maxillary bones, that a portion of alveolar process held between the eye and the light seems entirely perforated, and, if injected, becomes completely red. This character applies chiefly to the period of youth and adolescence. After this the alveolar processes become more solid, and eventually present much fewer orifices. This structure is the result of the manner in which the bony matter is deposited round the vessels and filaments of the periosteum, which may in this and similar bones be said to communicate in this manner with those of the medullary membrane.

The Teeth. (Dentes.)

The teeth, which are implanted in the alveolar cavities, though belonging properly to the digestive apparatus as organs of mastication, are nevertheless more conveniently considered in this place. (Plate XXVI. fig. 7, 8, and 9.)

In every tooth are recognised three parts,—the crown (corona), the neck or collar (collum), and the root (radix). The first is the portion which appears above the gum and alveolar process, and consists of a layer of enamel, thick above and round the top, but gradually attenuated below, inclosing a small portion of compact bone. The crown may be distinguished into the crown proper, or the summit or apex of the tooth, and the fillet or annular portion of enamel (annulus) by which the sides are surrounded. The root, which consists of compact bone, is the part which is implanted in the alveolar cavity, and the outer surface of which adheres to the inner or dental surface of the alveolar periosteum, and above that to the soft part of the gum. The neck is the narrow ring where the enamel ceases and the bone begins, and to which the gum adheres all round. This part, in short, belongs neither to the crown nor to the root, and perhaps is not justly entitled to any separate consideration, unless as the portion to which the gum adheres. The crown and root, on the contrary, are important, as furnishing the characters by which the teeth are distinguished into classes.

These are three,—the incisor or cutting teeth (dentes tonici, incisores, primores, risorii, acuti, adversi); the canine or tearing teeth (dentes canini, lanarii, cuspidati); and the molar or grinding teeth (dentes molares).

The incisors are in number eight, four in each jaw, and two on each side of the mesial plane. All of them agree in having the crown or apex wedge-shaped, or like a carpenter's adze, convex before, and slightly concave behind, with the cutting edge crenated or notched. From the edge, also, which is broad, the fillet, which is quadrilateral, contracts much to the neck; and the root is bevelled in the opposite direction to that of the crown, so as to form a quadrilateral prism, and slightly acuminate. It is always simple and elongated. Its extremity presents an orifice communicating with the interior of the tooth, and admitting the vessels by which it is nourished. The crown is separated from the root by a narrow line, varying in position in the different kinds of incisors.

The incisors of the upper jaw are broader, thicker, longer, and in general more powerful, than those of the lower, and their axes are directed downwards and forwards so as to overlap in the motions of the lower jaw those of the inferior row, and leave a triangular interval with the base upwards. Their cutting edge also is oblique, so that its mesial angle is longer than its external; and their roots are larger and rounder. The central or middle incisors are larger, broader, and stronger, than the lateral ones.

The incisors of the lower jaw are smaller than those of the upper, and their axes are directed upwards and backwards, so that they are within the superior incisors. The central incisors also are larger than the lateral ones.

The canine or pointed teeth (dentes cuspidati) are four in number, one in each half of each alveolar arch, immediately next to the lateral incisors. These teeth are distinguished by prominent, thick crowns, with rounded convex fillets and pointed apices. The root also, which, like that of the incisors, is simple, is larger and thicker than in the latter. The upper canine teeth, which occasionally are named eye-teeth (oculare dentes), are the longest and most prominent of all. During the elevation of the lower jaw, each inferior canine tooth is inferior to the superior one, and is interposed between it and the lateral incisor.

Of the molar or grinders there are 20 altogether, being five in each half of each alveolar arch. They are subdivided into two orders, small molar or bicuspid teeth (dentes bicuspidati), and large molar or multicuspid teeth (dentes multicuspidati).

The molar teeth agree in having large, broad crowns, with tubercular summits, and roots, which, though occasionally single, are much more frequently two-fold, three-fold, or four-fold. The coronal tubercles are generally parted by a deep furrow, which gradually becomes shallow as the summits wear in the progress of years. When the roots are single, which is most frequent in the bicuspid order, each lateral surface is marked by a longitudinal furrow. When two-fold or manifold, they are parted by a fissure of variable width; and sometimes they diverge considerably. The annular furrow between the crown and root is very distinct.

The axes of the upper molar teeth are directed outwards, while those of the lower order, especially the most posterior, are directed inwards. More anteriorly they are occasionally vertical.

The two molar teeth next to the canine, which have smaller crowns and roots, and are less in all their dimensions than the three posterior ones, are therefore distinguished as small molars. From the circumstance of their crowns being provided with two conical apices, one anterior, large, and the other posterior, parted by a transverse furrow, not dissimilar to the summits of two canine teeth conjoined in one, they were denominated by John Hunter bicuspid teeth (bicuspidati). These teeth are smaller than the canine, especially when their roots are single. The roots, however, are often bifid, and sometimes trifid. In the first case they are bevelled on the sides, and terminate in a point. In the second and third case they are conical. The internal surface of the bicuspid teeth is very generally narrower than the external, so that a transverse section would be trapezoidal, with the narrow margin posterior.

The third molar tooth, or the first large molar, is generally very large and strong, with the crown broad and quadrilateral, surmounted by four, five, or more tubercles, and the root trifid or quadrifid and divergent in the upper tooth, more frequently bifid only and divergent in the lower. The second large molar tooth, though rarely so large as the first, has the same general shape; the crown rhomboidal in the upper jaw, with four apices, and the root bifid or trifid and divergent.

The third large molar, named also wisdom-tooth (dens sapientiae), from its late appearance, is smaller than the second, generally has a narrower crown, rounded, oblong, quadrilateral, or rhomboidal, with two or three apices, and a narrow root generally single and conical, often incomplete. Its axis is strongly directed inwards, especially in the upper jaw.

The teeth now enumerated constitute arches of a parabolic or semielliptical shape, larger in general in the upper jaw than in the lower. In the upper arch especially, the curvature is more rounded or elliptic; in the lower it is more angular and parabolic—a circumstance which, with the different directions of the axes of the incisor and molar teeth respectively, causes the upper incisors to overlap, and thereby cut upon the lower ones, while the molars are fitted to each other so as to move on mutual surfaces in the lateral motion of the jaw.

The teeth vary in number, shape, and position.

Though the general number of the adult or permanent teeth is 16 in each jaw, or 32 in all, it may happen that, in consequence of all the wisdom-teeth not coming through the gum, there are only 28 or 30. Occasionally also the lateral incisors are wanting. In some rare instances there is a supernumerary incisor or molar tooth; and Soemmerring mentions an instance in which, by the addition of four molar teeth, the total number was augmented to 36. The union of two or more teeth into one is occasionally observed.

The most usual variations in shape are observed in the incisors being excessively large and broad, in the canine being very thick and long, ascending into the antrum, and in some rare instances extremely small. In females the canine teeth are occasionally so small and rounded, that they have the appearance rather of rudiments than of perfect teeth. The cleft roots of the molar teeth are liable to very great varieties in shape.

The most usual variety in position is when the incisors are placed obliquely, with their margins not lateral but antero-posterior. This is in general the result of the teeth being too much crowded in a small alveolar arch; and the malposition is always greatest as the jaw is narrow, or imperfectly formed. One or two incisors even in such circumstances may be entirely behind or before the rest, so as to give the appearance of a double row. The canine teeth are liable to the same change of position; but one greatly more frequent with them is, to be placed so much before the line of the arch as to project considerably forwards, like the tusks of some animals. Another form of this variety is, when teeth appear in unusual situations, for instance the palate or pharynx, or even in the orbit.

The teeth are not at all periods of life the same in number. Generally speaking, at birth, when the teeth have not appeared above the gum, the rudiments of five teeth are found in each half alveolar arch. These, which are to constitute the milk-teeth, the deciduous or temporary, appear above the gum nearly in the following order: the central incisors of the lower jaw about the end of the sixth or beginning of the seventh month; a few weeks after, the central incisors of the upper jaw; after these, the lateral incisors above or below, without determinate order; and between the 12th and 18th months the first pair of molars, either above or below. These are followed by the lower canine teeth, and about the second year by the upper canine teeth. About the end of the second year, or in the course of the third, the second pair of molar teeth cut the gum; and about the fourth or fifth year in general, the third pair of molar teeth appear. The following table of the periods at which the different classes of temporary teeth appear, given by Mr Thomas Bell, may communicate a general idea of the succession.

| Periods | Teeth | |------------------|--------------------------------| | From 5 to 8 months | the 4 central incisors | | From 7 to 10 | the 4 lateral incisors | | From 12 to 16 | the 4 anterior molars | | From 14 to 20 | the 4 canine | | From 18 to 36 | the 4 posterior molars |

From these periods, however, there are extensive exceptions; and in no two individuals even of the same family does the same tooth appear at the same period.

About the seventh month the milk-teeth begin to appear above the gum; and about the seventh year they begin to be shed and succeeded by the permanent set. This process begins also in the lower jaw, and advances nearly in the same order: the lower central incisors; the upper, and the lateral above and below; the first pair of molar upper and lower; the second pair of molar above and below; the canine above and below; the third pair of molar; the fourth pair of molar in the eighteenth year; and the fifth pair, or wisdom-teeth, in the eighteenth, twentieth, or thirtieth years.

The average periods of eruption in the lower jaw are given in the tabular form by Mr Thomas Bell, in the following order.

- The anterior larger molars ........................................... 6½ years. - The central incisors .................................................. 7 - The lateral incisors .................................................... 8 - The anterior bicuspids .................................................. 9 - The posterior bicuspids ................................................ 10 - The canine or cuspidati ................................................ 11—12 - The second large molars ............................................... 12—13 - The third large molars, or wisdom-teeth ......................... 17—19

Those of the upper jaw are understood to follow these at an interval of two or three months.

In structure the teeth of the human subject belong to the order of simple teeth, that is, consist of bone, invested at the crown by enamel.

The hyoid bone (os hyoides, &c., ossa lingualia), though entirely unconnected with the skeleton, yet as a bone to which are attached various muscles of the throat, must be noticed in this place. It is a bone, or rather a bony apparatus, consisting of five separate pieces, arranged in the parabolic form, and articulated movably with each other. These five pieces are, one middle, two lateral, and two piform bones.

The middle (os medium linguae), named also the body, is large, broad, and square, with the anterior surface in general convex and rough, divided by a middle ridge into right and left halves, and by a horizontal line into upper and lower parts, and giving attachment on each side of the middle crest to the digastric, the stylo-hyoid, the mylo-hyoid, the genio-hyoid, and the hyoglossal muscles. The posterior surface is concave and smooth, and covered by cellular tissue, connecting it to the epiglottis. To its inferior margin, which is more extensive and irregular than the superior, are attached externally the sterno-hyoid, the omo-hyoid, and the thyro-hyoid muscles; and in the middle the thyro-hyoid membrane. To its upper margin the fibres of the hyoglossus are attached. Each of the lateral margins is moulded into a convex cartilaginous surface, articulated with the lateral bones.

The lateral bones (ossa lateralia, cornua), though longer, are less thick than the body. Broad and thick before, with the upper surface concave and the lower convex, narrow behind, they terminate in a round head, tipped with cartilage, to which the thyro-hyoid ligament is attached. At the anterior junction nearly of these with the middle portion, there is attached to the latter on each side a small elongated bone, somewhat hooked. These bones, which seldom exceed the size of a grain of wheat, or rye rather, and which they somewhat resemble in Special shape, are articulated to the other two by a true capsular ligament. To their outer surface are attached some fibres of the genio-glossus, and to their upper is fixed the stylo-hyoid ligament.

The hyoid bone consists externally of compact, and internally of cancellated tissue, the latter being most abundant in the middle piece. Though composed in the infant and young subject of five portions, the articulations are invariably obliterated by ankylosis in adult life, and they are converted into a single bone. The junction of the middle and lateral portions is effected first, and that of the pisiform bones afterwards.

The bones now described, excepting the lower jaw and hyoid, are united immovably, or by synarthrosis. The external shape of the cranium is that of an oblong spheroid, or an ovoid, with the small diameter before. Convex in general, it is flattened laterally in the temporal regions, and below in the base. The external surface, smooth and regular above, is marked below by muscular impressions, and penetrated by numerous holes.

The first objects deserving attention are the serrated lines of junction, or what are named the sutures (suturae), which are in general more conspicuous externally than internally, where indeed they are effaced at an earlier period of life than on the outer surface of the skull. The sutures may be most easily understood by tracing them from the sphenoid bone, which may be regarded as the central point of the cranium.

The first line is that which passes transversely across at the junction of the sphenoid with the ethmoid and superior turbinate bones in the middle, and the frontal bone on each side. Concave in the middle, this line bends backward at each extremity, where it follows the outline of the small wings of Ingrassias. It constitutes the transverse or sphenooidal suture.

The posterior margin of the body of the sphenoid bone is marked by another transverse suture, extremely short, and uniting it with the eminence process of the occipital bone. This, which is early obliterated by the indissoluble union of the sphenoid and occipital bones, is a cartilaginous junction, afterwards ossified, and, though scarcely entitled to the epithet, is named nevertheless the basilar suture.

A more distinct one is found in the line between the exterior concave margin of the large wing of Ingrassias and the squamous portion of the temporal bone in the spheno-temporal suture. It terminates below at the glenoid fissure, forming an acute angle with a short line between the pyramid and the posterior margin of the spinous process of the sphenoid, named the petro-sphenoidal. Above, where it terminates on the parietal bone, a short line, between the outer margin of the large wing of Ingrassias and short spaces of the parietal and frontal bones, is distinguished as the lateral sphenoideal or the spheno-parietal suture.

This line, produced backwards between the upper margin of the temporal and the lower margin of the parietal bone, constitutes a peculiar form of junction, named the squamosal suture (sutura squamosa), the temporal, or the temporo-parietal, in which the edge of the former bone is imbricated over that of the latter. In this mode of junction, which is confined to the superior part of the temporal bone, and in which the union of the bones is not secured by dove-tail ossification, but simple imposition, the lateral pressure is effected chiefly by the force propagated from the zygoma and the malar bone.

The posterior part, which is united to the posterior-inferior angle of the parietal, and the anterior-inferior margin of the occipital, presents a serrated line, with alternate indentations, which are well marked, but irregular in size. This, which occasionally presents Wormian bones, may be named the posterior-temporal suture. The Cranium descending portion has been distinguished by the name of mastoid suture. Anteriorly, in the base of the cranium, where it passes the jugular notch, the line of junction, which is cartilaginous, is termed the petro-occipital suture.

The sutures now enumerated agree in being found chiefly at the lower region of the cranium, and in securing the junctions of its base. The others to be yet enumerated belong to its superior region, and agree in consolidating and securing the several arches which constitute what may be named the vault of the cranium.

From the point at which the posterior, temporal, and mastoid sutures unite, a serrated line of junction ascends on each side to the common point at which the occipital and parietal bones meet. From the angular junction formed by the two limbs of this suture, it is known under the name of lambdoidal (sutura lambdoidalis); and from its situation it is termed the occipital and occipito-parietal suture. By mutual indentations, which are always distinct, it joins firmly the parietal and occipital bones; and it is the most frequent seat of Wormian bones.

From the angle of the lambdoidal suture a similar serrated line proceeds, uniting the two parietal bones on the mesial plane, with equally distinct indentations. The mode in which this stretches between the lambdoidal and coronal sutures, bearing some remote resemblance to an arrow on the drawn bow-string, has procured it the name of the sagittal (sutura sagittalis). In youth and in early life these two sutures are distinct; but in advanced age they are more or less, sometimes entirely, obliterated.

In some craniums the sagittal suture is continued along the frontal bone to the nasal spine, thus parting the bone in two lateral halves. This, which constitutes the proper frontal or median suture, is the remains of the original separation of the bone.

Lastly, Between the frontal bone before, and the parietal bones behind, is seen a serrated line crossing the cranium transversely, the whole breadth between the two sphenoideal bones. This, which is named the coronal suture, presents large indentations on each side and small ones in the middle, on the external table, and a converse arrangement on the internal.

By these sutures the bones forming the vault of the cranium are firmly secured; and each bone is made to press against the other so as to augment rather than diminish strength.

The external surface of the cranium may be distinguished into four regions, a superior, an inferior, and two lateral ones.

The superior region, or the vault, is bounded before and behind by the nasal and occipital protuberances, and on each side by the temporal arches. It presents, besides the coronal, sagittal, and lambdoidal sutures, the superciliary arches, the frontal, parietal, and occipital protuberances, and the parietal holes. It is covered by the epipranial muscle and its aponeurosis.

The inferior region or base, which may be defined from the occipital protuberance behind to the nasal spine before, is free as far as the pterygoid processes of the sphenoid bone, anterior to which it is joined to the bones of the face.

In the posterior portion are seen the occipital spine and muscular impressions, the occipital hole (foramen magnum), the condyloid processes, the anterior and posterior condyloid holes, and the basilar process. Laterally are the digastric groove, the mastoid, styloid, and vaginal pro- cesses, and the stylo-mastoid hole, the glenoid cavity and fissure; the jugular hole (foramen lacrimum in basi crani), separated by a bony process into an internal part for the nervus vagus and the accessory nerve, and an external for the jugular vein; the pyramid, with the carotid canal, and the anterior lacerated hole between its extremity, the basilar process, and the sphenoid bone, closed by fibrocartilage in the recent subject. Before these objects, and nearly in the same transverse line, are seen the anterior half of the glenoid cavity of the temporal bone, the guttural orifice of the Eustachian tube, the spinous and elliptical holes of the sphenoid (Plate XXIV. fig. 5), and the pterygoid processes.

The anterior portion presents the crest or azigos process united with the vomer and ethmoidal plate, the sphenoidal sinuses, the ethmoidal bone itself, and the nasal spine of the frontal bone; laterally, the anterior surface of the pterygoid processes, the Vidian canal, the round or superior maxillary hole, the temporal and orbital surfaces of the large wings of the sphenoid bone, the spheno-ethmoidal fissure (foramen lacrimum), the optic holes, and the small wings of Ingrassia; and, lastly, the vault and internal wall of the orbit, the former by the frontal bone, the latter by the os planum and lacrymal bone.

The lateral regions of the cranium are nearly of an elliptical shape. Each region may be circumscribed by a line drawn from the mastoid process backwards to the union of the temporal and mastoid sutures, then following the semicircular arch of the parietal bone, and the angular arch of the frontal to the zygoma, ear-hole, and mastoid process. The objects inclosed in this region are the posterior mastoid hole, the mastoid process, the ear-hole, and the zygoma, with a large space, defined by the elevated line extending from the posterior extremity of the zygoma upwards to the semicircular arch of the parietal bone, where it is obtuse, and the external angular ridge of the frontal bone, where it becomes acute. To this line, the zygoma, and the malar bone, the fascia of the temporal muscle is firmly attached; the muscular fibres adhere to the bone below as far as the line of the sphenoid bone, and pass downwards under the zygoma. The whole region, though convex in early life, becomes less so in adolescence, and in manhood and advanced age it is flattened and even hollowed.

The internal surface of the cranium, lined by the dura mater, and marked by cerebral and vascular impressions, is distinguished into the superior region or vault, and the inferior or base.

In the former, which is a regular spheroidal concave, the chief peculiarities are, on the mesial plane, the frontal crest, the sagittal groove for the superior longitudinal sinus, pits for the granules of Pacchioni, and the inside of the sagittal suture, more distinct than the outside; laterally, the upper cerebral regions of the frontal and parietal bones, with their fossae, the coronal suture, and the superior occipital fossa.

The base is more complicated, and is generally distinguished not only into lateral halves, but into anterior, middle, and posterior regions.

On the median line from before backwards, the objects are,—the blind hole (foramen cecum), for the naso-frontal vessels; the ethmoidal crest (crista galli), and vertical plate, with the perforated plate (e); the spheno-ethmoidal suture; the transverse groove and olivary process, and optic holes (1.1); the pituitary fossa (epiphysium) (3); the posterior clinoid processes (4.4); the spheno-occipital junction; the basilar groove for the medulla oblongata (6); the occipital hole; and the internal occipital spine and protuberance. (Plate XXIV. fig. 6.)

Of the lateral halves, the anterior or frontal region is bounded before by an indistinct curved line, formed by the vertical with the horizontal table of the frontal bone, and behind by the sphenoidal arch. In this, which is named the frontal fossa, the anterior lobe of the brain is lodged; while the sphenoidal arch enters the fissure of Sylvius.

Between the sphenoidal arch before, and the posterior margin of the temporal pyramid behind, is contained a cavity shaped like a spherical segment. In this, which may be named the spheno-temporal hollow (fossa spheno-temporalis), the anterior part of the posterior lobe of the brain is lodged. In this cavity also are seen the spheno-ethmoidal fissure; the round or superior maxillary hole; the oval or inferior maxillary hole; the spinous or meningeal hole, with the meningeal groove; the anterior or spheno-temporal fissure (foramen lacrimum anterius basis crani); the inner end of the carotid canal; the pyramidal groove; and the seminal fossa for the Gasserian ganglion. (Plate XXIV. fig. 6.)

Between the temporal pyramid and the internal occipital spine is contained the posterior or temporo-occipital hollow (fossa temporo-occipitalis), which is further subdivided into two cavities, the cerebral above, and the cerebellar below. From the posterior margin of the pyramid to the transverse occipital ridge, a fold of the dura mater, stretched horizontally, separates the temporo-occipital cavity into a superior for lodging the posterior lobe of the brain, and an inferior or cerebellar for lodging the lobes of the cerebellum. In the anterior or cerebellar division is seen the posterior surface of the pyramid, with the internal auditory hole, the orifice of the cochlear aqueduct, the groove for the lateral sinus terminating in the jugular opening, the groove of the inferior petrous sinus, and the mastoid hole and suture. The only object behind is the posterior cerebral fossa, traversed by the lambdoidal suture.

In the fetus the cranial bones inclosed between the Develop-pericranium and dura mater, which are thick, soft, and ment and vascular, are incomplete shells not in contact with each other, with prominent and rather thick ossific centres, from which the osseous radii diverge, and terminate in thin, ciliated margins. At birth, and for some weeks after, though ossification is far advanced, the margins of the bones are incomplete, so as to form the open spaces denominated fontanelles. Of these there are six at the period of birth; the anterior or rhomboidal between the frontal and parietal bones; the posterior or triangular between the occipital and parietal bones; two lateral anterior between the parietal, spheno-ethmoidal, and temporal bones; and two posterior lateral between the parietal, temporal, and occipital bones, both of irregular shape. At these points the motions of the brain are distinctly felt.

At the same time the bones have not yet acquired their serrated margins, so that the places of the sutures, which are not yet formed, are occupied by narrow grooves between the cranial bones. As ossification advances, however, their fibrilated margins extend, and mutually meeting, are prolonged so as to be indented into each other by alternate notches and processes. At the same time the bones acquire thickness, so that a distinct space is perceived between the external and internal surface of each. The alternate processes and notches thus acquire firmness, and are immovably dovetailed into each other. In this manner the anterior angles of the parietal bones unite with the frontal, and between the posterior ones the apex of the occipital bone is gradually mortised.

In some instances, however, where the ossific centre of the original bone appears deficient in energy, or tardy in progress, a new centre may be developed in the line of Special junction, while the bones are still much apart. Thus, between the occipital and parietal bones, or between the occipital and temporal bones, may be developed new centres, from which ossification advances, as from the principal points, towards the circumference; and by the successive deposition of bony matter, the margins begin to meet those of the primary bones. The process of mutual indentation takes place exactly in the same manner as with the primary bones; and by this means secondary bones are formed in the lines of the sutures.

The period at which the cranium is entirely ossified varies in different individuals. In general the anterior or fronto-parietal fontanelle, which is the largest, is ossified at the end of the 18th or 20th month, while the anterior and posterior lateral are closed at an earlier period. In some instances, however, between the parietal and frontal bones a small space is left till the 6th or 7th year; and in many persons the part continues depressed and tender for the greater part of life. The sutures are completed at the same time, and are always distinctly formed by the 10th or 11th year. A few years after, they become more consolidated, and, as the bones acquire thickness and density by the compactness of the external and internal tables, are firmly wedged into each other. The spheno-basilar junction generally remains soft and separable till adult age, when by its union the sphenoid and occipital bones are converted into a single piece. Some time afterwards the sphenoid is united with the ethmoid, the two parietales are converted into one, and occasionally one or both are united to the frontal bone. In advanced age many of the sutures disappear entirely, at least in one surface of the cranium, generally the internal first; and the cranium would be converted into a single bone if life were continued sufficiently long.

In shape and dimensions the cranium varies at different periods of life. After ossification is completed in the child, the prominence of the osseous points, which continue more or less conspicuous till manhood and the formation of the frontal sinuses, gives it a cubo-spheroïdal shape. Its section is an oval or two hemispherical segments, the anterior being the smallest. At this period the parietal tuberosities and the occipital eminence are prominent, the frontal bone is vaulted, and the high open forehead communicates to the countenance an expression of beauty and simplicity which are always associated with the early and middle periods of life. In the progress of years, however, these prominences become less distinct, partly by the operation of muscular action, partly by the uniform rising and swelling of the margins of all the bones; and the anterior upper and posterior part acquires a uniform spheroïdal or vaulted appearance, while the lateral regions are flattened by the action of the temporal muscles. The occipital region also below the spine is flattened, and occasionally excavated; so that while the spine is prominent and unifrom, the base is excavated, and overhung by the mastoid processes and the semilunar ridges. The aged skull is thus distinguished by a general roundness or ovoidal character, unless in the temples, which are flat and hollow; and the convex but occasionally depressed forehead indicates in some degree the transition from youth to age.

The dimensions of the cranium are estimated from its diameters, longitudinal, transverse, and vertical. The first, which extends from the foramen cecum of the frontal bone, is about five inches at an average. The largest transverse diameter, which extends between the bases of the temporal pyramids, is about 4½ inches; and a smaller one between the extremities of the two small sphenoidal wings is about 3 inches and 9 lines. The longest vertical diameter, which is between the anterior margin of the occipital hole and the middle of the sagittal suture, varies from 4 inches to 4 inches and 3 lines. From these measurements it results, that the most capacious part of the skull is nearly at the union of the two anterior thirds with the posterior, viz., the level of the occipital hole and basilar groove; and that the ovoidal or oblong-spheroïdal is the most general shape. The variations from this shape are found chiefly in the vault, which may be flattened, oblong, cuboidal, or conical.

The Asio-European may be regarded as the best and most symmetrical shape, and to this most of the European crania belong. According to Soemmerring, the Belgic skull is the most oblong-globular, the German and Italian spherical, and the Turkish the most spherical of the European. In this country the most usual shape is the oblong-spheroïdal, especially among the inhabitants of England. Among an extensive collection of skulls preserved in the Museum of the University of Edinburgh, and believed to be chiefly Parisian, the prevalent shape is the oblong-spheroïdal, and the globular, or the general spherical shape, with large transverse diameter approaching to the longitudinal. From the delineations given by Sandifort (Museum Anatomicum, tom. ii.), the English appears most prominent in the occipital region, the French the most vertical forehead, and the Italian most elevated in the vertical region, and most prominent between the parietal tuberosities. The skull of the Swede approaches the cubo-spheroïdal, and that of the Russ is distinguished chiefly for the vertical front, considerable transverse width, and large cheek-bones. The latter appear not to be peculiar to the Scotch cranium.

Of the Asiatic crania, the Tartar has the forehead large, not much arched, the occipital region large, the nasal bones descending straight from the frontal, the upper maxillary bone slightly overhanging the lower, and the chin prominent. That of the Calmuc has the vertical, occipital, and parietal regions prominent, the frontal bone and face flattened, the cheek-bones large, and the alveolar arches and jaws broad and prominent. The Mongolian is distinguished by the narrow forehead, flattened and rather depressed glabellar and nasal regions, great facial width between the cheek-bones, and prominent upper jaw.

From the observations of Blumenbach and Soemmerring it results, that the ancient Egyptian or Coptic head, as exemplified in mummies, belongs to the European class of crania. The negro head, on the contrary, is distinguished for its oblique forehead, compressed sides, prominent jaws, general wedged shape, and large size compared with the rest of the skeleton. For more minute information on these varieties, the reader will consult with advantage the work of Soemmerring (tom. i.), and the Decades Craniorum of Blumenbach.

In shape the face forms an irregular hexahedron, with the large excavation at its lower region for the mouth and generally-pharynx. Its anterior surface is trapezoidal, with the short side below; its sides trapezoidal, with the short side formed by the posterior margin of the maxillary ramus; and its upper surface is an oblique parallelogram.

The greatest transverse diameter is between the zygomatic angles of the cheek-bones, varying from 4½ to 5 inches; its smallest at the symphysis of the lower jaw, from 1½ to 2 or 2½ inches; and on the extent and prominence of which depends the general oval shape of the countenance. The height, measured from the glabella to the triangular process of the lower jaw, varies from 4½ to 4 inches 9 lines.

The direction of the face varies according to the position of the lower jaw. When this is horizontal, the facial plane forms with it an angle of 60°; or deviates 30° from the vertical plane; and in some tribes, as the negro, this deviation is still greater. A more important character, however, is believed to be found by determining the direction of the face in relation to that of the cranium, or ascertaining what Camper denominates the facial angle. This he proposes to fix by drawing one line from the frontonasal protuberance to the spine of the upper maxillary bone—the facial (linea facialis); another transversely between the external ear-holes; and from the latter a third line (linea horizontalis), drawn at right angles to meet the first. The angle thus formed by the facial and horizontal lines, which is termed the facial, indicates the comparative prominence of the cranium and face. In European heads generally it is about 80°; in the negro it is not above 70°; and in the Mongolian, which is intermediate, it is about 75°. The effect of this angle in giving the countenance intellectual expression, the nearer it approaches to the rectangle, was known to the ancients. In many of the busts of heroes it is almost 90°, and in those of divinities 100°; and as we know that this is much more rectangular than any specimen of the human skull furnishes, it may be inferred that it is imaginary.

It may be further observed, that in the infant the facial angle approaches to 90°, in consequence of the small relative development of the face. Towards boyhood and puberty, when the face acquires greater size and prominence, it diminishes to 85° and 80° successively. (Cuvier, Bichat.)

The face is subdivided into cranial, facial, zygomatic, and palato-maxillary regions. It is unnecessary to enumerate again the objects found in these several regions; but it is requisite to consider shortly the cavities which are formed by the cranio-facial bones. They consist of the nasal cavities, the orbits, the tympanal cavity, and the palato-maxillary region. These cavities are distinguished by the following circumstances. All of them communicate mutually, and are covered by fibro-mucous membrane, also continuous. In each of them is lodged one of the organs of special sensation; and each communicates with the cranial cavity by openings, through which nerves always, and sometimes vessels, are transmitted. Lastly, these cavities may be regarded as the points by which the cutaneous surface communicates directly with the mucous membrane of the gastro-pulmonary organs.

The nasal cavities (cavum nasale, nares), of an irregular quadrilateral shape, consist of four regions; the upper, the lower, and two lateral. The first is bounded before by the nasal bones, behind by the sphenoidal cells, with which it communicates, and above by the cribriform plate; while its lower limit is a line uniting the inferior margins of the lateral portions of the ethmoid bone. This is parted by the vertical plate of the ethmoid bone into two halves, which are the two superior passages (meatus superior). The lower region is bounded below by the palato-maxillary plate; on the sides by the maxillary, palate, and inferior turbinated bones; above by a plane uniting the lower margins of these bones, and is parted into two by the vomer, which opens before at the nasal notch of the maxillary bones, and behind at the posterior margin of the palate bones. This constitutes the lower passage (meatus inferior), at the anterior extremity of which the nasal canal opens. The anterior part of the region presents on the mesial plane a vertical triangular notch between the middle ethmoid plate above and the vomer below, occupied in the recent subject by the cartilaginous septum of the nose. The middle and lateral regions, which communicate before by this notch, are separated behind by the ethmoid plate and vomer, and are bounded above by the ethmoidal turbinated bone, and below by the maxillary turbinated bone. This constitutes the middle canal (meatus medius), in which the frontal and maxillary sinuses open.

These cavities communicate freely with each other; their parietes are covered by continuations of the same general fibro-mucous membrane. Their use appears to be to increase the extent without adding to the weight of the facial bones, to afford great superficial extent to the nasal membrane as an organ of smell, and to afford a sonorous vault to the organ of voice.

These cavities, and their appendages, do not exist in the fetus, nor for some time after birth. The ethmoidal and sphenoidal are early formed; and the maxillary sinus begins to be manifest some months after birth. After the primary dentition they enlarge, and rapidly after the second; and towards the approach of puberty, when the maxillary tuberosity is formed, they increase, and speedily attain their natural capacity.

The orbits are two cavities, one on each side of the median plane, of the shape of a quadrilateral pyramid, with the apex towards the cranial cavity, and the base anteriortly. Each orbit presents a vault formed by the frontal bone, a floor formed by the superior maxillary, an internal wall formed by the palate bone, ethmoid, and lacrimal, and an external wall formed by the malar and sphenoid bones. The two internal walls are nearly parallel,—an arrangement which renders the axes of the orbits convergent backwards, and indefinitely divergent before. The vault of the orbit is so thin, that a pointed instrument easily penetrates; and a thrust in the eye is invariably attended with severe, generally fatal, injury to the base of the brain. The base of the orbits is oblique, with the temporal margin behind the plane of the nasal, making the eye more exposed without than on the mesial side. The inner or nasal margin presents the upper orifice of the nasal canal. At the posterior extremity of the inner wall is the optic hole; at the apex is the sphenoidal fissure, which forms nearly a right angle with the spheno-maxillary fissure below; and the floor is traversed by the superior maxillary fissure and canal. The apex of the orbit is occupied by the optic nerve, the third and fourth pair, the ophthalmic branch of the fifth, and the sixth; and the origins of the six muscles of the eyeball, with interposed fat. The base is occupied by the eyeball, surrounded with the tendinous extremities of the muscles, the lacrimal gland at the external region of the vault, and the lacrimal sac in the anterior depression of the nasal margin. To its margins are attached the palpebral and the orbicular muscle. Each orbit communicates with the nasal cavities by means of the nasal duct.

The tympanal cavity, formed in the temporal bone, communicates by the Eustachian tube with the posterior part of the nasal and palato-maxillary cavities. Its further examination belongs to a subsequent head.

The palato-maxillary cavity is formed by the palatine vault above, the alveolar arches and teeth before, by the lower jaw before and laterally, and behind by the basilar process of the occipital bone and the pterygoid processes. It is very irregular in shape, and consists of two regions, the palato-maxillary proper and the pharyngeal. The principal objects deserving notice are the incisive duct in the palatine vault, for the naso-palatine nerves; the pterygo-palatine canal at its posterior angles, for the pterygo-palatine branches; and the posterior opening of the nasal cavities. The vault is covered by periosteum and mucous membrane, with the uvula or soft palate suspended at its posterior margin; and the space inclosed by the lower jaw contains the tongue, attached to the hyoid bone, sublingual and submaxillary glands, and is completed by membrane, muscles, and integuments. The superior or thoracic extremities consist of the shoulder, the arm, the fore-arm, the wrist, and the hand.

The shoulder consists of two bones—the scapula or shoulder-blade, and the clavicle or collar-bone.

The scapula is a triangular bone occupying the posterior part of the chest, having a dorsal and a costal surface, and a superior, a vertebral, and an axillary margin.

The dorsal or posterior surface (dorsum) is divided by a transverse elevated spine into two parts, the fossa suprascapularis for the suprascapular muscle, and the fossa infrascapularis for the infrascapular muscle. The latter is concave above, convex in the middle, and concave towards the axillary or external margin (costa), from which it is separated by a round line or crest for the attachment of the fascia which separates the infrascapularis from the teres major and minor. Between this crest and the axillary margin above is a convex surface, of a triangular shape, with the apex above, for the attachment of the teres minor, and below a flat quadrilateral surface for the teres major.

The spine is a triangular-shaped eminence, rising obliquely from the upper fourth of the dorsal surface; low at the vertebral, elevated at the axillary margin, where it terminates in a broad, flat surface, also triangular, named the acromion or shoulder-top. In the posterior margin of the spine may generally be distinguished two surfaces separated by a ridge. Above the ridge the cucullaris is fixed; below, part of the deltoid is attached; and between is a common aponeurosis. The ridge is biparted towards the acromion, leaving an interval covered by periosteum and integuments only. The anterior part of the acromion presents a cartilaginous facette, for articulation with the acromial end of the clavicle. To its posterior and external margin the deltoid is attached, and to its tip the acromio-coracoid ligament is fixed.

The costal or anterior surface is of a triangular shape, with the apex below, generally concave, but subdivided into smaller spaces by two or more oblique ridges, to which intermuscular fasciae are attached. This surface, which is the subscapular fossa (venter), lodges the belly of the subscapular muscle, the fasciculi of which are interposed between the aponeurotic ridges. Near the vertebral margin is an irregular surface, to which, and also to the margin, the serratus magnus is attached.

The superior margin (costa superior) is thin and pointed behind, where the levator and omohyoid muscles are attached, and becomes sinuous externally, with a notch converted by a ligament into a hole for the transit of the suprascapular vessels and nerves. The inner or axillary extremity terminates in an elevated hooked process, the coracoid, to the tip of which are fixed the coraco-clavicular ligament, and the united origin of the short head of the biceps flexor and the coraco-brachialis, to the anterior margin the small pectoral, and to the posterior the acromio-coracoid ligament.

The vertebral or posterior margin (costa posterior, basis of some authors) is thin, and ascends straight to the spine, giving attachment to the rhomboideus; then bends forward, and forms with the superior an angle, to which, as also to the edge now mentioned, the levator is fixed.

The axillary margin (costa axillaris, sometimes inferior) is round and broad above, and narrow below. It presents above, first the glenoid cavity, round at its lower margin, angular above, hollow, covered by cartilage and synovial membrane for receiving the head of the humerus. At the angular point above is a surface for the attachment of the long head of the biceps flexor, and the lower margin presents two tubercular eminences for that of the long head of the triceps extensor. Below this are fixed the teres minor, the subscapularis, and the teres major. The latissimus dorsi, passing over its lower angle, binds it down.

The scapula consists chiefly of compact bone, with little cancellated matter interposed. In the subscapular fossa this becomes completely absorbed, rendering the bone thin and translucent, sometimes perforated. The spine, processes, and angles contain cancellated matter. It is formed from one part for the body of the bone, with epiphyses for the coracoid process and the margins. Nutritious holes are generally found in the angle formed by the spine with the body, and in the axillary margin.

The collar bone or clavicle is a cylindrical bone, alternately incurvated like an f, placed at the upper part of the collar bone, chest, between the sternum and acromion of the scapula. It has therefore two extremities, a sternal and acromial, with intermediate body.

The sternal end is triangular, cartilaginous, concave and convex in opposite directions, surrounded by ligamentous insertions. The acromial end is flattened and recurved, presenting a lunated surface for articulation with the acromion.

The body, with the shape of a triangular prism at the sternal end, is rounded above for the attachment of the clavicular portion of the sterno-mastoid muscle, and presents below a rough surface for the costo-clavicular ligament, and a situated line for the subclavian muscle. Towards the acromial end, where it is flattened above and below, it presents before, a surface for the attachment of the large pectoral and deltoid muscles; behind, another for the cucullaris; and below, a prominent oblique crest for the coraco-clavicular ligaments.

Compact in the middle, and cancellated at its extremities, the clavicle is developed from a single point.

The arm-bone or humerus (os brachii) is a long cylindrical bone, divided into head or scapular end, cubital or lower end, and shaft or body.

The head presents three eminences, the articular head, the anterior tuberosity, and the external tuberosity. The first, which is hemispherical, incrustated by cartilage and synovial membrane, with the axis oblique to that of the bone, and articulating with the glenoid cavity of the scapula, is separated from the bone by a narrow depressed line named the neck (collum), in which is fixed the margin of the scapulo-humeral capsular ligament. The second is a small, pointed, sometimes bifid eminence, to which the tendon of the subscapularis is attached. In the external tuberosity are distinguished three facettes, to the upper of which the tendon of the suprascapularis, to the middle that of the infraspinatus, and to the posterior the tendon of the teres minor, are inserted. Between the anterior and the external tuberosity is a longitudinal groove named the bicipital, for the transit of the long head of the biceps flexor.

The cubital or lower extremity is flattened transversely, and moulded into different eminences and depressions. Internally is the inner or ulnar condyle, large and prominent, for the attachment of the internal lateral ligament, and a tendon common to the pronator teres, palmaris longus, flexor sublimis, radialis internus, and ulnaris internus. Externally is the outer or radial condyle, to which are attached the external lateral ligament, and the tendon common to the supinators and extensors, viz. supinator longus and brevis, anconeus, radialis externus, ulnaris externus, and extensor communis. Between these is an articular surface covered by cartilage, moulded into the small head which moves in the cavity of the radius—a groove corresponding to the margin of the latter; the semicircular crest interposed between the radius and ulna. The ulna or cubit (cubitus) is a long bone placed at the inside of the fore-arm, articulated above with the humerus, below with the carpus or wrist, and laterally with the radius. Its superior or humeral extremity consists of two eminences, and an intermediate semilunar or crescentic cavity. The first is a large head named the olecranon (ωλεκρανον, ulnae caput, or elbow; processus anconae, ancon); irregular above, with a small space behind, where the tendon of the triceps extensor is fixed; concave and cartilaginous before, where it forms part of the sigmoid cavity. The second is a broad, thin-edged process, prominent before, about half an inch below the olecranon, the upper surface of which is cartilaginous, and completes the sigmoid cavity; the lower surface is rough for the brachialis internus, some fibres of the pronator teres, the flexor sublimis, and the internal ligament of the humero-cubital articulation. At the outside, and continuous with the sigmoid cavity, is a small semicircular cartilaginous surface—the small semilunar—for articulating with the head of the radius.

The lower or carpal extremity presents a cartilaginous surface, shaped like a circular sector, the circular margin being bent upwards, so as to form a circular surface for the inner articular surface of the radius, while from the centre of its radii arises a pointed process named the styloid, to the tip of which the external ligament of the radio-carpal articulation is fixed. Between the styloid process and sectorial surface is a depression, to which is fixed the fibro-cartilage of the joint; and behind and without the styloid process is a longitudinal groove for the motion of the tendon of the ulnaris externus.

The shaft has the shape of a trilateral prism, except at the lower extremity, where it becomes cylindrical. Of the three lines by which the surfaces are bounded, the external or radial, which is strongly marked, and sharp at the middle, extends from the posterior tip of the small sigmoid cavity to about two inches above the lower end, and gives attachment to the interosseous ligament. The second, internal or ulnar, which is obtuse, descends from the inner edge of the coronoid process to the inside of the styloid, and gives attachment above and in the middle to the flexor profundus, and below to the pronator quadratus. The third, posterior, obtuse above and below, sharp in the middle, extends from the olecranon to the outside of the styloid process, and gives attachment to an aponeurosis.

Of the surfaces inclosed by these lines, to the anterior, which is concave, and contains the medullary hole, the flexor sublimis is attached above, and the pronator quadratus below. The inner is covered above, where it is broad, by the flexor profundus, and below by the integuments. The posterior or radial is parted by a line into two spaces, to the larger of which are fixed the anconeous and ulnaris externus, and to the smaller the supinator brevis, extensores pollicis longus et brevis, the abductor pollicis, and extensor indicis.

The radius is a long bone, rather shorter than the ulna, forming the outer bone of the fore-arm, articulated above with the humerus, below with the carpus, and at the inside with the ulna.

The upper extremity consists of a circular cartilaginous head, concave for receiving the small head of the humerus, with a cartilaginous surface on its inner or ulnar side for articulating with the small sigmoid cavity of the ulna, and a rough one for the annular ligament on the outside. Below this the bone is contracted and forms the neck of the radius, and again swells before into a large rough prominent tubercle, to which the tendon of the biceps flexor is fixed, and which is therefore named the bicipital tuberosity.

The lower extremity, which is double the size, forms an extensive surface for articulation with the scaphoid and lunular bones of the carpus, continuous on the ulnar side with a small cartilaginous surface for articulation with that of the ulna, bounded without by the styloid process, a rough triangular eminence, to which is fixed the external ligament, and bounded elsewhere by a rough margin for ligamentous insertions. The posterior part of this end presents two eminences inclosing a wide hollow, separated by a small eminence into two grooves,—an inner or ulnar; large for the tendons of the extensor communis and the extensor proprius indicis, and an outer or radial for the extensor longus pollicis. Between the middle eminence and the styloid process are two other grooves,—the anterior for the abductor magnus and the extensor brevis of the thumb, and the posterior for those of the radiales externi.

The shaft or body, which is thin and round above, prismatic in the middle and below, presents three surfaces inclosed by an equal number of lines. Of the latter, the inner or ulnar descends from the inner margin of the bicipital tuberosity, sharp and prominent, to the small inner articular surface, and gives attachment to the interosseous ligament. To the outer, which descends from the outer margin of the tuberosity, obtuse, to the base of the styloid process, the flexor sublimis, pronator quadratus, and supinator longus are attached. The third, also obtuse, is indistinct to the second third of the bone, Special whence it proceeds to the middle tubercle of the carpal extremity.

The anterior surface, which is hollow above, presents the medullary hole and the attachment of the flexor longus pollicis below that of the pronator quadratus. The posterior, hollowed in the middle, corresponds to the supinator brevis, the extensors, and abductor pollicis, which are attached to it; and the common extensors, extensor proprius indicis, and extensor pollicis, by which it is simply covered. The external surface, which is rounded, is covered above by the supinator brevis, in the middle by the pronator teres, which are attached to it; and below by the radial extensors (radiales externi), which merely glide over it.

The ulna and radius consist of cancellated structure in the epiphyses, and compact inclosing cancelli in the diaphyses, and are each ossified in three points.

These two bones are mutually connected by a broad web of periosteum continued from that of the bones, and named the interosseous ligament, the principal use of which is to enable the radius to roll laterally in the motions of pronation and supination on the ulna, and to give attachment to muscles without adding to the weight of the fore-arm by intermediate bone.

The bones of the hand consist of those of the carpus, the metacarpus, and the phalanges.

The carpus consists of eight short and irregular-shaped bones, arranged in two rows. Those of the first are the scaphoid or navicular (os sesamoideum, os naviculare), the semilunar (os lunatum), the cuneiform or trilateral (os triquetrum), and the pisiform or lenticular (os orbiculare, os pisiforme). Those of the second row are the trapezium (trapezium), the trapezoidal (os trapezoideum), the large bone (os magnum, os capitatum), and the unciform bone (os unciniforme, os hamatum).

Of these bones, which it would be tedious to describe minutely, it is enough to say, that their names are intended to indicate their shape; that they are connected mutually by cartilaginous surfaces, so as to allow the gliding motion only; and that, besides periosteum, they are invested by ligaments which maintain them in their position, and tend to strengthen and consolidate the wrist, as the basis of support for the hand and fingers.

By the upper articular surface of the scaphoid and semilunar bones, the carpus is connected to the lower extremity of the radius; while the upper surface of the trilateral bone is contiguous to the fibro-cartilage of the radio-carpal articulation, and the upper surface of which is in contact with the lower articular surface of the ulna. The pisiform bone, which is attached to the anterior surface of the latter, and thus projects before the plane of the other bones into the hand, may be regarded as a sesamoid bone, which serves as a point of insertion to the tendons of the flexor carpi ulnaris above, the fibres of the adductor of the little finger below, and those of the anterior carpal ligament before.

The inferior surface of the navicular bone is articulated at once to the superior surfaces of the trapezium and trapezoideum. The palmar or anterior surface of the former presents a small groove, in which moves the tendon of the flexor carpi radialis, bounded on the outside by the pyramidal process, to which the annular ligament is attached. The os magnum, which is articulated above with the semilunar bone, on the radial side with the scaphoid and trapezoidal, below with two metacarpal bones, and on the ulnar side with the unciform bone, is thus wedged firmly like a central base between the others, and contributes much to the solidity of the carpal articulations. The unciform, which is placed at the inside of the range, and is articulated above with the lunar and cuneiform, laterally with the scaphoid, and below with the two inner metacarpal bones, is distinguished by the unciform process rising from its palmar surface, to which part of the adductor and flexor brevis minimi digiti and the annular ligament are attached, and which, stretched between this and the pyramidal process of the trapezium, form a species of arch over the flexor tendons.

The carpal bones consist of cancellated tissue, invested by a thin pellicle of compact bone. In the fetus and infant they are composed chiefly of brown-coloured, callous substance, homogeneous, but without the smallest trace of bone. Their penetration with this substance takes place about eighteen months or two years after birth.

The metacarpus is usually said to consist of five bones. The metacarpal bone of the index finger is articulated above to the trapezoidal and large bone, and on the inside to the metacarpal bone of the middle finger; the latter is articulated above to the large bone, and on the one side to the index metacarpal bone, on the other to that of the ring finger; while the latter and the metacarpal bone of the little finger are articulated above to the unciform bone and to each other.

The bodies of the metacarpal bones are slightly incurved before, and form a hollow which corresponds with the palm. In their intervals are contained the interossei muscles, the internal at the volar, the external at the dorsal surface. The anterior surface is covered by the flexor tendons, the lumbricales, and the palmar fascia. The dorsal surface, which is convex in general, is covered by the extensor tendons.

The index metacarpal bone has attached to its radial margin the first dorsal interosseus, to its ulnar, before, the first palmar interosseus, and behind the second dorsal interosseus; while to its upper anterior extremity the radialis internus is inserted, and to the same extremity behind the extensor radialis longior.

To the second or middle metacarpal bone, besides the palmar fascia and the second and third interossei, the adductor pollicis and flexor brevis are attached to the palmar surface; and the extensor radialis brevis is inserted into its dorsal surface.

The fourth or small metacarpal bone, besides the palmar fascia and the third palmar and fourth dorsal interosseus, gives insertion by its dorsal surface to the extensor carpi ulnaris.

The phalanges or bones of the fingers are fifteen small longitudinal bones placed vertically on each other, three to each finger; or forming ranges distinguished into metacarpal, middle, and ungual, the first row being the longest, the second shorter, and the third or ungual the shortest. The metacarpal phalanges agree in having the upper extremities shaped like rounded cubes, with concave cartilaginous surfaces for receiving the lower extremities of the metacarpal bones, and tubercular sides for the attachment of the lateral ligaments. The upper ends of the middle and ungual phalanges are moulded into two cartilaginous cavities with an intermediate ridge, with lateral tubercles for the lateral ligaments. The lower extremities of the metacarpal and middle phalanges, which are smaller than the upper, are rounded and separated by a small groove into two condyles, which are received into the cavities of the upper ends. The lower extremities of the ungual phalanges, which terminate the fingers, are flattened antero-posteriorly, and moulded into crescentic tips (lunulae) transversely.

The bodies of the metacarpal and middle phalanges are convex behind, and have a surface flat before, bounded on each side by a sharp marginal line, and taper gradually from above downwards. Those of the ungual phalanges, excepting that of the thumb, are convex before as well as behind. The palmar surface of the metacarpal phalanges is covered by the flexor tendons, which in the superficial muscle are inserted into the anterior and upper part of the middle phalanx, while those of the deep-seated flexor are inserted into the upper anterior part of the ungual phalanx. The first phalanx of the thumb, which is generally considered as a metacarpal bone, has the abductor magnus inserted into its upper extremity, and the opponens and flexor brevis into its body. The dorsal surfaces are covered by the extensor tendons, which, with those of the lumbricales and interossei, are inserted into the middle phalanges.

The metacarpal and phalangeal bones are compact, with cancellated extremities, and are ossified in three points.

The bones now enumerated are connected so as to admit of motion to various extents. The humerus, articulated with the glenoid cavity of the scapula by a capsular ligament, while the long head of the biceps serves the purpose of a round ligament, admits of motion in every direction,—flexion, extension, abduction, adduction, circumduction, and rotation. The humero-cubital articulation, which is secured by two lateral ligaments, admits of extension and flexion only; but in any position of the ulna in relation to the humerus, the radius rolls on the former, so as to produce those motions of the wrist and hand which are denominated pronation or internal rotation, and supination or external rotation.

The carpal bones are articulated chiefly with the radius, so as to admit of flexion and extension, adduction and abduction, and even some degree of circumduction and rotation. The metacarpal bones are limited in motion. The metacarpal phalanges admit of flexion and extension, adduction and adduction, circumduction and rotation; while those of the middle and ungual range are confined to flexion and extension. The precision, nevertheless, of which these motions are susceptible, with the numerous modifications which they undergo in combination with the opposable powers of the thumb, and the nicety and delicacy of tact inherent in the skin of the fingers, are the means from which the human hand derives its remarkable aptitude for all the mechanical arts, and all operations requiring manual dexterity. By the combination almost endless of a number of simple motions, so many complex motions are produced, that it is difficult to set limits to the degree of perfection which the hand and fingers, as an organ of prehension, may attain.

§ 7. The Bones of the Pelvic Extremities.

The bones proper to the lower or pelvic extremities are, the thigh-bone (femur), the shin-bone (tibia), and leg-bone (fibula); with the knee-pan (rotula, patella), seven special tarsal bones, four metatarsal bones, and 15 phalanges.

The thigh-bone (femur, os femoris) is the largest, thickest, strongest, and heaviest bone of the skeleton.

The upper or iliac extremity consists of a head, neck, and two tuberosities named trochanters. The head is globular, incrustated by cartilage and synovial membrane, unless at its internal point, where there is an irregular depression for the insertion of the round ligament, and is lodged in the cotyloid cavity (acetabulum). It is situate internally in relation to the shaft; and its axis, which forms with that of the latter an obtuse angle, variable in extent according to age and sex, is represented by that of the neck, a contracted cylinder of bone, varying in length according to the same circumstances, flattened before and behind, presenting numerous vascular holes, and covered by fibrous slips and synovial membrane. The junction of the neck with the bone is marked by a large prominent body named the trochanter major (π), in which four surfaces may be recognised; an external lateral, for the insertion of the gluteus medius, and the motion of the tendon of the gluteus maximus; an internal with a pit, for the insertion of the tendon of the pyriformis, of the gemelli, and of the obturators; an anterior for the insertion of the tendon of the gluteus minimus; and a posterior for that of the quadratus femoris. At the union of the neck with the diaphysis below, and externally, is a conical eminence named the small trochanter (i), to which the united tendon of the psoas magnus and iliacus internus is fixed. The spaces between the trochanters before and behind are united by oblique rough lines, to which the femoral margin of the capsular ligament is attached, and the entire space within which is continuous with the articular cavity.

The lower or tibial extremity, which is large, is moulded into two rounded eminences named condyles (κονδύλαι) (1, 2; a, b); the one internal, deeper, and larger than the external, separated by an antero-posterior depression (fossa intercondylaris), and prominent and convex behind. Each condyle has an external and internal surface, while the articular one, which is incrustated by cartilage and synovial membrane, is shaped something like a horse-shoe, incurvated upwards in the middle before, and behind on each side, with elevated irregular margins for the attachment of the articular capsule. The intercondylar depression before receives the upper part of the knee-pan (patella), while in the intercondylar cavity behind are lodged the fimbriated margins of the synovial membrane, with the femoral ends of the cross ligaments, the anterior of which is inserted into the inner surface of the external condyle, and the posterior into that of the internal condyle. The outer or fibular surface of the external condyle presents an eminence for the attachment of the external lateral ligament, and a depression below for that of the popliteus. The outer or tibial surface of the internal condyle has a prominent tubercle, to which are fixed the internal lateral ligament and the tendon of the adductor magnus. In a pit above each condyle the heads of the gemellus (gastrocnemius externus) are fixed.

The shaft or body, which approaches the cylindrical shape, is incurvated, with the convexity before, and the concavity behind (F, f). The anterior surface is uniformly round, and covered by the crurae, which is fixed above to the interval between the trochanters. The posterior surface presents a rough elevated line, descending from the base of the large trochanter, meeting a similar line descending from the small trochanter, and enclosing a triangular rough space, forming about the middle third of the bone a rough elevated line (linea aspera) (i), which again is parted into two, less distinct; one termi- nating on the external, the other very faint on the inter- nal condyle. To the upper part of the external line, where it is most prominent, the tendon of the gluteus maximus is inserted; next is the short head of the biceps; and to the rest are fixed the fibres of the vastus externus. To the inner line the pectineus and adductor brevis are inserted above, and the vastus internus is attached below; while the adductor longus and magnus are fixed to its whole length, unless at one point, where it is interrupted about three inches above the condyle by a smooth sur- face, on which the femoral artery passes under the tendon of the adductor magnus, to continue its course between the condyles, where it becomes the popliteal artery.

The femur, which is one of the most perfect examples of a long cylindrical bone, is compact in the diaphysis, with distinct medullary canal, and cancellated in the epi- physes. It is ossified in four portions; one for the dia- physis and neck, one for the two condyles, one for the head, and in general one for the trochanter major. The neck, which is short in early life, becomes long in adult age, and the body acquires its peculiar incurvation appa- rently from muscular action. In the female this incurva- tion is greater than in the male, and the neck forms a greater angle with the body.

The knee-pan (rotula, patella) (v) is a short bone, shaped like a heart, with the apex downward, convex and fibrous before, where it is covered by tendinous matter; flat above, where the rectus, the two vasti, and the cruriceps, are inserted; plane and concave behind, where it is covered by cartilage and synovial membrane, and separated into two unequal divisions by a middle ridge, forming the an- terior wall of the knee-joint, and applied by its superior half over the anterior intercondylar fossa. The lower apex is rough for the attachment of the inferior ligament; and to the margins are fixed those of the fibro-tendinous capular, by which it is connected to the femur and tibia.

The knee-pan, which has a peculiar cancellated struc- ture, invested by a thin plate of compact bone, is to be regarded partly as a sesamoid bone for the insertion of the common tendon of the four extensors of the leg, partly as an appendage or epiphysis to the superior part of the tibia, performing to that bone the same function which the olecranon does to the ulna.

The tibia is a prismatic-shaped long bone, situate at the inner and anterior region of the leg, with the femoral condyles above, the astragalus below, and the fibula on the external side.

The head, upper or femoral end, is large, and of an ir- regular oval shape. It presents two slightly concave elliptical cartilaginous surfaces, with the long diameter antero-posterior, separated by a rough vascular space, large before and narrow behind. Of these elliptical sur- faces the external margin is most regular, and presents a crescentic or lunated mark for the attachment of the semi- lunar fibro-cartilages, which thus increase the concavity of the articular surfaces for the reception of the condyles. The inner or mesial margin of each is elevated into a curved peak, mutually separated by a depression. These eminences, which are jointly named the spine of the tibia, correspond in flexion and extension to the intercondylar fossa. Before is a triarcual surface, rough for the insertion of the anterior crucial ligament, and behind a notch for that of the posterior. The lateral circumference of the head, which is rough, and marked by vascular holes, pre- sents before a triangular surface, the upper half of which corresponds to the inner surface of the knee-pan, and is contained within the cavity of the joint; while the lower angular portion is convex for the insertion of the inferior patellar ligament, or the last insertion of the tendon of the rectus and vastus externus. The sides, which are rounded and prominent, are named respectively the external and in- ternal tuberosities, and give attachment to the external and internal lateral ligaments. To the back part of the inter- nal also the tendon of the semimembranosus is fixed (d), while that of the external presents a cartilaginous facette for the articulation of the head of the fibula (c).

The lower or tarsal extremity, which is much smaller, is nearly quadrilateral, with a cartilaginous surface con- cave transversely, with elevated anterior and posterior borders, and the internal raised into a vertical eminence named the inner ankle (malleolus internus) (f), to the apex of which the internal lateral ligament is fixed. This car- tilaginous surface, which receives the head of the astragalus, is surrounded by a furrow, very distinct before, in which ligamentous fibres are inserted; while the external margin, which is broader than the internal, presents between two prominences a trilateral hollow, in which the tarsal end of the fibula is lodged. The anterior surface is covered by the tendons of the tibialis anticus and extensor pro- prius hallucis; and the posterior, behind the internal ankle, is marked by a groove for the tibialis posticus and flexor longus digitorum, and another for the flexor longus hallucis.

The body or diaphysis, which is thick above, is prismat- ic, and presents three surfaces, bounded by the same number of lines. The first, which is anterior (crista), descends sharp and prominent from the anterior margin of the external tuberosity to the fore part of the internal ankle, and, though subcutaneous, gives attachment to the tibial aponeurosis and the tibialis anticus. To the ex- ternal, which is sharp, and descends from the posterior margin of the same tuberosity to the anterior tubercle of the lower end, the intersosseous ligament is fixed. To the internal, which is obtuse, and rather rounded, and descends from the posterior part of the internal tuberosity to that of the inner ankle, the popliteus above, and the second or inner head of the soleus, with the flexor longus digitorum, are attached.

The surfaces bounded by these lines are internal, ex- ternal, and posterior. The first, which is convex, gives insertion above to the sartorius, gracilis, and semitendi- nosus, and is elsewhere covered by integuments only. The external is concave above, where the tibialis anticus is fixed; convex below, where it is covered by the tendons of this muscle, and of the extensor communis and proprius. The posterior is crossed by an oblique line (T, I, Plate XXV.) descending from the fibular articular surface to the internal line, and forming two spaces, the superior of which, triangular, is covered by the popliteus inserted into the oblique line, while the lower, occupied by the tibialis posticus and flexor longus, presents also the medul- lary holes.

The tibia, compact in the diaphysis, with medullary canal, cancellated in the epiphyses, is ossified in three por- tions, one for the former part, and one for each of the latter.

The fibula, which is the most slender bone of the skele- ton of equal length, is situate at the outer side of the bene- tibia, with its lower extremity anterior to the plane of the upper, articulated above with the latter bone only, below with the tibia and astragalus at once.

The head or tibial end, which is of an irregular cuboi- dal shape, presents above an oblique, trilateral, cartilagi- nous surface, articulated with that behind the external tibial tuberosity, by which also it is overhung. Before is a triangular surface, slightly convex, for part of the femo- ro-tibial ligament; behind, a tubercular surface for liga- mentous insertions; and externally, between the two, is an extensive pentagonal surface for the insertion of the The lower or tarsal end consists of a pointed trilateral pyramid, the external surface of which, somewhat convex, is subcutaneous, and forms the external or fibular ankle (malleolus externus) (e). Within is a trapezoidal cartilaginous surface, which is articulated with the astragalus; and behind and below is a rough triangular surface, with a cavity for the insertion of the fibulo-tarsal ligament, while the external ligament is fixed to its angular tip. The posterior surface presents a groove, sometimes two, incrustated by fibro-cartilage for the motion of the peronei longus et brevis.

The body is marked by several lines inclosing surfaces rather irregular in shape and extent. Among the former the following may be recognised:—An anterior, commencing about 2½ inches below the head, distinct in the middle, where the aponeurosis common to the extensor longus digitorum and peroneus tertius before, and the peroneus longus et brevis behind, is attached, and bifurcating about 2½ inches above the lower end into an anterior and posterior, terminating on the anterior and posterior margins respectively of the malleolus externus, inclosing a triangular space, which is covered by integuments only. The internal, descending from about an inch below the head to the anterior edge of the internal malleolus, coincides there with the anterior part of the anterior line. To this, above and in the middle, the tibialis posticus and flexor proprius pollicis, and below the interosseous ligament, are attached. The external or posterior descends from the posterior part of the head, obtuse, and winds round below to the posterior part of the tarsal end, giving attachment to an aponeurosis intermediate between the lateral peronei without, and the flexor proprius and solaeus behind. Between the external and the anterior is an oblique line, to which the interosseous ligament is fixed.

The external surface between the anterior and posterior lines, narrow above, convex and broad in the middle, and winding spirally round the axis of the bone, is covered by the peroneus longus and brevis. An anterior, plane, is covered by the extensor longus and peroneus tertius. The internal or tibial is divided by the oblique line into two; an anterior for the extensor proprius, and a posterior for the tibialis posticus. To the posterior surface above, which is convex, the solaeus is attached; and in the middle and below the flexor longus pollicis; while, by the rough triangular surface below, the bone is articulated with the trilateral cavity of the tibia.

The fibula, which is ossified in three portions, partakes of the general characters of structure common to the long bones.

The tarsus. The tarsus consists of seven short irregular-shaped bones, the astragalus, the heel-bone (calcaneum, os calcis), the scaphoid, cuboid, and three cuneiform bones.

The first (talus, astragalus) has a convex cartilaginous surface above for articulation with the lower end of the tibia, continuous with a similar trilateral concave surface on the inside for articulating with the malleolar process, and with a smaller triarcual surface on the outside for the fibula; two cartilaginous surfaces, separated by a deep pit below, for articulating with the calcaneum; and an anterior eminence, with a convex cartilaginous surface, for articulating with the scaphoid bone before. The calcaneum, which is the largest, consists of the posterior tuberosity (talus) (c), for the insertion of the united tendons of the gastrocnemius and solaeus, and that of the plantaris; two upper cartilaginous surfaces, separated by a ligamentous pit, for articulating with the astragalus; an anterior cartilaginous trilateral surface for the cuboid bone; an internal lateral sinuosity for the passage of the flexor Special tendons, that of the tibialis posticus, and the posterior Anatomy. tibial artery and nerves; and, lastly, an external lateral surface, covered by integuments and the tendons of the lateral peronei.

The scaphoid bone is connected by its posterior concave surface with the anterior convex one of the astragalus, and presents before a cartilaginous surface with three facettes for the three cuneiform bones, and on the outside a small facette for the cuboid. On the inside is a prominent tuberosity for the attachment of the tibialis posticus. The cuboid bone, which constitutes the outer margin of the tarsus, and is articulated with the trilateral surface of the calcaneum, and by a minute facette with the scaphoid bone, is chiefly distinguished by an oblique or diagonal groove, for the tendon of the peroneus longus. The third and fourth metatarsal bones are articulated to its anterior surface.

The three cuneiform bones agree in having posterior cartilaginous surfaces for articulation with the scaphoid bone, and anterior ones for that with the first phalanx of the great toe, and the metatarsal bones of the second and third toes. The internal surface of the large cuneiform bone is convex, covered by integuments; the external or fibular cartilaginous, with two facettes for articulation with the second cuboid bone and the first metatarsal. Its lower surface is irregular for the insertion of the tibialis anticus, and part of the tibialis posticus. The second cuneiform bone, which is the smallest of the three, and the most like its name, is wedged between the scaphoid behind, the first and third on each side, and supports the first metatarsal bone before. The third, which also is not unlike its denomination, is wedged between the scaphoid behind, and the second cuneiform and the cuboid bone, and sustains the second metatarsal bone; while the third and fourth are articulated with the anterior surface of the cuboid.

Of the metatarsal bones there are four; the first three similar to each other; the fourth, which sustains the phalanges of the small toe, distinguished by a large oblique angular head for the insertion of the tendon of the peroneus brevis, while that of the peroneus tertius is fixed above. Of the other three the heads are trilateral or wedge-shaped with the base upwards, with cartilaginous facettes on the sides for mutual articulation. The bodies are cylindrical, and, tapering, terminate in round heads flattened laterally. The dorsal or upper surface is covered by the extensor tendons, the extensor brevis digitorum, and the dorsal vessels and nerves derived from the anterior tibial artery and nerve. The surface of these bones is so constructed that it forms an arched or convex inclined plane, descending from the tibial to the fibular side of the foot. In the anterior or plantar surface, which is concave, are lodged the abductor hallucis, abductor minimi digiti, flexor brevis, the flexor tendons, the accessory flexor, the lumbricales pedis, flexor brevis hallucis, abductor hallucis, flexor brevis minimi digiti, transversalis, and the external and internal ranges of the interossei.

The phalanges of the toes, in number 15, bear a general resemblance to those of the fingers; but are considerably shorter, unless in the instance of the great toe. Like these also, they are disposed in three ranges,—metatarsal, middle, and ungual.

The bones now described are united so as to admit of different degrees and forms of motion. The head of the extremity, lodged in the acetabulum, is retained in that cavity by not only by the capsular and round ligaments, but by the numerous strong muscles with which the hip-joint joint is surrounded. The length of the neck, which is peculiar to the human subject, throws the supporting column of the bone to a greater distance, not only from the pelvis, but from the mesial plane and centre of gravity; and this character, with the great proportional length of the bone, and the extent and direction of the pelvis, constitutes the most decisive argument in favour of the doctrine, that man must support himself in the erect position on the two pelvic extremities. In most quadrupeds the neck of the femur is short; the cylinder is shorter than the tibia, and not arched; and the pelvis, both by its vertical direction and peculiar dimensions, is calculated for the quadruped motion only. The femur admits of motion in every direction,—flexion, extension, adduction, abdication, circumduction, and rotation.

The tibia, with its appendage the knee-pan, is articulated to the condyles of the femur by means of an external and internal lateral ligament, strengthened by an anterior or patellar ligament, posterior fibres, and an anterior and posterior cross ligament, contained within the synovial membrane. The effect of this arrangement, with the anatomical configuration of the articular ends, is to allow cardinal opposition, or flexion and extension only. A small degree of rotation, nevertheless, may be effected.

The fibula is articulated to the tibia above by a genuine capsular joint, and below by fibrous matter, and connected at its internal side by a duplicature of periosteum forming the interosseous ligament. These connections admit of little motion, and the chief use of the fibula is to give attachment to several muscles which bend or evert the foot. The chief weight of the person, divided as it is between each lower extremity, is communicated from the ankle-joint, the pelvis to the femur, thence to the tibia, and finally to the astragalus and calcaneum behind, and the metatarsal bones before. The motion of opposition is confined to the former, which rolls backwards and forwards in the cavity formed by the lower extremity of the tibia and the fibula in the flexion and extension of the foot. In this, therefore, which forms the ankle-joint, all the motions of the foot as a whole are executed. It appears further to be susceptible of a slight degree of lateral rotation, so as to contribute to the eversion and inversion of the foot.

The tarsal bones are mutually connected by cartilaginous surfaces, and secured by numerous fibrous bands, so as to admit of the gliding motion only. This motion is further between each individual articulation very limited, and its general amount is inconsiderable. The great use of the tarsal articulations is evidently stability and solidity as a base of support, not mobility.

The bones of the foot form two distinct and separate arches—an antero-posterior and a transverse. The first is constituted by the posterior part of the heel-bone behind and the metatarsophalangeal articulations before; and its chief use is to distribute the weight of the extremity from the astragalus, which may be regarded as the centre, to the os calcis and extremities of the metatarsal bones on each side. In standing, for example, either on one foot or both, the weight of each extremity is distributed before to the metatarsophalangeal joints, and behind to the tuberosity of the os calcis, while the anterior part of the latter bone and the whole second range of tarsal bones do not touch the ground. The second arch results first from the arrangement of the cuneiform bones with the scaphoid, and that of the cuboid with the os calcis; and next from the arrangement of the metatarsal bones. These arches, which are indistinct in early life, become conspicuous as the bones are completed, and acquire their complete development in adult age. These arches are of great use in the alternate elevation of each half of the person in progression, in ascending an inclined plane or a series of steps, and especially in springing and leaping.

The phalanges are articulated with the metatarsal bones and with each other, so as to admit of flexion and extension chiefly, with a very limited extent of abduction and adduction. The articulation of the great toe, also constitute of the power of opposition, abridges much its extent of motion. While these circumstances, with the great brevity of the phalanges, render the foot much less perfect than the hand as an organ of prehension, they extend its sphere of support, and enlarge its powers as a locomotive agent.

The pelvic and thoracic extremities present several parallel points of resemblance which have been well traced by Soemmering. The head, neck, and tubercles of the thoracolumbar resemble the head, neck, and trochanters of the femur; and if the lower end of the former bone is articulated both with the ulna and radius, while that of the latter is connected to the tibia only, there is still sufficient analogy between the lower ends of both bones. The tibia resembles the ulna above, with the knee-pan corresponding to the olecranon; but the lower extremity of the tibia is represented by that of the radius, in consequence of the extensive connection of the latter bone with the carpus for the purpose of pronation and supination. The navicular and lunar bones of the carpus are represented by the single astragalus,—an arrangement which appears to be allied in the latter case to the purpose of stability and solidity. The calcaneum may be regarded as an enlarged os magnum, fitted for the same purpose; and even in the shape and position of the scaphoid bone the same object may be recognised. This comparison, however, is superfluous to pursue farther. The general conclusion is, that the thoracic extremities are intended to combine with strength great extent and precision of motion, while the purpose of the pelvic is stability, solidity, and strength.

SECT. II.—MYOLOGY; THE ANATOMY OF THE MUSCLES.

The muscles, with their appendages the fasciae, tendons, and synovial sheaths, constitute the second division of the locomotive organs. By the term muscle, indeed, in Special Anatomy, is meant not only a mass of flesh adequate to effect motion, but an organ consisting of fascia, muscular flesh, and tendon, connected by the first and last substances to the parts, fixed or movable, to be approximated. While the middle portion is denominated belly (venter), the two extremities are most properly named attachments; though by others they have been termed respectively head or origin (caput, origo), and insertion (insitus) or termination (finis), according as the one or the other end has been imagined to be most fixed.

By the contraction of the middle portion or belly the two extremities are approximated; and according as the one is connected with a bone or soft part more movable than the other, that movable portion is approximated to the fixed. This, which is the general effect of muscular action, is well exemplified in the primary bones of the extremities, the muscles of which have their fixed end in general in the trunk, and their movable end attached to the bones of the extremities. Thus in the case of the pectoralis major (v), Plate XXVII., and latissimus dorsi (x, i.), Plate XXVIII., the fixed ends are in the trunk, and the movable or insertions are in the humerus; and the effect of the contraction of the belly is to carry the humerus forward over the chest in the one case, and backward on the trunk in the other. This is easily applied to other muscles, as to those of the face.

The converse of this arrangement nevertheless may take place. The extremity, which in ordinary circumstances is the most movable, may be converted into the Special fixed; while that which is fixed becomes movable. Thus, in the case of the two muscles already mentioned, the humerus may become the fixed point; and the effect will be to elevate and approximate the trunk to the part to which the extremity is fixed.

Though all the muscles are agents of motion, all are not of locomotion; and it is chiefly the muscles connected by both ends with the skeleton, and especially those of the extremities, which are entitled to this distinction. The muscles of the face are connected always by one end, often by both, with the skin, and hence are cutaneous muscles. Those of the lower jaw and pharynx are organs of motion simply to move the parts with which they are connected in the acts of mastication and deglutition. Those of the larynx are of two orders, the common or extrinsic, connected to some of the bones of the head and chest; and the proper or intrinsic, pertaining to the laryngeal cartilages only. Those of the eye and ear, external and internal, are equally unconnected with the locomotive faculty.

These circumstances have induced several authors, especially the ancient anatomists, and among the moderns Winslow, to arrange the muscles according to the parts which they move. By others, however, especially Douglas and Albinius, they have been classified according to the regions which they occupy; and this method, which is certainly more strictly anatomical, has been more or less adopted by Innes, Sabatier, Bichat, and Boyer. To the first method the principal objection is, that the same muscle may pertain to different classes of organs, and may effect different purposes in each; while of the second it must be admitted, that it communicates no information regarding the remarkable part which the muscles perform in the complicated processes of the animal machine. This consideration it was which induced Albinius, after a minute description of the situation, connections, and separate actions of each muscle of the human body, to construct a table representing the various classes into which they may be divided, according to the parts on which they act; for the same reason, doubtless, Soemmering arranged them according to the organs to which they belong; and for the same reason Portal, after a description equally minute with that of Albinius, gives a second account of the muscles as they are observed to act in the living body.

In the following tabular view, modified from that given by Albinius in the fourth book of his Historia Muscularum, the muscles are arranged according to their regions.

### Muscles of the Head, Neck, and Vertebral Column.

| Latissimus colli. (II.) | Rectus capitis posterior major. | |-------------------------|--------------------------------| | Sterno-mastoideus. (sr.)| Rectus capitis posterior minor. | | Splenius capitis. (s.) | Obliquus capitis superior. | | Splenius cervicis. | Obliquus capitis inferior. | | Biventer cervicis. | Rectus lateralis. | | Complexus. (c. c.) | Rectus capitis anticus major. | | Trachelo-mastoideus. | Rectus capitis anticus minor. | | Transversus cervicis. | Longissimus dorsi. | | Cervicus descendens. | Scalenes anticus. | | Longissimus dorsi. (l.o.)| Scalenes medius. | | Sacro-lumbalis, and | Intertransversi colli priores. | | Spinalis dorsi. (s.) | Intertransversi colli posteriores. | | Spinalis cervicis. | Intertransversi dorsi. | | Semi-spinalis dorsi. | Intertransversi lumborum. | | Multifidus spinae. | |

### Muscles of the Chest.

| Sterno-costalis. | Levatores costarum brevis. | | Serratus posterior superior. | Intercostales externi. | | Serratus posterior inferior. | Intercostales interni. | | Levatores costarumlongiores. | |

### Muscles of the Abdomen and Loins.

| Obliquus externus. (o.) | Quadratus lumborum. | | Obliquus internus. | Psoas parvus. | | Rectus. (r. r.) | Psoas magnus. | | Pyramidalis. | Iliacus internus. | | Transversus. (t.) | |

### Muscles of the Thoracic Extremities.

#### The Shoulder.

| 1st Order. | Supraspinatus. (s. s.) | | | Infraspinatus. (i. s.) | | 2nd Order. | Teres minor. (t.) | | | Teres major. (r.) | | | Subscapularis. | | 3rd Order. | Latissimus dorsi. (l.) | | | Pectoralis major. (p.) | | | Pectoralis minor. (r.) | | Deltoides. Δ. | |

### Muscles of the Arm.

| Coraco-brachialis. | Triceps brachii. (Tr.) | | Biceps brachii. (n. b.) | Anconeus. | | Brachialis internus. (Br.)| |

### Muscles of the Fore-Arm and Wrist.

| Supinator longus. (s.) | Ulnaris internus. | | Radialis externus longior.| Radialis internus. | | (r.) | Pronator teres. (Pr.) | | | Pronator quadratus. | | | Ulnaris externus. | | | Supinator brevis. |

### Muscles of the Hand and Fingers.

| Extensor communis. | Abductor brevis pollicis. | | Extensor proprius auricularis.| Opponens pollicis. | | Abductor longus pollicis. | Flexor brevis pollicis. | | Extensor minor pollicis. | Adductor pollicis. | | Extensor major pollicis. | Palmaris brevis. | | Indicator. | Abductor digiti minimi. | | Palmaris longus. (p.) | Flexor parvus digiti minimi. | | Sublimis. (r. s.) | Adductor ossis metacarpi digit minimi. | | Profundus. (r.) | Interossei interni. | | Flexor longus pollicis. | Interossei externi. | | Extensor brevis indicis. | Abductor indicis. | | Lumbricales. | |

### Muscles of the Pelvic Extremities.

#### The Hip.

| Gluteus maximus. (g.l.) | Obturator internus. (ob.) | | Gluteus medius. (g. i.) | Obturator externus. | | Gluteus minor. | Quadratus femoris. (q.) | | Pyriformis. | Pectus magnus. | | Gemini. (g. g.) | Iliacus internus. |

### Muscles of the Thigh.

| Biceps cruris. (s.) | Vastus externus. (v.) | | Semitendinosus. (s. r.) | Vastus internus. (v.) | | Semimembranosus. (s. m.) | Cruralis. | | Tensor vaginae femoris. (r.)| Pectineus. | | Sartorius. (s.) | Adductor longus. a. | | Gracilis. (g.) | Adductor brevis. | | Rectus. | Adductor magnus. | Muscles of the Leg and Tarsus.

Peroneus longus. (p.) Its tendon in the groove of the cuboid bone. Peroneus brevis. Extensor l. digitorum pedis. Peroneus tertius. Tibialis anticus. Extensor proprius hallucis.

Muscles of the Foot and Toes.

Extensor brevis digitorum pedis. Flexor brevis digitorum pedis. Abductor hallucis. Flexor brevis hallucis. (r.4.) Adductor hallucis. (u. d.)

Muscles of the Lower Jaw.

Biventer maxillae. Masseter. Temporalis.

Muscles common to the Hyoid Bone, Tongue, and Larynx.

Omohyoideus. Sternohyoideus. Sternothyroideus. Hyothyroideus. Thyroideus. Stylethyroideus.

Muscles of the Palate and Pharynx.

Levator palati. Azygos uvulae. Circumflexus palati. Constrictor isthmi faucium.

Proper Muscles of the Larynx.

Crico-thyroideus. Crico-arytenoideus posticus. Crico-arytenoideus lateralis.

Muscle of the Scalp.

Epicanthus. (e, bz, bz, e.)

Muscles common to the Face and Eye.

Orbicularis palpebrarum. (o.o.) Levator palpebrae superioris. Corrugator supercilii.

Muscles of the Nose.

Compressor narium. (c.) Levator labii superioris alareque nasi. (l.)

Muscles of the Lips.

Levator labii superioris. Depressor labii inferioris. Zygomaticus minor. (z.) Zygomaticus major. (Z.) Levator anguli oris. Depressor anguli oris.

Muscles common to the Ear and Scalp.

Attollens auriculam. Prior auriculae. Retrahens auriculam. Major helicis. Minor helicis. Tragicus. Antitragicus. Transversus auriculae.

Proper Muscles of the Eye.

Attollens. (a.) Plate XXXIII. fig. 6. Depressor. (d.) Abductor. (ab.)

Proper Muscles of the Ear.

Laxator tympani major. Laxator tympani minor. Tensor tympani. Stapedius.

Muscles of the Anus and Perineum.

Transversus perinæi. Transversus perinæi alter. Sphincter ani externus. Sphincter ani internus.

Muscles proper to the Male Generative Organs.

Cremaster. Ischio-cavernosus. Compressor prostate.

Muscles proper to the Female Generative Organs.

Ischio-elitorideus. Constrictor vulvae.

The limits assigned to the present treatise preclude particular details on the situation and relations of this numerous list of muscular organs. Any description sufficiently minute for the purpose of explaining the situation, attachments, relations, and actions of the muscles of the different regions, would be tedious in the extreme, and would not be intelligible without dissection; and no description according to their actions only would be intelligible, without a previous account of their anatomical relations. For these reasons it seems most expedient to direct the attention of the reader to a few general circumstances only. For descriptive details the reader will study with advantage the third book of the elaborate and accurate Historia Musculorum of Albinus, or the more recent treatise of Sandifort. The descriptions of Innes are clear, short, and sufficiently minute; and a good account of the muscles, as they appear on exposition, is given in the London Dissector. Of systematic treatises, the second volumes of those of Soemmerring, Portal, and Bichat are the best.

This section, therefore, we shall conclude with such a general view of the muscles as agents in the attitudes and motions of the trunk and extremities, as, with the occasional remarks on their situation and connections in describing the bones, may be easily intelligible. It is further proper to advert briefly to those of the flexor muscles of the fingers, partly with the view of illustrating the general effects of muscular action, partly to show the mechanism by which the hand and fingers are enabled to execute such a variety of nice and delicate motions.

The muscles of the trunk are employed not only as agents of motion and sustentation, but as the protecting the trunk walls of the large cavities. Thus the external and internal ranges of intercostals, the two pectorals, and the serratus magnus, operate not only in moving the ribs and shoulder respectively, but in contributing to complete the walls of the thorax, and to protect the internal organs. The diaphragm is not only an agent in enlarging the chest downwards, but constitutes an essential partition between the thoracic and abdominal viscera, prevents the lungs and heart from descending into the abdomen, and the stomach and bowels from being thrust upwards into the chest. These characters are still more conspicuously displayed in the recti abdominis, obliqui externi et interni, and trans- versi abdominis, which operate a little in drawing the chest downwards and compressing it before and on the sides, but act much more powerfully as retaining and supporting walls of the abdominal viscera, counteracting by the inward and upward action the downward impulse of the diaphragm. In this manner the abdominal viscera, placed between two opposing but equally balanced powers, are retained in the cavity, and prevented from being protruded upwards or downwards, while they are subjected to the alternate motions of inspiration and expiration.

The muscles of the trunk are employed in retaining that part of the skeleton in the erect attitude; in balancing it properly on the pelvic extremities, in occasionally inflecting and extending it, in bending it to one side, or in producing rotation. Those of the spine and back are particularly the agents of the erect attitude, and of extension; and those of the anterior region are employed in inflecting the person.

Muscles of the thoracic extremities taken together are the agents of numerous varied motions. Though the principal object of the thoracic extremities is prehension, or embracing any object or objects firmly either by one or both hands, this may be modified in various ways, so as to give rise to prehension, traction, and constriction; while diduction and circumduction are the result of the combinations of the simple movements,—abduction, adduction, flexion, and extension.

Prepulsion may be either instantaneous or continued. The first takes place in the act of inflicting a blow or repelling an object. All the flexors are previously put in action to shorten the member, which is then at once forcibly extended, and communicates a violent shock to the part of the object to which its extremity is applied. Of this motion, in which the extension takes place in the scapulo-humeral and humero-cubital articulations, the deltoid and brachialis externus, or third head of the triceps, are the chief agents. The wrist and fingers are almost passive. But an analogous motion is executed by the latter in giving a fillip. In continuous propulsion, for instance, or the act of impelling an object, the mechanism is of two kinds. In the first case, the member being previously extended and supported on the object, the individual inclines the trunk, and avails himself of its weight; while the member, remaining passive, becomes a lever moved by gravity. In the second case, the continued action of the extensors retaining the member forcibly extended, impels the object without interruption. When, for example, a man pushes a wheel-carriage before him, the superior extremities are extended and communicate motion to the carriage, while the trunk approaching it immediately, the extremities are again inflected, and so forth successively. In most instances this twofold mechanism is combined. When in prepulsion the body impelled is fixed, the impulse is thrown back on the person of the prepelling agent. Examples of this effect of prepulsion are observed in the act of rising from a seat by the occasional use of the thoracic extremities, and in pushing a vessel from the shore by means of an oar or pole.

Traction, which consists in a general action of the flexors of the thoracic extremities, is directly the reverse of propulsion. Its effect is to diminish the space between the agent and the object drawn, which takes place by shortening the member; while in propulsion this space is enlarged by elongating or extending the member. In the case of a very great effort, for instance that of detaching a piece of wood strongly fixed in a wall, the action of the flexors is aided by the weight of the trunk, which is instinctively inclined in the opposite direction; and if the body drawn yields at once, a fall is often the result, because in this inclination the centre of gravity is subverted. In another form of traction, in which the body grasped does not yield, and when the action takes place upwards, the effect is to elevate the person of the agent by the flexors of the superior, and even occasionally of the inferior extremities. Familiar examples of this are afforded in the act of climbing walls, trees, and occasionally rocks, in ascending the rigging of a ship, and still more forcibly in the manner in which the active seaman ascends a single rope.

Constriction consists in the forcible and continued in-constriction either of a single hand or of the whole of both members. In the first case the agents are the superficial and deep flexors, and the flexors of the thumb and little finger; and in the second, with the action of these muscles, that of the biceps, brachialis internus, and coraco-brachialis is combined. This motion can neither be so sudden as that of propulsion, nor, like it, can it be aided by the weight of the person.

Diduction, which consists in the forcible separation of Diduction, the upper extremities from each other, as in swimming, is effected partly by the latissimus dorsi and teres major, partly by the posterior fasciculi of the deltoid moving the whole extremity in the scapulo-humeral articulation.

Circumduction, which also is exclusively confined to Circumduction the scapulo-humeral articulation, is effected principally by the deltoid, large pectoral, latissimus dorsi, teres major, &c.; while rotation is performed by the supraspinatus, infraspinatus, teres minor, subscapularis, &c.

Besides these general classes of motion executed by Gesture, the thoracic extremities, to them also belongs the power of assuming many of those attitudes and all the varieties of gesture which man employs for the purpose either of expressing his feelings or giving significance and animation to the language which he adopts for that purpose. How much these gestures, when well chosen and properly introduced, aid both the expression of the countenance and the language of the lips, is well known to the public speaker and the dramatic performer.

Besides the ordinary flexors of the wrist (radialis externus et internus, ulnaris internus), there are two common flexors of the fingers, one superficial (sublimis), the other deep-seated (profundus); the thumb has a long and short flexor, and the little finger has a short flexor. The flexor muscles, therefore, may be distinguished into four orders; those common to the wrist and hand, those common to the hand and fingers, those proper to the fingers, and those proper only to some of the fingers. Though the radialis internus and ulnaris internus chiefly bend the wrist and hand, yet both the superficial and deep flexors, by passing beneath the annular ligament, co-operate in the same motion, and necessarily bend the hand previous to their final action on the digital phalanges. In this they are considerably aided by the action of the palmaris longus and the palmaris brevis, which render the palmar aponeurosis tense, and enable it to afford the necessary resistance to the subjacent flexor tendons.

The superficial flexor, the tendons of which are inserted into the anterior and posterior part of the second row of phalanges, has the effect of bending that part of the fingers; and further, by being bound down by a ligamentous sheath to the first phalanx, inflects them at the same time into the palm. The slits in each tendon allow those of the deep flexor to pass forward on the median line of each phalanx, to be inserted in the ungual phalanges, and thereby to operate most directly and perfectly in inflecting them on the palm; and, by being confined also in the same sheath by strong ligamentous bands, aid in inflecting the second and first range of phalanges. (Plate XXVIII. fig. 2 and 3.) These actions are further facilitated and modified by another class of muscles. The lumbricales, which, situate in the palm, are attached above to the tendons of the flexor profundus, and inserted sometimes into the extensor tendons, sometimes into the lateral regions of the phalanges, may either concur with the profundus in bending the first phalanges, or they may adduct or abduct the fingers, according to the separate or conjunct motion; and hence are of the utmost importance in all nice and minute motions of the fingers. Without the lumbricales, which are peculiar to man, it would be impossible for the human fingers to execute those minute and rapid movements which are necessary in performing on musical instruments; and the great advantage which one individual possesses over another in what is denominated execution, consists chiefly in the perfect use of these little muscles. In playing on the piano-forte especially, the lumbricales are of the most essential service; and though the superficial flexor enables a lady to strike the keys, the former must be employed in the more minute and delicate motions requisite in the transition through numerous chords.

In this action the internodiit at the same time appear to be auxiliary; and their connections are calculated to modify the action of the flexors.

Another peculiarity in the human hand consists in the four muscles with which the thumb is provided, and the two connected with the little finger. By means of its short abductor, short flexor, and adductor, the thumb may be separated, inflected, and approximated to the hand quite independently of the fingers, and with the utmost precision. But from the opposens it derives the remarkable property of being accurately and precisely applied to the tip of any one of the fingers, and thus made to grasp minute objects, which could not without this be effected. From this muscle, in short, the human hand derives its power of appliance to all the arts requiring nice manual operation. Without the opposens there is no penmanship, no painting, no drawing, no tracing, no needlework, no engraving; in short, none of those operations requiring the obedience of the hand to the conceptions of the mind and the guidance of the eye.

The movements of the lower extremities are less distinguished for preciseness and delicacy than those of the superior; and though the foot has both lumbricales and interossei, the brevity of the phalanges compared with the length of the metatarsal bones, and the close connection of the toes, form insurmountable impediments to the rapidity and nicety of motion which is observed in the inflections of the fingers. The circumstance, however, which places the foot at an immeasurable distance behind the hand as an organ of prehension, is the want of the opposens. Void of this, the human foot is little more than the foot of the quadruped, constituting chiefly a base of support, and susceptible of such motions only as are requisite to progression. It is expedient, therefore, to consider shortly the agents by which these functions are performed.

Station, or that attitude in which man supports himself in the erect position on a horizontal plane, is effected by the foot being planted firmly on the ground by means of the gemellus, soleus, tibialis anticus, peronaeus longus et brevis, flexor longus communis digitorum pedis, flexor hallucis proprius, flexor hallucis brevis, flexor brevis digiti minimi et digiti medii, the lumbricales, and interossei. At the same time the leg is fixed to the ground by numerous muscles,—before by the extensors of the great toe and toes generally, by the peronaeus tertius, partly by the tibialis anticus; externally by the peronaei longus et brevis; within by the tibialis anticus and posticus; and behind by the gemellus, soleus, semitendinosus, and long flexors of the toes. The knee is at the same time stretched by the four extensors, aided by the tensor vaginae femoris.

The equilibrium of the trunk and pelvis on the heads of the thigh-bones is maintained by several powerful muscles, connecting the former to the latter. Before, for instance, this action is performed by the sartorius, rectus, the two psoas, and the iliacus internus; behind by the biceps, semitendinosus, and semimembranosus; without by the gluteus and tensor vaginae femoris; and within by the pectineus, the adductors, and the gracilis. By these muscles the pelvis is impelled on the axis of the two femora only, and is prevented from inclining in any other direction. To maintain the trunk above the pelvis in the same steady position, numerous other muscles concur. Behind are the various extensors of the vertebral column and trunk; the longissimus dorsi and sacro-lumbatis on each side, the cervicus descendens, splenius and biventer cervicis; the transversi cervicis, and spinalis cervicis et dorsi; the semispinalis, multifidus, and interspinales on each side. Before are the sternomastoid, the great and small anterior recti, the longi colli, and anterior scaleni; and on each side are the tracheo-mastoid, the lateral scaleni, the intertransversi, and the lateral recti. In this enumeration it is manifest that the muscles of the posterior surface of the trunk and spine are at once more numerous and more powerful than those on the anterior,—an arrangement which is rendered necessary to counteract the effect of the weight of the thoracic and abdominal viscera on the anterior side of the vertebral column, which is thus rendered liable to anterior incurvation, and which becomes so in old age, notwithstanding the agents now mentioned.

This circumstance is further illustrated in the number and size of the muscles by which the head is retained in the erect position, and prevented from inclining forwards. These are the cucullares, the splenii capitis, biventer cervicis, and posterior recti on each side—all powerful, and several of them large.

Station on both pelvic extremities, therefore, requires the co-operation of a very considerable number of powerful muscles; and it is a mistake to imagine, as some authors appear to do, that a small degree of muscular energy is requisite for this purpose, and that the skeleton is the chief means of maintaining the erect position. Without the skeleton, as points of support, the muscles cannot act; but without the muscles the bones are passive brute matter.

In station on one extremity only, a different and certainly a less degree of muscular action is requisite. All one leg, the external muscles of the fixed member are at first strongly contracted, to prevent it from gliding inwards, in which direction the trunk, not supported by the opposite limb, tends to impel it. Proceeding from below upwards, we find the lateral peronei, the vastus externus, and even the rectus, draw the limb outwards; while the tensor vaginae femoris, the gluteus medius and minor, carry the pelvis, and with it the trunk, in the same lateral direction. In this case the weight of the person is employed in antagonizing the muscles of the side thrown into action; and the person is balanced between these two forces.

Elevation on the tip of the foot is effected chiefly by the action of the muscles, which extend the phalanges on the metatarsal bones, viz. the tibialis anticus, extensor hallucis, extensor longus digitorum, and even the extensor brevis; all of which must fix the leg before, and the tarsal and metatarsal part of the foot on its phalangeal region, before the latter can be employed to elevate the person. These extensors, therefore, perform in the tip-toe attitude the duty which the gastrocnemius and soleus execute behind in ordinary station; and the smaller power of the former readily explains the difficulty of maintaining this attitude for a long time.

Progression or gait (incessus) consists in the anterior propulsion of the person by the alternate propulsion of each pelvic extremity. In this, therefore, not only are the muscles necessary to maintain the erect position put in action, but those which bend the lower extremity on the trunk operate on one side, while the extensors of the other maintain that extremity for the instant fixed. Progression consists of a series of steps (passus); and each step consists in the antero-posterior separation of the pelvic extremities by the propulsion of one, while the other remains fixed. Supposing the left foot to be the fixed one, the right foot is elevated, and the leg is propelled by the contraction of the gemellus, soleus, semitendinosus, tibialis anticus et posticus; while at the same time the extensors of the knee raise the leg, and the psoas, iliacus, pectineus, triceps adductor, sartorius and gracilis, with the tensor vaginae femoris, raise and stretch the whole limb. When this is accomplished, the right foot, with the knee extended, the elevating muscles being relaxed, and the trunk, are inclined forwards, and the foot is planted at some distance before the left.

In this motion, however, in which the trunk is carried forward by the recti and obliqui abdominis, and downward by the psoae and iliaci interni, and the leg by the long flexor and the anterior peroneus, a fall would be the immediate result, unless the knee, to preserve equilibrium, were somewhat bent, and the other foot at the same time began to assume the same action. While the toes, therefore, are forcibly impelled by their flexors to the ground, the two gastrocnemii, the anterior and posterior tibiales, and the peronei, elevate the foot with the sole backward, and bend the knee, and the psoas and iliacus raise and extend the whole member.

Running differs from progression, not only in velocity, but in the mode of its accomplishment. Not only are the pelvic extremities more inflected and moved than in mere walking, but they remain inflected. Thus, while the trunk is inclined forward on the pelvic extremities by the recti cruris, the psoae and iliaci, the two latter with the pectineus longus, the adductor longus and brevis, and the tensor, are employed to inflect the thigh, the semitendinosus, semimembranosus, and biceps to inflect the leg, and the anterior tibialis, great and small extensors of the toes, and extensor of the great toe, are employed to bend the foot and the phalanges on the metatarsal bones. The last action is essential to running, which is always most perfect on the tip of the foot. In this movement also the centre of gravity is constantly undergoing change, and is not only carried forward, but makes a sort of undulating motion on each side, and above and below the plane of motion. This is the effect of the pectoral extremities being employed to balance the person.

Leaping. In leaping, the pelvic extremities are much inflected, and the sole of the foot rendered tense, by the gastrocnemius, soleus, tibiales, and peronei, while the extensors are employed to raise the phalangeal part of the foot; when the person is forcibly impelled forward by the gastrocnemius, soleus, the leg suddenly contracting on the cruris in the thigh, and the gluteus, semitendinosus, semimembranosus, and biceps in the pelvis.

Dancing. In dancing, the muscles are made to co-operate in producing a number of complicated motions. In most of the motions composing the dances practised in ordinary society, while the muscles of the pectoral extremities are employed in balancing the person, and those of the trunk in maintaining it in the erect attitude, the flexors and extensors are employed to diduct, inflect, or extend; to cross the extremities with more or less rapidity; and, while the extensors and tibialis anticus elevate the person on tip-toe, the lateral peronei are employed to evert the foot and point the toes.

CHAP. II.—THE ORGANS OF SENSATION.

The organs of sensation may be distinguished into two orders, according as their province is to recognise general or peculiar affections and qualities in external objects. Thus, while it is the purpose of touch to recognise the consistency, shape, and resistance of bodies, it communicates no information regarding their colour, smell, or taste, or the effects which their collision produces in the vibrations of the atmosphere. With these affections of the material world man becomes acquainted by means of organs of a peculiar construction, and adapted to receive the impressions occasioned by these qualities. These organs are, for smell, the nostrils and their appendages; for colour and the general purposes of sight, the eye; for taste, the palate and mouth; and for sound, the ear. For the purposes of common sensation the skin is the agent; but on the structure of this membrane it is unnecessary to add any thing to what has been already said in the General Anatomy, unless that in certain regions, for instance the tips of the fingers, the erectile arrangement of the capillaries, with a minute distribution of nerves, and great thinness of cuticle, communicates the delicacy necessary to the refined purposes of tact.

SECT. I.—THE ORGAN OF SMELL: THE NASAL CAVITIES.

The organ of smell consists of an external part for receiving and transmitting substances capable of producing the sensation of smell; and an internal part, in which this sensation takes place.

The nose (nasus), which constitutes the external part, is a pyramidal eminence, bounded above by the forehead, below by the upper lip, and on the sides by the orbits and cheeks. It has two anterior-inferior oval-shaped lateral openings named the nostrils (nores), separated by a partition. It consists above of the nasal bones and the nasal processes of the superior maxillary bones, covered by periosteum, cellular tissue, part of the compressor narium, and skin. Below, it consists of membranous fibro-cartilages, attached to the nasal bone and superior maxillary above and behind, and supported by a middle cartilage (septum narium), which rests on the fissure of the romer below, and is fixed to the vertical plate of the ethmoid bone above, and to which is attached a slip of fibro-cartilage before, named columna nasi. The lateral fibro-cartilages, which are occasionally named wings (ala nasi, pinnae nasi), covered by cellular tissue, muscles, and skin, liberally supplied by blood-vessels and sebaceous follicles, are moved by the levator, compressor, and two depressors. These parts, with the middle septum and columna, are lined by a form of mucous membrane named the pituitary or Schneiderian.

To what was already said of the nasal cavities under the head of Osteology it is superfluous to add any thing, unless what relates to the lining membrane, the distribution of which is exactly according to the extent of the bony walls of these cavities and their subdivisions.

This membrane consists of two layers; a fibrous, which is Narine the periosteum or perichondrium of the nasal cavities; and membrane a mucous, resembling the other forms of this tissue. It is soft, spongy, red, and more or less vascular, with an attached and a free surface, the latter secreting the thin mucus necessary to preserve the membrane in a proper state for receiving odorous impressions. In this mem- Special brane mucous glands are indistinct; but we recognise minute orifices or pores, which may be the follicular cavities on a small scale, or the orifices into which the mucous fluid is poured after secretion by the arteries.

This mucous membrane is supplied from the internal maxillary artery with blood-vessels, which are at once abundant and superficial. These anastomose with the infra-orbital and ethmoidal branches of the ophthalmic artery and some others of the internal carotid. On these circumstances depends the frequency of hemorrhages from this membrane in early life, while the capillary system is energetically employed in the enlargement of the cranio-facial region; and in advanced life, when venous plethora is most conspicuously evident in the vessels of the head.

The nerves which supply the nasal cavities are the first or olfactory nerves principally, the internal nasal of the ophthalmic, and several branches derived from the sphenopalatine ganglion, the frontal, the great palatine, and the vidian. The distribution of these nerves has been beautifully represented by Scarpa (Annot. Acad.), from whom fig. 1 and 2 of Plate XXXIII. are imitated.

SECT. II.—THE ORGAN OF VISION; THE EYES.

The eyes, placed in the orbits, are distinguished into the globes of the eyes, and their appendages.

The globe or ball of the eye, situate at the base of the orbit, has a spheroidal shape, with the antero-posterior diameter longest, and varying in the adult from 10 to 11 lines. The direction of the eye differs from that of the orbit, the axis of which is oblique and convergent behind, while that of the two eyes is parallel.

The eye-ball (bulbus oculi) consists of several membranes, containing fluid or semifluid substances, denominated humours. The external and strongest is the sclerotic, with the cornea enchased in its anterior aperture; next is the choroid and retina; and the iris, a circular membrane, with an annular aperture, is placed transversely across, dividing the cavity into anterior and posterior chambers. The humours are the vitreous, the crystalline lens, and the aqueous humour.

The sclerotic, sometimes named cornea opaca, in contradistinction to the clear cornea, is shaped like a spherical shell, truncated before, and is estimated to occupy about four fifths of the globe. Its exterior surface is covered by the adipose matter of the orbit behind, and by the tendons of the muscles of the eye and the ophthalmic conjunctiva before. Its inner concave surface is lined by the choroid coat. In its anterior opening, which is about six or seven lines diameter, the cornea is enchased by imbrication of the sclerotic; and in a posterior opening about one and a half line in diameter, the ophthalmic end of the optic nerve is fixed. It is fibrous in structure, becoming translucent when immersed in oil of turpentine. Its vessels are generally colourless, and it appears void of nerves.

The cornea, often named the clear or transparent cornea (cornea lucida), to distinguish it from the opaque cornea or sclerotic, which was supposed by the old anatomists to be of the same nature, is a segment of a smaller sphere than that of the sclerotic, attached to its anterior aperture, and occupying the anterior fifth of the eyeball. Before it is covered by a thin pellicle continued from the conjunctiva, behind by the anterior part of the membrane of the aqueous humour; and its circumference is inseparably enchased within that of the anterior aperture of the sclerotic. The cornea consists of several concentric layers of transparent homogeneous matter, void of vessels or nerves, closely united, but separating and becoming opaque after death.

The choroid coat (tunica choroides) lines the inner surface of the sclerotic, to which it adheres loosely, except at the insertion of the optic nerve, where it has a posterior opening, yet may be easily detached. The margin of its anterior opening, which is large, adheres to the ciliary circle and processes, and appears to be continuous with the iris. The outer surface is covered by a brownish-black viscid matter, which partly adheres to the inner surface of the sclerotic. The inner surface, over which the retina is extended without adhesion, is covered by the same brownish-black matter; but of this the retina receives none, as the sclerotic. The choroid is a thin membrane, of a grayish colour when deprived of its brown pigment, translucent, homogeneous, and, so far as observation goes, void of fibres, but liberally supplied by minute blood-vessels, partly from the long, chiefly from the posterior ciliae, which, dividing on its outer surface into numerous ramifications, mutually approximate, and anastomosing, form a network of quadrilateral and trapezoidal meshes. The tunica Rugulosa is imaginary, unless this arrangement of capillary vessels be such.

From these vessels is derived the brownish-black matter (pigmentum nigrum) with which the retinal surface of the choroid is covered. Its appearance on the convex or gum-sclerotic surface is the effect of cadaveric transudation. The nature of this colouring matter is imperfectly known. When first secreted it is brown, but becomes black successively as it continues. It is not affected by the action of light or calorific, and undergoes no change from the operation of the mineral acids, aqua potassar, ammonia, and alcohol. It appears to consist chiefly of carbonaceous matter. Menghini asserts that he has obtained from it minute particles of iron attracted by the magnet.

The anterior orifice of the choroid is firmly connected to a thick ring of grayish pulpy substance, and forming the point at which the sclerotic and cornea without, and the iris within, are united. This ring, named the ciliary circle (ligamentum ciliaris), is readily detached from the sclerotic. Its structure is unknown.

Posterior to this is a range of prominent minute bodies, Ciliary processes, lying over the crystalline lens, varying in number from seventy to eighty. These are the ciliary processes (processus ciliares). They are trilateral-prismatic in shape, about a line and a half long, more distinct and longer in the human eye than in those of most brute animals. Their intimate structure is not very well known; but they are highly vascular, and their vessels appear to be capable of occasional erection. (Plate XXX. fig. 4.)

Anterior to the ciliary circle is the iris, a circular membrane, placed in the transverse vertical position, with anterior and posterior surfaces, and a circular opening in the centre. The exterior ciliary margin (annulus major) is attached, as already stated, to the ciliary circle. The inner or pupillary (annulus minor) is free, and forms what is named the pupil of the eye. The anterior surface is marked by a variety of colours, blue, gray, or black, brown, or that peculiar brownish-black named hazel, and which are not unfrequently allied with the tints of the skin and hair. The same surface presents radiating lines, which pass from the small to the large circle diverging. Both appearances are produced by vascular arrangement. The posterior surface of the iris, which has been distinguished as a separate membrane under the name of area, is covered by the same dark-coloured matter secreted by the choroid, generally more abundant, and of a deeper tint, than the pigment of that membrane. When this is removed by washing, the observer recognises the radiated streaks impressed by the ciliary processes. (Fig. 4.) The different characters of these two surfaces have introduced some anatomists to distinguish the iris into anterior and posterior membranes. Though it has some thickness, this is perhaps a fanciful refinement. The anterior surface, which is continuous with the membrane of the aqueous humour, is different from the posterior, which is continuous with the ciliary circle and choroid. The structure of the iris is chiefly vascular, and its vessels have an erectile arrangement. The long ciliares, from which these vessels are derived, divide each at the ciliary body into two branches, which divericating at obtuse angles, unite with several of the anterior ciliares, and form with them, beyond the ciliary ligament at the large circumference of the iris, an arterial circle. From this arise smaller branches, which, crossing, unite and form within this a second smaller arterial circle, midway between the ciliary and central margin; and from the concavity of this proceed very minute vessels, which radiate in a flexuous manner, and converge towards the pupil, where, anastomosing most minutely, they form a third circle—the marginal ring of that aperture.

It is chiefly in the middle and inner anastomosing circles that the vessels assume the erectile arrangement; and on this circumstance, and not on that of muscular fibres, so often, so positively, so inconsistently, and so erroneously maintained to exist in the iris, does the mobility of that singular membrane depend. On exposure to direct or bright light, on the application of vinegar, alcohol, or any stimulating substance to the eye, and during the presence of inflammation, the erectile capillaries, distended with blood, are elongated, and necessarily contract the pupillary aperture. In the dark, under the influence of henbane (Hyoscyamus niger), deadly night-shade (Atropa belladonna), and some other narcotics, and when the retina is insensible, these vessels seem to lose their faculty of distension, and, perfectly empty and shrunk, allow the pupillary margin to approach the ciliary.

The retina, which is the third and internal tunic, is of the same shape as the choroid, thin, like cobweb, whitish, translucent, inclining to transparent, and very delicate. Its extreme tenacity and looseness from the choroid causes it to collapse unless inspected under water, when it may be unfolded and expanded for examination. Its outer surface is covered by a very delicate membrane, visible only in a very recent eye, discovered by Mr. Jacob of Dublin. It is almost void of red vessels, unless at the part where the optic nerve enters, where one or two from the central artery may be seen. The others are colourless. The assertion that this membrane is an expansion or production from the optic nerve, seems to be gratuitous; for it bears no resemblance to nervous matter, or to the appearance of the optic nerve. It appears to be simply a peculiarly delicate transparent web, fitted to receive the impressions of luminous rays, and to communicate them to the optic nerve, with which it is continuous.

On this membrane, about two lines on the temporal side of the optic nerve, and in the axis of the ball, is a circular yellow spot (macula lutea), from about a line to a line and a half in diameter, with a minute point or hole in its centre (foramen centrale). At this part the retina is much thinner than at any other; and even in the most recent eyes it presents loose folds, which Bichat regards as cadaveric. The yellow spot and its central hole are seen in none of the mammalia except man and the monkeys.

The vitreous humour, occupying about three posterior fourths of the eye, is spherical and convex behind and on its lateral circumference, but concave before for receiving the posterior part of the crystalline lens. Contiguous only to the retina, it is attached to the coats by the branch sent from the central artery to the lens. It is transparent, and consists of two parts, an investing membrane, the hyaloid (membrana hyaloidea), and inclosed fluid. This membrane is not single, but, sending numerous partitions from its inner surface, forms an assemblage of cells in which the fluid is contained. These facts may be demonstrated by incision, bruising the humour, by congestion, or by boiling it. Before, at the outline of the lens, this membrane divides into two folds, one of which is stretched before the capsule, and the other behind. The trilateral-prismatic space resulting from this separation is completed by the capsule, and forms the circular canal of Petit, which is without fluid, and which is demonstrated by inflation. On the anterior fold the ciliary processes are stretched. The structure of the hyaloid membrane is little known; but it is believed to consist of exhalant arteries and colourless veins.

The hyaloid fluid may be separated from the membrane either by incisions or compressing it between two folds of linen. It then has the appearance of a clear but somewhat viscid fluid, like gum diluted with water. Though rendered slightly turbid by boiling water, acids, and alcohol, it does not coagulate,—a phenomenon which is to be ascribed to the small proportion of albumen which it contains. According to the analysis of Berzelius, 100 parts contain 98·4 of water, 1·6 of albumen, 1·42 of muricates and lactates, and only 1/50th of a part of soda.

The crystalline lens, which is transparent and shaped like an oblate spheroid, is situate in the posterior chamber, and in the anterior depression of the vitreous humour, to which the convexity of its posterior surface corresponds. Before also it is prominent and convex; and it is partially covered by the free extremities of the ciliary processes. It consists of two parts, an inclosing capsule and a lens proper.

The capsule is usually distinguished into anterior and posterior walls, both covered by hyaloid membrane, both transparent, and both firm and resisting. By boiling water, alcohol, or the acids, it is rendered opaque, whitish, and horny; and it becomes yellow by contact with the air.

The lens, which is perfectly transparent, consists of two portions; an exterior, peripheral, thick, soft, adhesive, and easily removed; an interior, central, solid, and consisting of concentric plates. Both are indurated and rendered opaque by boiling water, alcohol, and dilute acids; but the central nucleus is the firmest. When dried in the air it becomes yellowish, but retains its transparency, and may be preserved for years. These phenomena are to be ascribed to the presence of a peculiar form of albumen. According to the analysis of Berzelius, 100 parts of the substance of the lens consist of 58° of water 35·9° of peculiar matter, chiefly albuminous, 2·4° of muricates, lactates, and animal matter soluble in alcohol, 1·3° of animal matter soluble in water, and 2·4° of membrane.

The lens possesses a high refracting power; and its chief use is to concentrate the luminous rays within the eye, so as to represent distinctly the image of visible objects on the retina. Spherical and transparent in early life, it is flattened and acquires a yellowish tint in old age.

Between the capsule and lens is found occasionally a fluid which has been named liquor Morgagni. It appears to be the effect of transudation.

On the structure of the lens, whether organic or not, anatomists vary. Vessels have not been recognised in it; and the most rational view is, that it is the product of an organic action probably in the capsule.

The aqueous humour is contained in the anterior chamber, and in that part of the posterior which surrounds the anterior surface of the lens and vitreous humour. It con- Special anatomy consists of 98-10 parts in the 100 of water, a trace of albumen, and about 2 parts of nitrates and lactates of soda. It is contained in a membrane, which lines the posterior surface of the cornea, and is supposed to cover the anterior surface of the iris. This, however, is questionable. In 1768 a membrane of this kind was described by Demours and Descemet, both of whom claimed the discovery with great eagerness and some animosity. These rival anatomists appear to have forgotten that the aqueous humour may be secreted as well by the cornea and iris as by a proper membrane.

The relation of the coats and humours of the eye to each other may be understood by the diagram (fig. 3, Plate XXX.), where A is the anterior chamber, P the posterior, L the lens, and c, c the ciliary processes. The other parts are easily understood from the foregoing description.

The eye is supplied with blood chiefly by the ophthalmic artery.

The eyeball, thus constituted, is moved in different directions by six muscles, is moistened externally by fluid secreted from a particular gland, and is protected from external bodies by the eyelids and their appendages.

Of the muscles, four are straight and two oblique. The former (attollens, depressor, adductor, abductor), attached to the margin of the optic hole, and terminating in tendons inserted into the superior, inferior, nasal, and temporal parts of the eyeball, raise, depress, adduct and abduct the organ. Of the two latter, the superior oblique (trochilus), which is attached to the margin of the same hole, passes through a pulley-like cartilage at the inner margin of the vault of the orbit, and is inserted into the internal region of the ball, rolls the eye forward and inward, and turns the pupil outwards and downwards; while the inferior oblique, attached to the orbital process of the superior maxillary bone, and inserted between the adductor and the optic nerve, rolls it forwards and turns the pupil upwards. These muscles, which occupy the apex of the orbit, are surrounded by a thick cushion of fat, on which the eyeball rolls in its movements. (Plate XXXIII. fig. 6.)

In the hollow, at the outer temporal region of the orbital vault, is placed the lacrymal gland, a granular grayish body, about the size of a bean, consisting of lobules, with arteries in the intermediate furrows, derived from a branch of the ophthalmic, and accompanying veins. (Plate XXXIII. fig. 5 and 7, G, g.) These constituent lobules have been represented, on the authority of Steno in the ox, and the elder Monro in the human subject, to terminate in 7 or 8 minute excretory ducts, opening on the conjunctiva. In man, however, they were sought in vain by Duverney, Morgagni, Haller, and Zinn; and neither Portal nor Bichat have been able to satisfy themselves of the existence of these ducts. It is nevertheless certain that the lacrymal gland secretes the tears, and that the latter issue from its lobules.

The eyes are covered anteriorly by two musculo-membranous folds named the eyelids (palpebrae), attached to the margins of the orbit, and forming by their free margin the palpebral opening, with commissures at each angle (canthus nasalis, et canthus temporalis).

The upper eyelid, which is large, is bounded above by the eyebrow (supercilium), a cutaneous eminence, arched transversely, covered with hairs, and with the corrugator supercilii attached to its nasal end. Between each eyebrow is a smooth space, named the glabella or mesophryon. Into the upper eyelid the levator (fig. 5, L) is inserted.

Each eyelid consists of skin externally, mucous membrane within (conjunctiva), intermediate cellular tissue, muscle, and a fibrous membrane, attached by one margin to the base of the orbit, and terminating by the other in the tarsal fibro-cartilages. These are crescentic bodies placed in the free margin of the eyelids, and by their firmness and elasticity giving the requisite tension to the eyelids when the orbicular muscle acts, or the levator is relaxed. The cutaneous border of the tarsi is occupied by a range of short, firm hairs, named the eyelashes (cilia). In the mucous borders are the orifices of the tarsal or Meibomian follicles, of the same character as the muciparous follicles generally. These are placed in the substance of the eyelid, beneath the conjunctiva, and behind the tarsal fibro-cartilages. From the inner surface of the eyelids the palpebral conjunctiva is continued over the anterior part of the sclerotic and cornea, forming the ophthalmic conjunctiva.

In the nasal angle is lodged a minute red body, named Caruncle, the caruncle (caruncula lacrymalis), chiefly consisting of filamentous tissue and vessels covered by mucous membrane; and behind this is a fold of the membrane, which has been named membrana nictitans, large in the lower animals, but often so imperfect in man as to be merely rudimentary.

At the nasal end of each eyelid is a minute capillary orifice which leads into a horizontal canal, terminating in orifices, a membranous sac lodged in the depression of the lacrymal bone. These orifices, which are named the puncta lacrymalia (p. p. fig. 5), are the superior or palpebral openings of the lacrymal sac and passages, the lower aperture of which is found in the inferior nasal meatus. The tears effused from the lacrymal gland at the temporal region of the orbit are carried, by the frequent action of the orbicular muscle, over the ball, till they reach the nasal angle, where they are gradually absorbed by the capillary orifices of the puncta, and conveyed into the sac, and eventually to the nose.

The eye derives nerves from six different sources, all of which, however, may be distinguished into three classes, nerves, the sensitive, motile, and trophic nerves. The first consists of the second, optic or the proper visual nerves. The second class comprehends the third, fourth, and sixth nerves, of which the third or oculo-muscular are distributed to the levator palpebrae superioris, the attollens, the adductor, the depressor, and the obliquus inferior; the fourth is entirely distributed to the obliquus superior; while the sixth pair are confined to the abductor. The third class of nerves is derived from the ophthalmic or quadrilateral ganglion, which is formed chiefly from the junction of a sub-branch of the naso-ocular branch of the first or ophthalmic division of the fifth pair, with a small branch of the third nerve. From this arise a small superior cluster of three nerves adhering to the optic, and a large inferior cluster of eight or ten nerves, which quickly join the ciliary arteries, and are with them distributed in the circular ciliary and posterior part of the iris. (Plate XXXIII. fig. 7.) From the other branch of the naso-ocular nerve, the caruncle and lacrymal canal, with the orbicular muscle and epicranium on the one hand, and the lacrymal gland on the other, receive nervous filaments.

Sect. III.—The Organ of Hearing; The Ear.

The organ of hearing consists of the auricle or external ear, with the ear-hole; the middle ear, including the tympanal cavity and its appendages; and the internal ear or labyrinth.

The auricle is a fibro-cartilaginous substance, moulded into a conchoideal shape, covered by skin, attached to the cranium by ligaments, and susceptible of motion by muscles. It is common to distinguish in it the following parts. The helix, a semicircular eminence above the ear-hole; the groove of the helix below it; the antihelix, an eminence commencing in the groove by a superior, broad, Special oblique portion, and an inferior, narrow, horizontal one; the fossa navicularis; the tragus, an anterior eminence below; the antitragus, a smaller eminence behind; the lobule, a pendulous body at the base behind; and, lastly, the concha, a deep conoidal cavity leading to the ear-hole.

The latter is a canal about 10 or 12 lines long in the adult. Twisted at first obliquely forward and upward, it bends slightly backwards and downwards, forming a convexity of incursion above, and a concavity below. Though the extremities are large, the middle is contracted; and it cannot be termed cylindrical, for its section is elliptical or oval. The structure of this tube is fibro-cartilaginous externally where it adheres to the bone, lined by skin passing into mucous membrane, and occupied by minute follicles (glandula ceruminosa), which secrete the wax (cerumen) formed in this canal. The nature of this secretion is imperfectly known. Though, like oil, it stains paper, it is partly soluble in tepid water, and forms with it a yellow emulsion. It is secreted at first fluid, and acquires consistence by exposure to air and admixture with dust. Alcohol has little influence on it. The internal extremity of the auditory canal is bounded by the vertical membrane of the tympanum.

Within this is the tympanal cavity, a space of an irregular cylindrical shape, directed obliquely, nearly in the axis of the pyramidal portion, in the base of which it is contained. This cavity is shut up externally by the vertical tympanal membrane (membrana tympani), and is bounded within by the bony partition which separates it from the labyrinth. The membrana, which is oval-shaped, or nearly round, and attached to the margin of the meatus externus, is directed obliquely downwards and inwards, and is so delicate that it is difficult to determine its structure in the human subject. In the elephant, however, and other large animals, it presents radiating fibres, which are believed to be muscular (Plate XXXVII. fig. 14); and Sir E. Home represents it as such not only in the elephant and whale, but in the human subject. The outer part is evidently a sort of epidermis, continuous with that of the canal; the inner is a mucous epidermis, continuous with that of the tympanal cavity; and between these the muscular fibres are interposed.

The tympanal cavity communicates behind with the mastoid cells, and before and internally by the Eustachian tube, with the pharynx. This tube is estimated to be two inches in length, of which one and a half is in the bone of the pyramid, and about half an inch at its extremity, with the upper side completed by cartilage. Narrow at the tympanal end, it becomes wide and capacious towards the pharyngeal, and presents at length a free open extremity, forming a fissure at the upper and lateral part of the pharynx. The cartilaginous end is covered by mucous membrane continuous with the pharyngeal, and is surrounded by the periostaphylinti, the action of which is believed to separate the walls of the aperture. Within the tube, and towards the tympanal end, this membrane parts with its pharyngeal spongy character, and becomes thin and semitransparent where it lines the bone. The same kind of membrane, partaking of the characters of periosteum and mucous, is continued over the tympanal cavity, and into the mastoid cells.

Above the Eustachian tube is a thin osseous plate, which separates it from a small canal, convex below, concave above, and which, commencing in the fissure between the squamous and pyramidal portions, terminates in the tympanal cavity. In this canal is lodged the internal muscle of the malleus, one of the tympanal bones.

These are four in number, very minute, and denominated, from their mechanical figures, the hammer (malleus), the anvil (incus), the lenticular or round bone (ossiculare), and the stirrup (stapes). Of these the malleus is attached to the vertical membrane by its handle, while its head is articulated with the body of the incus. The latter presents two limbs or branches, to the larger of which the stapes is articulated by the interposition of the lenticular bone; while the base of the former rests on the membrane of the foramen ovale. These articulations are secured by capsules, which allow the bones to move freely on each other; and for this purpose the stapes is provided with one muscle, and the malleus with two, an internal already mentioned, and an external passing from the spinous process of the sphenoid bone to the slender process of the malleus. On the motions of these, however, and their part in the process of hearing, we have only conjectural statements.

The internal bony wall of the tympanal cavity presents Formen two apertures and a convex intermediate eminence. Ofoval, the apertures, the first, which is named the oval or vesti-fenestral aperture (foramen ovale, fenestra ovalis), is situated above, oval transversely, with its great diameter horizontal antero-posterior. It communicates with the vestibule, but is closed by a fine membrane, to which the base of the stapes is fixed, and for the insertion of which its margin is grooved. The oval aperture is bounded above by a round promontory, corresponding within to the Fallopian aqueduct, and below by a large convex eminence named the promontory (promontorium), which indicates the situation of the cavity named the vestibule. Before and above the promontory is the extremity of the thin osseous plate which separates the Eustachian tube from the canal of the internal muscle of the malleus; and behind is an oblique cavity, which is placed between the lower entrance of the mastoid cells and the pyramid. Below the promontory is the round or cochlear aperture (foramen rotundum, fenestra rotunda), trilateral in early life rather than round, and still preserving in the adult the tendency to this shape; smaller than the oval, and directed backwards and outwards. The round aperture is shut by a membrane, the direction of which is oblique to that of the tympanum, and one side of which is towards that cavity, while the other forms part of the cochlea.

At the upper part of the tympanum is a triangular-Mastoid shaped opening, which leads into a rough short canal, cells terminating in the mastoid cells. These are analogous to the cells of the ethmoid, sphenoid, and occipital bones. They are lined by fibro-mucous membrane, and their use is to afford a posterior sonorous apartment for the vibrations produced in the tympanal cavity.

Near this triangular opening is a small bony process named the pyramidal, in which is a canal for the fleshy part of the stapedius, while the tendon issues from its orifice. Near the base of the pyramidal process is the hole by which the nerve of the tympanum (chorda tympani) passes through the glenoid fissure.

The labyrinth consists of the vestibule, three semicircular canals, and the cochlea.

By removing the stapes and stapedial membrane the Vestibule-oval aperture is opened, and communicates with the vestibule. This cavity, which is irregular in shape, about the size of a grain of barley, is bounded without by the tympanum, within by the internal auditory canal, before by the cochlea, behind by the semicircular canals, and above and below by the solid bone of the pyramid. It is lined by a membrane common to the whole labyrinth. Besides the oval aperture by which it is separated from the tympanum, it has, above, the two anterior openings (ampullae) of the superior vertical and horizontal canals; behind, the two openings (ampullae) proper to the posterior vertical and horizontal canals, and the common opening of the two vertical canals; and before and below, the orifice of the external scala cochleae.

There is still another aperture, which leads into a canal discovered by Cotugno, named the aqueduct of the vestibule. This, which, though distinct in some subjects, is almost imperceptible in others, is near the common orifice of the vertical canals; and from it the aqueduct proceeds first upwards, where it is narrow, then backwards and downwards, widening, and terminates in the fissure on the posterior surface of the pyramidal portion.

The semicircular canals, situate behind the vestibule, are three in number, two vertical and one horizontal. Of the former, one is superior, inclosing by its curvature the substance of the pyramid, and forming a convexity in the adult, very distinct in the fetus; while the other, which is posterior but inferior, is placed with its plane corresponding to that of the posterior surface of the pyramid. The third is placed horizontally between the other two, forming a curvature with the convexity towards the base of the pyramid. (Plate XXXIII. fig. 8, 9, and 10.)

Though denominated semicircular, these canals are larger than semicircular, and may be compared to hollow cylinders, incurved so as to form large circular segments. Each canal has an enlarged extremity named ampulla; and as these two vertical canals have one in common, there are five ampullae. They are lined by the common labyrinthine membrane, and contain a pellucid fluid.

The cochlea, which forms the third part of the labyrinth, is a conical canal turned spirally within itself, so that its base is at the lower part of the vestibule, and its apex at the anterior side of the pyramid, with the orifices for the auditory nerve inclosed in the centre of its turns, while the convexity is directed towards the lower margin of the pyramid. The cochlear canal is divided longitudinally by a thin sharp-edged plate, half bony half membranous, into two independent cavities, the superior of which communicates with the vestibule, while the inferior is bounded by the membrane of the round aperture. These cavities are distinguished as the vestibular and tympanal (scala vestibuli and scala tympani) respectively. At the top they terminate in a common cavity named the funnel (infundibulum). Both are lined by a delicate membrane, in which are contained the ramified filaments of the eighth or auditory nerve. (Plate XXXIII. fig. 10.)

In the tympanal scala, near the round hole, is a minute aperture leading to a narrow canal, which gradually enlarges as it ascends, till it terminates by a slit on the posterior surface of the pyramidal portion, as formerly mentioned. This is the aqueduct of the cochlea, first described, like that of the vestibule, by Cotugno.

These different cavities are supplied with blood chiefly from minute branches of the auditory, a vessel generally derived from the basilar trunk or the vertebral arteries. From the meningeal artery also minute branches enter the auditory canal, and anastomose with those of the auditory artery; and the internal carotid sends to the membrane of the tympanal cavity a branch, the capillary ramifications of which anastomose with those derived from the pharyngeal, transmitted by the walls of the Eustachian tube.

The eighth or the proper auditory nerve enters the cochlea by several minute apertures in the internal meatus, and is divided into two fasciculi, of which the posterior and largest is expanded in the form of soft pulpy brush-like filaments, like a hair-pencil, in a pellucid fluid, in the cochlea; while the smallest, which is anterior, is distributed partly to the bottom of the hemispherical cavity of the vestibule, partly to the beginning of the spiral lamina. (Fig. 10.)

The tympanal cavity is chiefly for the purpose of conveying and augmenting the intensity of sonorous vibrations, while the shape of the auricle is supposed to collect them. But of the mechanism of its operation we know nothing satisfactory. The essential part of the organ of hearing is the labyrinth.

SECT. IV.—THE ORGAN OF TASTE.

It is impossible to define the exact limits of the sense of taste. More or less diffused over the cavity of the mouth, it is particularly confined to the tongue and palate. The former, nevertheless, is remarkable for being a muscular organ, which combines with the faculty of taste the power of prehension and transmission of the alimentary articles both during and after mastication, and is further an essential agent in the faculty of articulation. It is requisite, therefore, to give a short account of the mouth, the palate, and the tongue.

a. The mouth is the cavity formed by the lips before, the The pharynx and isthmus faucium behind, the palatine vault above, the intramaxillary membrane and muscles below, and on the sides by the cheeks. Its horizontal direction may be regarded as one among other proofs of the necessity of the erect biped attitude.

The mouth is lined by a mucous membrane, soft, spongy, red, and vascular. It may be traced from the inner or alveolar surface of the lips to the inner surface of the cheeks on each side over the gums, where it is continuous with that of the alveolar folliculi, over the inner surface of each maxillary ramus, and the attached muscles and glands below, until it is identified with that of the tongue, and above over the palatine vault back to the uvula. In these several points, though its organization is the same, its mechanical arrangement varies considerably as the parts are fixed or movable. Thus, on the palatine vault and at the gums it is tense, and adheres pretty firmly to the fibrous layers forming the periosteum of these parts. In the angular space between the lips and gums, however, in that between the inner surface of the alveolar arch, and all over the lower part of the mouth, where it is connected to the inferior surface of the tongue, it is extensive, loose, moves easily over an abundant layer of filamentous tissue, and is generally disposed in irregular folds. Adhering to the internal spine of the lower jaw, a fold or duplicature containing condensed filamentous tissue is reflected, to be attached to the median line of the tongue, and forms the frenum of that organ. In all points it abounds with muciparous follicles. It also presents on each side of the tongue the orifices of the sublingual glands.

The mouth has two outlets, an anterior or facial formed Outlets of by the lips (labia), and a posterior or pharyngeal formed themouth, by the velum palatinum and its appendages.

The lips are musculo-membranous folds, attached all around to the superior and inferior jaw-bones, above and below the alveolar arches, and parted by a transverse opening or fissure into upper and lower, with right and left commissures or angles (carnis). In the Negro race they are particularly bulky and flescid, with their free margins (protabia) much everted; but in the Asiatic-European they are thinner, and more constricted.

Each lip consists externally of skin continuous with that of the face, internally of mucous membrane continuous with that of the mouth, with interposed filamentous tissue and muscles, well supplied by blood-vessels and nerves.

The point of union between the skin and oral mucous membrane is marked by a rounded edge, covered by a thin, vermilion-red, soft and delicate pellicle, extending between Special Anatomy.

Each canthus. This, which is sometimes named the lips proper (labiola), is the probalium. The blood-vessels distributed to this part of the lips have an erectile arrangement. The marginal region of the lips between the skin and mucous membrane is occupied by the orbicular muscle. Above are the labial ends of the common levators (levator labii superioris alaeque nasi), the proper levators (levator labii superioris), the small zygomatics (zygomaticus minor), and the naso-labial (nasalis labii superioris). Below are the two depressors of the lower lip. At the angles are placed the buccinators, the depressors of the angles, the canine muscle (levator anguli oris), and the large zygomatics.

The lips are supplied with blood from the branches of the external carotid. The external maxillary sends a large branch over the angle of the inferior jaw, upwards and forwards to the labial commissures on each side. This vessel, which is generally named the labial, sends off two, a superior and inferior labial, which are subdivided into numerous minute branches, anastomosing freely with each other, and with the submental and inferior dental branches. They open freely into the capillary veins, constituting a species of erectile tissue.

The lips derive their nerves partly from the superior maxillary, partly from the anterior or mental division of the inferior maxillary, with anastomotic communications from the 8th or facial nerve.

Soft palate.

b. The posterior or pharyngeal outlet of the mouth (isthmus faucium) is formed by the movable or soft palate (velum palatinum), a membranous fold attached to the posterior margin of the palatine quadrilateral bones, and hanging with its free margin downwards. This curtain, which has two surfaces, an anterior or oral and a posterior or pharyngeal, is shaped like a double arch, meeting on the mesial plane, where it terminates in an elongated conical prominence, supposed to resemble a grape suspended by its stalk, and denominated therefore uvula (στραγγός), but which, with the lateral arches, bears a closer resemblance to the descending cusp of a Gothic window. From this central process the arch rises on each side; and when it passes to the outer edge of the palate-bone on each side, it is supported by two musculo-membranous vertical columns, united at the top, but separating and forming an intermediate cavity, in which the tonsil on each side (amygdala) is contained.

The palatine curtain consists of two folds of mucous membrane, with interposed filamentous tissue and muscular fibres. The anterior mucous membrane is of the same character with that of the mouth, with which it is continuous. The posterior, which is continuous with the nasal mucous membrane, partakes of the characters of that tissue, and is redder and more vascular. These two meet in the lower margin of the velum, and pass into each other. Both are well supplied with mucous follicles, but the anterior or oral division most copiously.

These mucous membranes rest on filamentous tissue; and beneath this we find, in the middle, the levator or azygos uvulae, and on the sides the levator of the soft palate (peristaphylinus internus), which are expanded in the velum. The anterior pillar consists of mucous membrane enveloping the fibres of the constrictor isthmi faucium; the posterior incloses those of the pharyngo-staphylinus; and both expanding into the velum, augment its thickness and regulate its motions.

Between the internal peristaphylini, which are immediately below the pituitary or posterior mucous membrane of the velum and the anterior, is an aponeurotic web, connected with the circumflexi, which, fixed to the margin of the palatine vault, tends to consolidate the velum.

The free margin of the velum forms the upper boundary of the posterior or pharyngeal opening of the mouth, while the upper surface of the base of the tongue forms the lower boundary. The size of this opening, which is usually named the isthmus of the throat (isthmus faucium), varies according to the state of the velum and its uvula. In the act of deglutition the velum and uvula are raised by the peristaphylinus internus and azygos uvulae, and the whole curtain is constricted by the constrictor isthmi faucium and pharyngo-staphylinus. In the act of vomiting it is forcibly drawn up against the posterior nasal openings by these muscles; but notwithstanding this, matters from the stomach are occasionally projected through the nostrils. In singing on false notes the uvula is progressively elevated, as the voice ascends.

In the space between the anterior and posterior pillars are contained the tonsils (tonsilla, amygdala), bounded above by the commissure of the pillars; below by the lateral part of the base of the tongue, where they are continuous with the muciparous glands of that organ; before by part of the constrictor isthmi faucium; and behind by the pharyngo-staphylinus. The shape varies in different individuals, though their pendulous attachment gives them the oblong spheroidal or almond-like shape. They consist of several lobules, grayish, soft, and of structure similar to that of the muciparous glands of the tongue. The lobules present minute cavities, isolated or mutually communicating, in the recess of which are minute pores, the orifices of the excretory ducts, and from which a watery but viscid liquor may be expressed. In short, each tonsil may be regarded as an assemblage of muciparous glands, destined to secrete fluid for lubricating the throat during the process of deglutition, when it is most abundant.

The chops (buccae) or lateral walls of the mouth consist externally of skin, internally of mucous membrane and of an intermediate layer of muscles imbedded in abundant filamentous and adipose tissue.

The cutaneous covering is in general thin, soft, and peculiarly smooth, with a minutely distributed and abundant capillary system, which approaches in its characters to the erectile.

Beneath the cutaneous covering is the zygomaticus major, the only muscle proper to the cheek, resting on a thick layer of fat; below this is the buccinator, perforated by the parotid duct; and to the filamentous tissue inside, the buccal mucous membrane, furnished with numerous muciparous follicles, adheres. The orifice of the parotid duct is seen opposite the second molar tooth of the superior jaw.

c. The tongue is a longitudinal muscular organ, invested by a mucous membrane provided with numerous papillae, attached behind to the hyoid bone, below to the mucous membrane of the mouth, and free above and before. It is shaped like a flattened cone, and is distinguished into a base and tip (apex), an upper and a lower surface, and two sides.

The base is somewhat thick and broad, but becomes thin and narrow near the hyoid bone. From about 1 inch anterior to this, however, to near 1½ from the tip, the thickness and breadth are nearly uniform. The tip (apex) is flat and rounded or paraboloid in ordinary circumstances, but may be made by muscular action to taper to an angular point. The upper surface, which is free, presents the lingual mucous membrane divided into right and left halves by a superficial furrow. On this, near its posterior end, is a depression, variable in size, named the foramen caecum, in which are contained the orifices of muciparous follicles. From this on each side proceeds an oblique line diverging forward, and forming with that of the opposite side an acute angle, with the angular point behind. These an- gular lines, which are variable in shape and disposition, depend on the elevation resulting from the mucous glands at the base of the organ. The rest of the surface presents the minute conical eminences named papillae, which belong to the mucous membrane. The lateral margins, which are smooth and void of papillae, form the transition from the upper free papillated surface to the lower, which is chiefly attached by folds of the oral membrane to the lower region of the mouth.

The tongue consists of various muscles, connected by filamentous tissue, some adipose tissue, and invested by mucous membrane.

Muscles.

The muscles are of two orders, those common to the tongue and contiguous parts, and those proper to the tongue. The common or extrinsic muscles are, the styloglossi, between the styloid process and margins of the tongue; the hyoglossi, between the branches of the hyoid bone and the margins of the tongue; and the genioglossi, from the upper internal mental tuberosities to the lower part of the organ. The proper or intrinsic muscle (lingualis) consists of two parallel layers of muscular fibres running along the lower surface of the organ, and a mass of fleshy fibres irregularly arranged and mutually crossing in all directions, and intermixed with a considerable quantity of soft but elastic oleo-adipose matter.

Of the lingual mucous membrane the most important circumstances are, the leathery thickness and distinctness of its corion and epidermis on the superior surface of the organ, and the papillary eminences with which it is marked.

These papillae may be distinguished into three orders; the irregular or granular at the base, the tubercular or rounded about the middle third, and the conical or pointed at the apex.

The granular papillae, which vary in number from 10 to 15 or 16, are of a spheroidal or ovoidal shape, and are arranged on each side of the median furrow, obliquely behind the sides of the angle already mentioned. These bodies are evidently muciparous follicles; and it is in general easy to distinguish the orifice of the excretory duct by the eye or a moderate lens. They seem to receive filaments from the glosso-pharyngeal nerves, which enter the tongue immediately beneath these granular glands.

The tubercular papillae, which are much more numerous, have rounded truncated summits, and occasionally pedunculated stalks. They are irregularly distributed towards the middle, margins, and apex of the tongue, promiscuously with the conical; and their nature is unknown.

The conical or acuminated papillae, though occupying the two anterior thirds of the lingual surface, are nevertheless most numerous towards its apex, where they are also smallest, and somewhat inclined forward. These papillae are asserted by the older anatomists to be the terminations of nervous twigs; and Cloquet allows them to be the expansion of the filaments of the lingual nerve. This, however, is an evident relic of the fanciful representations of the older anatomists, and is not supported by inspection. I have examined the structure of the lingual papillae in many instances, and in none have I seen any ground for the assertion that they consist of nervous filaments. They do not even receive a larger proportion than other parts of the lingual membrane. The papillae consist chiefly of numerous minute blood-vessels, rather tortuous, and communicating directly with veins enveloped in fine filamentous tissue; and from this they derive their property of erection, while their mucous surface secretes mucus copiously. These papillae are further the seat of the white fur with which the tongue is liable to be coated in affections of the stomach. The yellow fur seems to be produced from the mucous surface generally.

The tongue is supplied with blood by the lingual arteries, branches of the external carotid, and by the palatine and tonsillary of the external maxillary. The blood is returned by the superficial vein, the ranine, the lingual, and submental.

The nerves of the tongue are derived from three different sources; the inferior maxillary, or third branch of the fifth pair; the glosso-pharyngeal; and the hypoglossal. From the first it receives the lingual nerve, which, after sending filaments to the sublingual gland, the styloglossus, genioglossus, and proper muscle of the tongue, is distributed chiefly to the upper surface, sides, and apex of the organ. This is believed to be the proper gustatory nerve. From the second it receives a lingual branch, which, passing between the styloglossus and hyoglossus, gives filaments to these, the proper muscle, and the posterior part of the genioglossus, and to the granular papillae. By means of this nerve the motions of the tongue and pharynx are made to associate. The third, which is distributed chiefly to the muscles attached to the hyoid bone, sends filaments also to the hyoglossus, styloglossus, and chiefly to the genioglossus. The hypoglossal is believed chiefly to preside over the motions of the tongue, and probably those destined for articulation.

The tongue is one of the best examples in the human body, of the felicity with which a single organ may be adapted to a great variety of useful purposes. Endowed with the common sensation of tact, diffused over the body at large, its mucous investment is so organized that it recognises readily the peculiar impressions communicated by rapid bodies. To render it more serviceable in this respect, its muscles make it an organ of prehension, and elongate, contract, inflect, incurvate, or extend it, so as to apply objects placed on its tip to the palate or any part of the mouth. By the same means it becomes an important agent in the prehension of food, and in deglutition, by transmitting the masticated food to the pharynx. Lastly, it is a most essential and necessary organ of speech, and, by the nice motions which it undergoes, enables the human race to pronounce literal sounds and articulate consonants, which without its aid would be unutterable. Of this the letters l and r are examples.

d. Connected with the organs of taste are the salivary glands, of which there are three pairs, one on each side of the mesial plane; the parotid, submaxillary, and sublingual.

The parotid, so named from its situation before the ear, Parotid is the largest of all the salivary glands. It consists of two parts, the parotid proper, a large oblong mass placed in the deep angular cavity formed by the maxillary ramus and the mastoid process; and the socia parotidis, a large flat irregularly oval mass extending beneath the skin of the face. Partaking of the general characters of glandular structure, it is supplied with blood from the external carotid, by the temporal and transverse facial; its veins open into the external jugular; and it receives numerous nervous filaments from the facial and the ascending branches of the cervical plexus.

It has an excretory duct, named also the duct of Steno (ductus Stemonianus), which, quitting the surface of the gland a little above the middle of the upper margin of the masseter, proceeds horizontally over the tendinous part of that muscle, and, sinking into the filamentous adipose tissue of the cheek, perforates the buccinator, and terminates in the mouth at the level of the second superior molar tooth.

The submaxillary or intramaxillary is smaller than the Sub-max-parotid. Oblong in shape, it is placed on the internal pitillary. Special of the lower jaw, bounded by the internal pterygoid and mylo-hyoid above, the lingual nerve, the stylo-glossus and hyo-glossus, and the external maxillary artery behind, and below by the latissimus colli and integuments. Blood it derives from the lingual and external maxillary arteries, and nerves from the lingual and the myloid branch of the inferior dental. Its excretory duct, named, from its discoverer, the duct of Wharton, terminates on the side of the frenum, in a narrow tuberculated orifice.

The sublingual gland is the smallest of the three. Parallel to that of the opposite side, it is separated from it by the base of the two genio-glossi, and rests on the mylo-hyoideus, which separates it from the intramaxillary. Occasionally, however, these two glands communicate by a slip from the intramaxillary below the muscle. It is supplied with blood by the sublingual, ramine, and submental arteries; and its nerves proceed from the lingual and hypoglossal. Its excretory ducts are manifold, and terminate either in several orifices on the sides of the frenum, or unite in a single tube, opening in the same region.

The use of these glands is to separate from the blood a watery but somewhat saline and sapid fluid, which has the twofold office of preserving the gustatory membrane in its necessary moisture, and of mixing with the food during mastication.

The saliva consists chiefly of water, holding in solution hydrochlorate of soda, sulpho-cyanic acid, and a minute portion of animal matter intermediate between albumen and osmazone. The presence of sulpho-cyanic acid, an active poison, is remarkable; nor is the purpose of such an agent known. From the saline matters in this fluid the tartar of the teeth is deposited; and occasionally minute concretions are formed in the glands or their ducts. That appearing in the ducts of the sublingual forms one variety of the affection named ranula.

CHAP. III.—THE ORGANS OF VOICE.

Voice is of two kinds, according as it consists in the mere voluntary utterance of sound, or what is named, in reference to the animal world, cry, or in the utterance of certain peculiar modifications of this, denominated therefore articulate voice, or simply speech. Inarticulate voice is common to all the Mammalia and Birds. By the possession of articulate speech, however, man (μέγας) is particularly distinguished from the animal world in general.

These two forms of voice have two distinct organs. For inarticulate voice the larynx is placed at the superior extremity of the windpipe; and for that of speech, to the larynx are superadded the articulating powers of the teeth, lips, and tongue.

The larynx is a tubular organ, consisting of cartilages invested by membranes, connected by ligaments, and moved by muscles.

The cartilages are five in number, the thyroid, cricoid, two arytenoid, and the epiglottis.

The thyroid cartilage, which forms the anterior and lateral region, consists of two lateral halves united on the mesial plane, where they form an acute salient angle, distinct beneath the integuments, and forming what is named the pomum Adamii. The anterior surface is slightly concave, covered by the thyro-hyoideus, with an oblique line, to which the muscle now mentioned, the sterno-thyroideus, and inferior constrictor, are attached, and a posterior space covered by the two latter muscles. The posterior surface of the thyroid has in the middle a re-entrant angle, to which are attached the ligaments of the glottis and the thyro-arytenoi-dei; on the sides two plane surfaces, corresponding above to the cellular tissue of the thyro-arytenoi-dei, and below to the lateral crico-arytenoi-dei, and some fibres of the Special crico-thyroidei attached to this part.

Each lateral half is quadrilateral and quadrangular. To the upper margin, which is obliquely situated like an s, the thyro-hyoid membrane is attached. To the lower, which though shorter is also sinuated, the crico-thyroid membrane and the crico-thyroidei are attached.

The posterior margins, which are oblique and give attachment to several fibres of the stylo-pharyngei and palato-pharyngei, terminate above in an elevated pointed process incurvated inwards and forwards, connected by a ligament to the hyoid bone, and below in a similar process, shorter however and triangular in shape, and articulated by its tip with the lateral process of the cricoid cartilage.

The cricoid or annular cartilage (xiphos, annulus), which Cricoid occupies the lower part of the larynx, is a complete ring cartilage of cartilage, narrow before, and broad and elevated behind, where chiefly it constitutes the laryngeal cavity. Convex in the middle, where it is subcutaneous, it widens laterally where the crico-arytenoi-dei are attached; and farther back, where it is covered by the thyroid cartilage, it presents the lateral process covered by synovial membrane for articulation with the triangular process of the thyroid. Its posterior region is broad and quadrilateral, with a ridge on the median line covered by the pharyngeal membrane only, and two depressions on each side, to which the posterior crico-arytenoi-dei are attached. The inner surface, which is concave, narrow before and broad behind, is covered by the laryngeal mucous membrane.

The superior margin presents before a large notch, to which the crico-thyroid membrane is fixed, laterally the insertion of the lateral crico-arytenoi-dei, and behind two convex surfaces, oblique in direction, covered by synovial membrane for articulation with the arytenoid cartilages, and between which this margin is covered by the arytenoid muscle. The lower margin, less irregular, descending before, sinuated on the sides and notched behind, is united by a fibro-mucous membrane to the first ring of the windpipe.

The arytenoid cartilages are two small bodies, triangular-arytenoid lar and pyramidal in shape, placed at the posterior part cartilages of the larynx, in the upper margin of the cricoid cartilage. In each arytenoid cartilage may be recognised a concave anterior surface for the arytenoid gland, a concave posterior surface for the arytenoid muscle, an internal surface covered by laryngeal mucous membrane, a base concave and oval, covered by synovial membrane for articulation with the cri- coid, and a thin, convex summit, supporting a small cartilage (cornicula laryngis), invested by mucous membrane.

These bodies, which are named the tubercles of Santorini (capitula arytenoidea) by whom they were discovered, are conical in shape, with a concave base for articulation with the summit of each arytenoid cartilage, and a pointed apex incurvated inwards and backwards. To their surface, with part of the arytenoid, the thyro-arytenoid ligament is fixed, and forms the beginning of the glottis.

These bodies partake of the general characters of cartilage, and are invested by perichondrium. The thyroid and cricoid have a great tendency to ossification; and it is rare to find them unossified in advanced life.

The epiglottis is a thin slip of fibro-cartilage, of a para-epiglottoid shape, covered by mucous membrane, attached at its base by cellular tissue to the inner surface of the hyoid bone and the upper margin of the thyroid cartilage, and by duplicatures of mucous membrane to the summits of the arytenoid cartilages. In this duplicature, the cuneiform cartilage, with the base upward, named the cuneiform laces.

These cartilages are articulated so as to admit of mo- The articulations are secured by ligamentous capsules; but the most important ligament is the thyro-arytenoid, which passes from the base of each arytenoid cartilage to the re-entrant angle of the thyroid, where the fibres are mutually mixed with that of the opposite side. The thyroid moves on the cricoid, which may be regarded as the base of the organ; and the two arytenoid move on the upper margin of the cricoid. The epiglottis is depressed over the laryngeal opening by the motion of the tongue in deglutition.

The agents of motion in the larynx are of two kinds: 1st, those which move the whole organ in relation to the neighbouring parts; and, 2ndly, those which move the component parts of the larynx in relation to each other. To the former class belong the sterno-thyroid, thyro-hyoid, and inferior constrictor muscles, with those attached to the hyoid bone, the elevation and depression of which the larynx follows. The second comprehends the crico-thyroid, the posterior crico-arytenoid, the lateral crico-arytenoid, the thyro-arytenoid, and the arytenoid. The connections and relations of these muscles it is superfluous to detail more minutely than may be understood from the description already given of the cartilages. It is sufficient to say, that while the crico-thyroid causes the thyroid cartilage to perform a swinging motion on the cricoid, the posterior crico-arytenoid draws the arytenoid cartilages back, the thyro-arytenoid draws them forwards, the lateral crico-arytenoid separates them from each other, and the arytenoid, sometimes distinguished into transverse and oblique arytenoid muscles, approximates these cartilages in different degrees, according to the act in which they are used.

The several parts now mentioned are invested on the inside by mucous membrane, continuous above with that of the pharynx and tongue, and below with that of the trachea. Proceeding from the former boundary, it may be traced over the epiglottis and its gland, on the medial plane and the thyro-arytenoidei, and on the sides from the inner surface of the thyroid cartilage before to the outer margin and base of the arytenoid cartilages behind. At this part it rises to form two folds with rounded margins, extending from before backwards, and forming on the outsides a cavity with the arytenoid cartilage. These folds, though occasionally named the superior ligaments of the glottis, are truly mucous membrane doubled, with interposed filamentous tissue. They form an intermediate triangular space, with the base before and the apex behind. The inner surface of this membrane, directed to that of the opposite side, is concave, and forms a sort of pouch called the ventricles of the larynx (sacculi laryngis). The membrane here covers the thyro-arytenoid ligaments, over which it is tensely stretched, so as to form inferior folds, much tenser and firmer than the superior ones. These lower folds, which form a triangular interval with the base behind and the apex before, are the proper ligaments of the larynx, or vocal chords (chordae vocales); and the intermediate fissure is named the glottis, or rima glottidis. Though this opening is triangular in the dead body, its shape varies much in the living. By the joint action of the posterior crico-arytenoidei and the arytenoidei transversi, the thyro-arytenoid ligaments may be rendered tense, the arytenoid cartilages approximated, and the fissure of the glottis become a mere slit.

Though it is impossible to adopt all the views of Daudart regarding the powers of the thyro-arytenoid ligaments, it is certain that their tension and relaxation, with the mutual approximation of the arytenoid cartilages, are the essential agents of voice. Without the air passing through the glottis there is no voice. The glottis is also the organ by which the quantity of air admitted into the trachea is regulated. By means of its muscles it may be shut, and the breath retained, so as to fix the chest during any great effort. By contracting it, also, during coughing or forcible expiration, the air is forcibly expelled from the lungs, and necessarily carries at the same time foreign bodies.

At the base of the epiglottis, in the angle between it and the thyroid, the laryngeal membrane presents several orifices, which may be traced to a cluster of follicles imbedded in the submucous tissue at this part. This cluster has been named the epiglottic gland.

A similar glandular body, in the anterior depression of each arytenoid cartilage, is named the arytenoid glands.

Of the body named thyroid gland, situate on the sides of the upper end of the trachea, and generally referred to the appendages of the larynx, nothing is known. With the larynx it has certainly no relation.

The blood-vessels of the larynx are the superior thyroid or laryngeal, the first branch of the external carotid, and the inferior laryngeal branch of the inferior thyroid, the second branch of the subclavian artery.

The nerves are derived from the pneumogastric or nervus vagus, and may be referred to three divisions; the internal laryngeal, distributed to the proper muscles of the larynx; the external laryngeal, distributed to the thyro-pharyngeus, the sterno-thyroid, hyothyroid, and crico-thyroid; and the recurrent, distributed to the laryngeal membrane, the thyro-arytenoid, and posterior crico-thyroid muscles. The division of these nerves, or of the pneumogastric, from which they proceed, is followed by palsy of the muscles, and inability to open the glottis at will, or retain it open; and the result is dyspnoea, terminating in asphyxia.

CHAP. IV.—THE NERVOUS SYSTEM.

The nervous system includes two general divisions, a central and a distributed. The first is collected in a single and indivisible mass, contained in the cavities of the cranium and vertebral column, and may be designated by the general appellation of brain (cerebrum). The second consists of long chords connected with some part of the central portion and with each other, and distributed in every direction through the body in the mode of ramification. These are distinguished by the name of nervous chords or nerves (nervi).

SECT. I.—THE BRAIN AND ITS MEMBRANES.

§ 1. THE BRAIN. Plate XXX.

The brain may be considered as a continuous organ, consisting of three divisions—the convoluted, the laminated, and the smooth or funicular portions. Of these divisions, which are framed according to the peculiar external configuration of each, the first part corresponds to what is called the brain proper (cerebrum); the second to the small brain (cerebellum); and the third to the oblong body contained in the vertebral column, and known under the name of spinal chord.

The convoluted portion presents two surfaces, an outer or convoluted, and an inner or figurate. The laminated portion in like manner presents two surfaces, an outer or laminated, and an inner or central. The third has only one exterior surface.

The shape of the first two divisions is like that of the cranial cavity in which they are contained, oblong spheroidal or ovoidal, with the small extremity of the ovoid before, and the large one behind.

The human brain is larger and heavier in proportion than that of any other animal. The three parts, the brain, cerebellum, and spinal chord, after being washed and Special emptied of blood, weigh in the adult from two pounds five ounces to three pounds three ounces, and at an average about three pounds; and of this the brain alone weighs two pounds. The statement of Haller, that the brain weighs five pounds, is incredible, unless it be understood of Troy weight, in which case even it seems exaggerated, since of more than 200 brains weighed by Soemmering, not one amounted to four pounds. The statement, that the brain of Cromwell weighed six pounds and one fourth, seems equally incredible. The specific gravity of the adult brain is to water as 1031 to 1000. This, however, varies with age. The cerebellum weighs about five or six ounces, and is therefore about the seventh part only of the weight of the brain.

The brain (cerebrum) is divided above and before into two lateral halves, named hemispheres (hemisphaeria), right and left, separated by a deep furrow, in which the vertical, crescentic, or dichotomous portion (falsa) of the hard membrane is received. Each hemisphere is bounded by a superior or convex, an inner or plane, and an inferior convex and concave surface. The lower surface of each hemisphere, also, anatomists distinguish into three lobes, an anterior, posterior, and middle.

The cerebellum is also divided into two hemispheres, separated by a middle furrow of less depth, receiving, as that of the brain, a crescentic production, smaller in size, from the hard membrane.

The exterior surface of the convoluted division is formed into eminences longitudinal and rounded, but directed in various ways, named convolutions or circumvolutions (gyri, Soemmering, Wenzel), and separated from each other by deep hollows (sulci). To see this surface, which is termed the convoluted, the vascular membrane termed pia mater (meninx tenuis) must be removed.

The convoluted surface of each hemisphere may be divided into five regions: 1. The commutual or dichotomous; 2. The lateral-superior or convex; 3. The antero-inferior or frontal; 4. The medio-inferior or spheno-temporal; and 5. The posterior or cerebellar region.

1. The commutual, plane, of a shape nearly semicircular, forms the mesial boundary of each hemisphere, and corresponds to the falciform or dichotomous portion of the hard membrane (παράστημα, meninx dura), by which it is separated from the similar surface of the opposite hemisphere. Before and behind it extends from the superior to the inferior surface of the brain; but a considerable portion of its middle is terminated by the upper surface of the middle band (mesobole, corpus callosum), which lies between the two hemispheres. It is contained between the semicircular and the rectilinear margins.

2. The convex region occupies the anterior, upper, lateral, and posterior parts of the hemisphere, from their anterior to their posterior extremity, and from the semicircular margin to a line which extends between these extremities along the lateral borders of the organ.

3. The antero-inferior or frontal rests on the horizontal part of the frontal and ethmoid bones, commencing before with a curved outline, bounded behind by the curvilinear hollow named the fissure of Sylvius, and at its inner or mesial margin by the great fissure which separates the hemispheres. This inner margin presents one convolution, consisting of a longitudinal eminence, extending in the adult brain about 1/2 inch from the posterior towards the anterior end of the notch. The outer furrow contains the cerebral portion of the first pair or olfactory nerves. (1, 1.)

4. The medio-inferior or spheno-temporal is situated immediately behind this region, from which it is separated by the curvilinear hollow (fosea Sylvi). In the ordinary descriptions this forms the middle lobe; while the posterior part, corresponding to the cerebellum, though distinguished by no evident limit, is with equal impropriety named the posterior lobe. The whole region, from the curvilinear hollow to the posterior tip of the hemisphere, may, however, be subdivided into two, the medio-inferior and postero-inferior regions of the convoluted surface, according as they correspond to different containing parts.

5. The posterior cerebellar region of the convoluted surface, which is plane, corresponds to the horizontal or cerebellar part of the hard membrane.

The convoluted surface is formed of cerebral matter, of a gray or dirty wax colour, the surface of which is smooth and polished where it has not been rent by the removal of the membranes and their attachments. In the furrows are many minute orifices, into which the soft membrane (ἀσθμα, παράστημα, meninx tenuis, pia mater) transmits filamentous bodies, containing minute blood-vessels.

Neither the eminences nor the hollows are uniform in number or distribution; and in no two brains is it possible to trace any similarity in their figure, presence, or direction, in the upper, lateral, and posterior part of the convoluted surface, unless where it approaches the central or figurate surface, where a number of important objects are presented.

The convoluted surface communicates with another interior surface at two parts: 1st, on the middle plane, under the posterior end of the middle band or mesobole (corpus callosum); 2d, on each side of the middle plane, at the outer margin of the fluted masses termed limbs of the brain (crura cerebri), between these limbs and the posterior end of the optic chamber or couch (thalamus opticus). This surface of the organ may be termed the central or figurate.

The exterior surface of the cerebellum consists of thin laminated portions of cerebral substance named plates (laminae), or surface of leaves (folia), placed contiguously, either parallel or concentric, and separated by furrows of various depth. This surface, which may be named the laminar or foliated surface of the small brain, communicates also with the figurate surface,—1st, above on the middle plane, between the semilunar notch behind, and the white cerebral plate termed Vietssonian valve before; 2d, at its inferior surface, between the almonds or spinal lobules above, and the upper end (medulla oblongata) of the spinal chord below.

The outline of each hemispherical surface of the cerebellum describes three fourths of a circle; and as the segments mutually meet towards the mesial plane, the mode of union varies according to the figure of the objects to which they are adapted. 1st, The hemispherical border, approaching the anterior part of the organ, is suddenly interrupted where the cerebellar peduncles (crura cerebri) are connected with the protuberance; and, pursuing a retrograde direction on each side towards the mesial plane, forms a re-entrant curvature or notch—the semilunar—Semilunar corresponding to the lower pair of the bigeminous bodies, notch. 2d, The hemispherical borders, approaching the posterior part of the cerebellum, proceed, near the mesial plane, by an acute circular turn, almost straight backwards, and form, at the posterior edge of the organ, a deep rectangular notch, Y, not unlike the figure of the ancient Purse-like lyre, named the perpendicular fissure of Malacarne, or notch, the purse-like fissure of Reil, and containing the cerebellar vertical portion of the hard membrane (falsa cerebri). Between these two boundaries the cerebellar plates, of which the hemispheres consist, are united in the middle by an interlace, named suture (raphe), of the cerebellum. A large hollow between the hemispheres, extending backwards from the semilunar to the purse-like fissure, is the small valley (callecula) of Haller. Each hemispherical surface consists of five lobes: 1. the anterior-upper or quadrilateral; 2. the posterior-upper; 3. the posterior-lower; 4. the slender, rarely exceeding three lines in breadth; 5. the two-bellied or biventral; and 6. the central lobe. The first two belong to the upper or flat hemispherical surface; the next three to the lower or convex hemispherical surface; and the sixth, common to the two hemispheres, is situated on the mesial plane of the upper surface, between the anterior end of the middle line (raphe) and the middle or apex of the semilunar fissure.

The biventral lobe is pointed, and its margin concave; and between this margin and the parts of which the valley consists is placed a group of plates, convex and rounded, named the tonsil or tonsils (tonsillae; amygdalae; the spinal lobule of Gordon).

In the angular hollow between the biventral lobe and the peduncle (crus) of the small brain, is the flock, a minute body, of irregular shape. Each flock consists of six or seven plates (laminae), starting directly from the beginning of the peduncle, and with the concave margins directed towards the protuberance.

The valley is distinguished into three bodies, the pyramid, uvula, and nodulus. The first is a group of 20 parallel plates, with a triangular apex, bounded behind by the purse-shaped notch, and before by another cluster of plates called the uvula. The uvula, which is anterior, consists of twelve laminated leaves, is six lines long and four broad, and is smaller than the pyramid, and conical, with its base turned to that body. Lastly, anterior to the uvula, and separated from it by a furrow, is the laminar tubercle (tuberculo lamino) or nodule, consisting of about ten thin transverse plates, the smallest in the row.

The second surface of the brain, in situation interior or central, may be named the figurate or symmetrical. Instead of presenting the uniform eminences and hollows which distinguish the convoluted surface, it is moulded into definite shapes, which correspond with each other, as they are situated on opposite sides of the middle plane—or the parts of which, when situated on this plane, are exactly symmetrical. The surface formed by these figured objects bounds what are termed the ventricles or cavities of the brain. They cannot justly be termed cavities any more than the hollows between the convolutions, but ought to be viewed as continuations of the exterior or convoluted surface.

The central or figurate surface of the brain presents the following objects. The central band, beam, or mesolobe, a mass of white cerebral matter, uniting both hemispheres on the mesial plane, with the twinband or vault below; the hippocampus major on each side; the anterior pyriform eminence or striated body on each side; the posterior pyriform eminence or optic chamber on each side; the semicircular band on each side; the ergot on each side; the comarium on the mesial plane; the bigeminous eminences on the mesial plane; the valve on the mesial plane; and its pillars on each side.

The commutual or dichotomous region of the convoluted surface is terminated below by the upper surface of a white band uniting the two hemispheres. This, which was named by the ancient anatomists the smooth or polished body (σύρα τελευτική; corpus lacer), to distinguish it from surfaces formed by a cutting instrument, appears in the form of white fibrous matter, passing transversely between the hemispheres, and marked by three longitudinal lines, one on the mesial plane, and one on each side. This is the middle or central band (mesolobe of Chaussier). Near its middle is a bundle of gray lines, which may be traced to the central portion of the hippocampus major.

The posterior extremity of this body is rounded, and communicates with the chamber named third or middle ventricle. This surface is continued forward, and forms the vault or ceiling (fornix, Die Zwillingssbinde, the twin-band, Reil). The names of callous body and vault are used, as if they were denominations of different bodies. If they are still retained, it ought to be stated that they are names applied to opposite surfaces of the same object.

The relations of the posterior end of the middle band are as follow. The handle of a scalpel inserted beneath it is found to be in the middle ventricle, with the vault above, the comarium or pineal body, and four eminences of the upper surface of the protuberance (corpora bigemina) below, and a part of each optic chamber on each side. The vault or inferior surface of the band has the shape of an isosceles triangle, with the base behind. Before it is incurvated downward as it becomes narrow; and the space between the hand and it is occupied by a thin double plate of cerebral matter, separating the two ventricles, and named the diaphanous partition (septum lucidum). (s., s., s.) The fornix terminates before, in two bodies named anterior pillars. (Fig. 3, r., r.)

The posterior end of the middle band penetrates into the substance of the hemispheres; but the gray chords already noticed, pursuing their lateral course, are immediately enveloped in white plates derived from the sides of the vault, and assuming a cylindrical appearance, form, opposite the cerebral limbs, a body with a free superior rounded surface, which bends in a curvilinear direction lateral and downwards, and is the great hippocampus or communicylindroid process. (Chaussier.) In observing this curvilinear course, it rests on and corresponds, but without adhesion, to the upper margin of the cerebral limb as it issues from the optic chamber; and the surfaces of both parts, though kept in apposition by vascular membrane, are free and unadherent. It forms the great cerebral fissure of Bichat.

The hippocampus, therefore, consists of two parts. The first, which is the gray indented band (le corps godronné, Vicq-d’Azyr), is an inner or central portion, as thick as a large crow-quill, gray in colour, indented at the free edge, adhering to the cerebral substance by its opposite margin, and connected with the upper surface of the central band. The outer or second part, which is a broad thin plate of white cerebral matter folded over the gray indented band, as a map is rolled over a cylinder of wood, known under the name of the tape or fringe of the hippocampus, is connected with the lower surface of the same central band, or the vault (fornix) of the brain.

At the inferior region the communication is effected inferior by the curvilinear hollow. (Fig. 1, s., s.) This presents, 1st lateral cerebral substance, penetrated by numerous holes of various size, named the white perforated substance (lamina perforata); 2dly, the unconvoluted space; 3dly, the long cerebral band termed the optic tract; and, 4thly, the limb of the brain. This body, with that of the opposite side, is covered by a portion of the convoluted surface, the inner and prominent surface of the medio-inferior or spheno-temporal region.

The convoluted surface, which covers the anterior end and outer margin of the cerebral limb, when everted, presents the thin white body named the tape or fringe (tenuis) of the hippocampus; and if the portion of convoluted brain next the curvilinear hollow be raised and everted in the same manner, the anterior end of this object, termed the foot (pes hippocampi), comes into view. The fringe of the hippocampus forms, in the natural position of the organ, the outer and lower border of the opening; while the limb of the brain, and the outer Special Anatomy.

The striated eminences.

When the central surface is exposed by removing the central band and the vault and ceiling of the ventricles, two pyriform eminences, an anterior and posterior, come into view. The anterior is ash-colored or gray, inclining to wood-brown, with the round convex extremity before, and the small end tapering backwards and outwards, so as to inclose the round end of the posterior eminence. The surface is smooth and convex, consisting of a thin covering of gray cerebral matter. The interior consists of an admixture of white and gray, so as to form alternate streaks—a circumstance from which these eminences on each side have been named the striated bodies (corpora striata). At their anterior mesial extremity are two rounded vertical bodies of white cerebral matter, descending from the anterior end of the vault. These are the anterior pillars, which are thus interposed between the interior front of the striated bodies.

The posterior and internal margin of the striated bodies is bounded by a gray, hard eminence, about a line broad, stretching with a sinuous or winding direction from its mesial and anterior to its external lateral and posterior margin. This is the semicircular fillet or band (tænia semicircularis, centrum semicirculare geminum). Always firmer than the neighboring parts, it appears to be the external margin of a gray-colored stratum or wall of cerebral matter between the anterior and posterior pyriform bodies.

Connected before and on the outside to the striated body by means of the double semicircular chord (centrum semicirculare geminum, Vieussens), each optic eminence presents four free surfaces—the upper, the inner, the posterior, and the lower. The upper is gently rounded, convex, and white in color; its limits are not easily defined. The outer margin is bounded by the circular band, which even passes anterior to it, so as to form its boundary in that direction also. Behind, it is less distinctly limited, unless by the appearance of a considerable prominence, named the posterior tubercle of the optic couch.

The inner margin of the upper surface is distinctly marked by a small, sharp, gray line, which, beginning insensibly at the anterior part of the body, becomes more distinct as it extends backwards, and ultimately bends towards the median plane. There it unites with a similar elevated line of the opposite optic eminence; and to the point of union is attached a small conical body with a minute point, of a gray color, and of a shape like that of the pine-apple. This is the pineal gland (glandula pinealis, conarium); and the minute linear eminences which form the inner edge of the upper optic surface have been named peduncles of the pineal gland.

The inner surface of the optic couch or chamber presents the small portion of soft cerebral matter (commissura mollis) which unites it to the similar surface of the opposite body; and the intermediate space between the inner surfaces of these bodies on each side constitutes the third or middle ventricle (ventriculus tertius). Its posterior edge, however, is terminated by the cerebral limb of that side; and the lower edge meets that of the opposite one, and is connected to it by a portion of brain which forms the lower part of the middle ventricle, and corresponds on the outside to the bridge of Tarin (pons Tarini).

The posterior surface of the optic chamber is convex and continuous with the unconvoluted space. It most convex part presents two oblong roundish eminences, separated by a linear depression, which may be traced downwards with an outward curvature, and forwards about five or six lines, in a broad white band, crossing two fluted masses mutually converging behind at an angle. These eminences are the geniculate bodies (corpus geniculatum externum et internum), the outer the largest of the two (fig. 1, g, g); the white bands are the optic tracts or origins of the optic nerve, issuing from the geniculate tubercles (o, t); and the fluted converging masses are the limbs of the brain (crura cerebri).

On the inner or mesial side of the geniculate bodies, bigeminal and separated only by a linear furrow, are the bigemino-eminentia, four orbicular elevations, two above and two below; two on each side of the mesial plane, with an intermediate cruciform furrow. By the ancients, who examined chiefly brute animals, the superior and larger pair were named mates (γάσπαρες), the inferior testes (ειδώλη). These eminences occupy the upper surface of the protuberance, and partly that of the limbs of the brain; and while the eminences are situated between the posterior ends of the optic chambers above, the limbs appear to issue from the centre of these chambers below, and the linear furrow marks the point of junction.

These bigeminal eminences, however, though occupying the superior surface of the protuberance, adhere not everywhere to its substance. (Fig. 3.) The mesial furrow is formed on the upper surface of a thin plate of white cerebral matter, which extends from the level of the pineal peduncles above, to the upper margin of the cerebellum below, like a veil, and is named the cerebral valve (valvula Vieussensi). The lower surface of this is free for about two or three lines broad; and, though applied to a similar surface on the mesial line of the upper region of the protuberance, does not adhere, but forms a canal with the third ventricle above and the fourth below, named the aqueduct of Sylvius (iter a tertio ad quartum ventriculum) (i). While the outer halves, therefore, of the eminences adhere to the matter of the protuberance, the inner are attached to that of the valve. (n, t.)

The lower or cerebellar margin of the valve is free, and Pillars of overhangs as it were the fourth or cerebellar ventricle, the valve. On each side, however, is a longitudinal rounded body of white matter, which passes from the lower pair of bigemino-eminentia (testes) to the cerebellum. These are named the pillars of the valve (columna valvula Vieussensi, processus a cerebello ad testes). The fourth or pathetic nerve (trochlearis) rises partly from the valve, partly from its lateral pillars, and is seen issuing on the sides of the protuberance not larger than a thread.

The lower surface of the optic chambers presents within the convoluted space the limbs of the brain (crura cerebri), two fluted semicylindrical masses, converging backwards, and inclosing by their junction a triangular space, with the apex behind—the intercerebral hollow. The inner margin of the limbs presents the origin of the third or oculo-muscular nerves (oculo-motorii); about half an inch anterior on the intercerebral hollow are the lenticular or pisiform bodies (tubera, v. corpora candelantica), two hemispherical tubercles of white matter; and immediately anterior is the hypophysis or pituitary gland, a broad quadrilateral reddish-gray prominence, with the anterior margin rounded, the posterior concave, inclosed before and on the sides by the converging optic tracts and commissure. (r.)

The limbs are obliquely crossed at their outer anterior end by the broad part of the optic tracts as they descend from the geniculate bodies. Their posterior convergent extremities are lost in the substance of the annular protuberance (pons Varolii, nodus cerebri), a convex rounded white body, with transverse fasciculi separated by linear furrows. (s.) Connected before with the crura or limbs, from which it is separated by transverse sinuous furrows, it is connected on the sides with the cerebellum by short semicylindrical stalks or peduncles (crura cerebri), and Special Anatomy behind with the beginning of the spinal chord (medulla oblongata). It is marked on the middle by a longitudinal furrow, in which is placed the basilar artery, the united trunk of the vertebrae. Its convexity corresponds to the concavity of the basilar groove of the occipital bone, on which it rests. This eminence may be regarded as the general central point of the cerebral nervous system, with which all the other parts are connected,—with the cerebral hemispheres by the crura cerebri, with the cerebellar hemispheres by the crura cerebri, with the upper internal part of the optic chambers by the bigeminous eminences, and with the spinal chord by the medulla oblongata. From its anterior lateral margin the tergeminal or fifth nerve arises; from the posterior furrow the abducent or sixth nerve; and from the upper anterior margin of the cerebellar peduncle the eighth or lateral facial.

Continuous with and behind the protuberance is the beginning or bulb of the spinal chord, a part distinguished on the ground of an obsolete hypothesis by the name of medulla oblongata. Thick and prominent, its surface is moulded into six oblong-ovoidal eminences, three on each side of the mesial plane; the pyriform or pyramidal eminences before, the restiform bodies behind, and the olivary eminences on each side.

The pyriform eminences (corpora pyramidalia) are two oblong-oval bodies, broad above, tapering below, separated by a mesial line, and bounded laterally by a furrow separating them from the olivary bodies, occupying the anterior-inferior part of the bulb of the chord, and resting on the lower third of the basilar groove. The mesial line terminates above in the foramen caecum of the posterior furrow of the protuberance. (v.)

The olivary (corpora ovata), placed on the outside of the pyramidal bodies, occupying partly the front, partly the side of the bulb, give it a lateral and transverse projection. In the intermediate furrow are the initial filaments of the hypoglossal or middle lingual nerve; and in the external furrow and sides those of the glossopharyngeal and pneumogastric nerves. (o.o.)

The posterior-upper part of the medulla oblongata consists of two longitudinal cylindrical bodies, stretching between the cerebellar peduncles above and the spinal chord below. These are the chordal processes of Ridley, the restiform or rod-like processes of Morgagni, the pyramidal bodies of Haller, Malacarne, and Reil, and the posterior pyramidal bodies of Ruysch, Prochaska, and Soemmerring. Above, where they are connected with the cerebellar peduncles, they are separated by a triangular space with the apex downward, but below by a deep furrow, the colamus scriptorius of the ancients, at the bottom of which, when separated, may be observed white chords proceeding from the process of one side, plaited with those of the other. These decussating fibres, which are confined entirely to the mesial margin of the restiform processes, are believed to establish a crossing connection between the right and left sides of the peduncles and the protuberance. The intermediate cavity is named the fourth ventricle. From the inner surface of the restiform process issue several of the initial filaments of the seventh or auditory nerve.

The spinal chord or funicular brain is a cylindrical body occupying the interior of the vertebral canal, from the margin of the occipital hole to the first lumbar vertebra; large and round on the cervical region, broad on the dorsal, and terminating in a brush-like expansion, denominated the cauda equina. On its dorsal surface may be seen a slightly depressed line continued from the middle furrow of the restiform bodies, but becoming faint and indistinct in the region of the back.

The central or figurate surface is smooth, polished, and possesses a degree of closeness of texture which prevents it from being readily abraded. These qualities are ascribed by Reil to a thin pellicle, which he terms epithelia. Though there is no proof of the existence of the covering, the term may be used to designate the smooth surface of the organ.

Of the central surface not only does every division mutually communicate, but the central surface of the convoluted communicates with that of the laminated part of the organ. The lateral divisions, named ventricles, communicate directly with each other below the vault, the surface of which lies over the thalamus; both communicate with the third ventricle, which by the Sylvian aqueduct communicates with the fourth; and the posterior part of the lateral ventricle communicates with the digital cavity and inferior recess.

The central surface is covered by a vascular membrane (plexus choroides), continued from the pia mater of the convoluted surface.

Between the two surfaces now described is placed the proper matter of the brain, white and brown, which in different regions of the organ is differently arranged.

The convoluted surface consists of a stratum of gray cerebral matter, arranged in the granular form. When indurated by immersion in alcohol or dilute nitric acid, it breaks with a small conchoidal fracture, occasionally uneven, and with an uneven granular surface, void of lustre and without fibrous arrangement. The only part of the convoluted surface presenting the latter appearance is the unicum band uniting the anterior and posterior lobes. (Fig. 5, v.)

Within the convoluted surface is contained a large quantity of white matter, surrounding the figurate surface and its divisions. The section of this, usually named the oval centre of Vieuxsenius (centrum ovale), shows merely the extent which this occupies in the upper part of the brain, but communicates no information on the intimate structure of the organ.

In intimate organization the brain may be distinguished into four parts; 1st, the brain, containing the striated nucleus; 2d, the cerebellum, containing the moriform body; 3d, the head or bulb of the chord, containing the moriform body; and, 4th, the annular protuberance as a central point of the whole.

The white fibrous matter of the central band, passing into the hemispheres on each side, diverges like the rods of a fan or the rays of a luminous body, and forms an arrangement denominated by Reil the radiating crown, and which may be regarded as the exterior investment of the striated nucleus, which constitutes the internal substance of the striated bodies and optic chambers. (Fig. 5, c.) The arrangement of white and gray matter in this part is so peculiar, that within the limits of this sketch it is impossible to convey a distinct idea of it. It may be stated in general that the fibrous matter of the limbs extends from the protuberance through the substance of the thalamus and part of the striated body; and while in this manner it maintains a connection between the protuberance and the brain above, by means of the cerebellar peduncles on the sides, and the head of the chord below, it communicates with the cerebellum and spinal chord behind and below. The moriform bodies (corpora dentata, corpora ciliata, corpora rhomboidea), which consist of white matter inclosed in a brown capsule, and the cerebellar and olivary eminences, are analogous to the striated nucleus of the brain; and the three may be regarded as the respective centres of each. The annular protuberance, consisting internally of transverse fibres closely interwoven with longitudinal ones, is the general or common centre of the three. The substance of the funicular or vertebral portion consists almost entirely of white fibrous matter, extending longitudinally from the cranial to the sacral extremity, but bending off laterally at the origins of the spinal nerves in the form of arches.

The brain is supplied with blood by the internal carotid arteries and the two vertebral arteries, derived from the subclavian. The former, entering the cranium by the carotic canals, sends a posterior communicating branch, inosculating with the principal division of the basilar, and an anterior communicating, which joins the vessel of the opposite side. By these communications, the branches of the basilar artery behind, and the carotids before, form an arterial hexagon round the sella Turcica, from which arise two anterior vessels (anteriores cerebri), distributed to the central band, and two lateral (mediae) or Sylvian arteries, distributed to the perforated spot, the Sylvian fissure and striated nucleus. The vertebral, entering by the occipital hole, send branches to the head of the spinal chord, and uniting to form the basilar, supply the protuberance and cerebellum; then divericating into posterior cerebral, finally inosculate with the internal carotid to form the arterial hexagon as mentioned. The blood is returned by triangular canals named sinuses, of which there are the superior longitudinal, the inferior longitudinal, the cerebellar (torcular Herophili), the lateral, the circular, the superior petrous, the inferior petrous, and the cavernous. The four latter pairs are small sinuses opening into the lateral, where it emerges from the cranium by the temporo-occipital fissure (foramen lacrum in base crani posterior).

§ 2. THE CEREBRAL INVESTMENTS OR MEMBRANES.

The brain is said to be surrounded by three membranous envelopes, the hard membrane (meninx dura, dura mater), the web-like membrane (tunica arachnoidea), and the soft or thin membrane (meninx tenuis, pia mater). To this arrangement, which has been adopted by almost all writers, there is perhaps no great objection. But it simplifies the subject, without misrepresenting, to refer them to two only; one of which, the hard membrane (meninx dura, meninx durae, dura mater), is common to the brain with the inner surface of the skull; the other, the thin membrane (meninx tenuis, meninx tenue, pia mater), is proper to the brain only. They may be distinguished, therefore, by the terms common membrane of the brain and proper membrane of the brain. The arachnoid, again, is a pellucid web common to the cerebral membranes.

The first of these, the common or hard cerebral membrane (meninx dura, dura mater), presents two surfaces, an outer or cranial and an inner or cerebral. The outer surface is irregular, filamentous, and vascular, and the substance of which it consists is distinctly fibrous. The fibres, however, do not follow any uniform direction, but are interwoven irregularly. Maceration causes this membrane to swell and become separated into fibrous threads. It is liberally supplied with blood-vessels, by which it is connected to the inner surface of the skull. No nerves or absorbents have been discovered in it. This outer or cranial surface of the dura mater is of the nature of periosteum. Its vessels may be traced into the inner table; it contributes to the formation of the cranial bones in the fetus, and their nutrition during life.

The inner or cerebral surface of this membrane is smooth, polished, and shining; and, when examined in water, it appears to be formed by a very thin, transparent membrane, through which the cranial or outer surface and the fibrous structure of the hard membrane may be recognised. This pellucid inner membrane, generally termed the inner lamina, is the exterior division of the arachnoid membrane.

The dura mater is an extensive membrane, lining not only the interior surface of the skull, but, in a modified form, that of the whole vertebral column. The inner surface of each vertebra has a proper periosteum continuous with the periosteum of the outer surface; and from this issues a quantity of filamentous tissue, which penetrates directly a membranous canal, evidently of fibrous structure (theca vertebralis), tough and firm, but more delicate than the cranial dura mater. The dura mater in its course forms sundry prolongations; for instance, the large crescentic one named the falx, the horizontal one termed tentorium, and the small crescentic one named falx minor or cerebri.

The thin, soft, or immediate and proper cerebral membrane (pia mater, meninx tenuis) presents in like manner two surfaces, a smooth or cranial, which is exterior, and a filamentous or cerebral, which is interior and central.

The outer or smooth surface of the thin membrane (pia mater) has a glistening appearance, and is formed by a very thin transparent membrane, exactly similar to that which forms the cerebral surface of the dura mater. This surface, named in the ordinary works the web-like membrane (tunica arachnoidea), is believed to be a separate membrane from the pia mater; but that which forms the inner or cerebral surface of the dura mater has a claim equally strong to this distinction.

The inner or cerebral surface of the proper membrane is filamentous, flocculent, and sends out many angular filamentous processes, which, by numerous minute arteries and veins, communicate with the convoluted surface of the brain. These processes (omentum) correspond to the furrows of the convoluted surface in which they are lodged. In detaching the membrane from this part of the brain, numerous vessels are drawn out of its substance; and when the membrane is injected these vessels may be seen distinctly filled, and communicating with the gray matter of the convoluted surface. The veins of this membrane may be traced to the sinuses. Neither nerves nor absorbents have yet been recognised in it. Bielat considers it to contain much cellular tissue, which, however, is denied by Gordon, who could not recognise it. The difference, however, consists merely in name. The pia mater, indeed, possesses no cellular tissue like the subcutaneous, the submucous, or the subcorneous. If, however, a portion of the arachnoid be peeled from it by careful management of the forceps and blowpipe, there is found a quantity of loose filamentous matter uniting this tissue to the fine web of the former. The existence of this tissue between the pia mater and arachnoid is further demonstrated by the phenomena of serous infiltration.

The pia mater, or proper membrane of the brain, consists of two parts, an outer, covering the convoluted surface of the brain, and an inner or central, entering the cavities formed by the inner, central, or figurate surface, and spread over this surface in the form of what has been termed the vascular or choroid web (plexus choroides; tela choroidica).

The continuity of the pia mater or exterior division of the proper cerebral membrane, with the choroid plexus or interior division, may be demonstrated in the following manner. First, The pia mater may be traced behind and below the posterior extremity of the middle band (corpus callosum, der balken), where it is continuous with the transverse web called velum interpositum, and which may be regarded as the first part of the central division. Secondly, From the situation of the velum interpositum, it may be traced forwards on both sides of the Special mesial plane into the lateral ventricles, spread over the surface of the optic thalamus and striated eminence in the form of the vascular web called choroid plexus, the right half of which communicates with the left by means of a similar slip of vascular membrane lying beneath the vault (formix), and behind the anterior pillars of that body at the spot termed foramen Monroianum. Thirdly, It may be traced over the geniculate bodies and thalami into the posterior-inferior cornu, or sinuosity of the lateral ventricle, where it covers the great hippocampus. Fourthly, It may be traced at the angle between the cerebellum and medulla oblongata, or what is named the bottom of the fourth ventricle, where it forms a very minute choroid plexus, seldom noticed by anatomists, but not less distinct, and which may be traced up the fourth ventricle to be connected with the velum interpositum in the middle ventricle, and with the lateral portions of the hippocampus on each side. Each of the divisions of the choroid plexus now enumerated may be shown to be mutually connected, and to form parts of one general membrane, which again constitutes the inner or central division of the membrane of which the pia mater forms the exterior. Each division of the choroid plexus, in like manner, is connected, by means of minute blood-vessels, to the portion of the figurate cerebral surface on which it rests; and it appears to sustain vessels as the pia mater does to the convoluted surface.

In clear water the choroid plexus may be spread out, like the pia mater, in the shape of a thin semitransparent web, one surface of which is smooth, the other somewhat flocculent, and the substance of which is traversed by numerous minute vessels. The transparent web, which forms the basis of this membrane, is filamento-vascular; and its smooth free surface, a continuation of the arachnoid membrane, is smooth, polished, and thin, like silver paper.

The arachnoid membrane is common to the dura mater, pia mater, and choroid plexus. It covers the inner surface of the first membrane, to which it communicates its shining polished appearance, though the want of subjacent filamentous tissue causes it to adhere so firmly, that it cannot be readily demonstrated. After covering the free surface of the pia mater, it follows the course of that membrane into the central surface of the brain, and covers the upper or unadherent surface of the several divisions of the choroid plexus. For the demonstration of this fact we must be permitted to refer to Dr Craigie's Elements of General Anatomy (chap. xxiii, sect. I), where the reader will find proofs, which the limits of this sketch do not allow us to adduce here.

From these it results that the arachnoid membrane possesses in arrangement and distribution a great resemblance to the serous membranes. It differs, nevertheless, in its extreme tenacity, in the closeness with which it adheres to the collateral tissues, and in its slight disposition to albuminous exudation. It appears to contain in its structure less filamentous tissue than the pure serous membranes.

The brain is developed from the branches of the internal carotid and vertebral arteries ramified through the vascular membrane (pia mater). Formation commences in two orders of vessels mutually directed to each other,—those of the convoluted surface (pia mater), and those of the central (plexus choroides). The central substance of each part is first deposited; and from these points deposition and moulding proceed to the two circumferences of the organ. The surfaces are therefore formed last; and the vessels gradually shrink as the process approaches to completion.

**Sect. II.—The Distributed Chords; The Nerves.**

The nerves may be distinguished into classes according to the parts of the brain with which their cerebral ends are connected. On this principle they may be arranged in the following order.

| Protuberance or its parts | 1st pair. | |--------------------------|---------| | Olfactory | | | Optic | 2nd pair. | | Oculo-muscular | 3rd pair. | | Trochlear (nerve patheticus) | 4th pair. | | Trifacial, 5th pair | | | Abducens | 6th pair. | | Auditory | 7th pair (portio molle). | | Lateral-facial | 8th pair (portio dura). | | Glosso-pharyngeal | 9th pair. | | Pneumogastric | 10th pair (nerve vagus). | | Accessory | 11th pair. | | Hypoglossal | 12th pair. | | Sub-occipital | | | Cervical nerves | | | Dorsal | | | Lumbar | |

The spinal nerves are derived from anterior and posterior roots separated by the ligamentum denticulation, a fibrous notched ligament, covered by arachnoid membrane. According to the researches of Charles Bell and Magendie, the anterior roots furnish motive filaments, and the posterior sensitive. The central connections of most of these nerves have been already mentioned; and their distributed connections have been, and will continue to be, incidentally noticed under the heads of the several organs. It is requisite, however, to notice shortly the relations and general distribution of several nervous chords which perform an important part in the functions of the animal body. These are the pneumogastric, the phrenic, and the great sympathetic or intercostal nerves.

The pneumogastric or nerve vagus, the 10th pair of the Pneumold nomenclature, the 10th in correct enumeration of the gastric cerebral nerves, rising by various filaments from the furrow between the olivary bodies and the restiform, and from the posterior upper surface of the latter, emerges from the cranium with the jugular vein by the temporoparietal hole. Here, closely united by filamentous tissue to the hypoglossal, spinal, and glosso-pharyngeal, it descends before the rectus anticus and longus colli on the outside of the carotid artery, though in the sheath with it, and before the subclavian artery on the right side, on the left before the carotid, enters the chest, where it enlarges in size considerably. (Plate XXXI. v, v.) In the chest it passes behind the bronchi in the posterior fold of the pleura, and is closely connected to the oesophagus in the shape of a thin cord. Both trunks, on reaching the cardiac end of this tube, pass with it through the diaphragmatic aperture, and are distributed to the stomach. In this course the pneumogastric nerve is divided into five orders of filaments.

1. In the neck it gives branches to the pharynx, and, communicating with the glosso-pharyngeal, forms the pharyngeal plexus, and furnishes a superior laryngeal branch, an external laryngeal, and an internal laryngeal, the latter chiefly to the intrinsic muscles of the larynx.

2. In the chest it sends off branches, which, communicating with those of the superior cervical ganglion, are distributed to the heart.

3. In the chest also it gives off the inferior laryngeal or recurrent nerve (r), which on the right side winding round the subclavian, on the left the arch of the aorta, rises in the lateral furrow between the windpipe and oesophagus, and giving off cardiac, pulmonary, oesophageal, thyroid, and tracheal filaments, is finally distributed to the intrinsic muscles of the laryngeal cartilages. These multiplied connections tend to associate the motions of the glottis with the lungs, and to maintain a general consent between the pharynx, larynx, oesophagus, trachea, lungs, and heart. 4. The pneumogastric trunk forms with the filaments of the inferior cervical ganglion the anterior pulmonary plexus, and alone it forms the posterior pulmonary plexus, which sends filaments to the lower part of the windpipe, the bronchi, the pulmonary artery and veins, and the oesophagus.

5. After passing the diaphragmatic aperture, the right pneumogastric trunk forms at the cardiac orifice of the stomach a plexus, from which filaments proceed to the pylorus, the gastro-hepatic artery, the right celiac ganglion, the duodenum, the pancreas, the gall-bladder, and the liver, where it communicates freely with the celiac ganglions. The pneumogastric of the left side is distributed chiefly to the pylorus and its arteries, and communicates freely with those of the right.

The phrenic nerve, connected above with filaments of the pneumogastric, hypoglossal, second and third cervical nerves, and some branches of the brachial plexus, and occasionally with those of the great sympathetic, descends on the anterior and lateral part of the neck, between the rectus anticus and scalenus anticus, and enters the chest between the subclavian artery and vein. The right passes down on the surface of the right lung, beneath the pleura (§, §, Plate XXXI); the left over the pericardium; and both are distributed chiefly to the diaphragm.

The great sympathetic is much more complicated than either of these nerves. It cannot be said to originate from one part more than from another. Though connected with the brain by means of a communicating filament of the sixth pair, it certainly does not arise from that nerve; nor can it be said to arise from the spinal nerves, though connected with them on each side of the dorsal vertebrae. It appears more rational to regard it as a general and extensive network of nervous filaments, which establish a communication between different important organs. Connected above with three ganglions of the neck, the superior, inferior, and middle cervical, and by minute filaments with the lateral-facial, or eighth cerebral, pneumogastric, and glossopharyngeal, with which it contributes to form the pharyngeal plexus, it sends off the nervus molles or superficial cardiac nerve. Below the inferior cervical ganglion, generally regarded as a cardiac, the trunk enlarges, and furnishes filaments to the pulmonary and celiac plexus, the former divided into right or anterior and left or posterior, and the latter into superior and inferior. About the seventh dorsal vertebra, after being connected with all the intercostal nerves and inferior thoracic ganglions, it forms the splanchnic, which, though only the abdominal part of the great sympathetic, may be regarded as a separate nerve. The constituent filaments of this nerve, after being united into two ganglions, the celiac or semilunar, are resolved into plexiform arrangements, which surround all the principal arteries, and with them are lost in the substance of the organs. Thus the celiac artery is inclosed by the celiac plexus; and each of its divisions, the coronary or proper gastric and the gastro-hepatic and gastro-splenic, are inclosed in similar plexiform networks. In the same manner, the superior mesenteric, inferior mesenteric, and renal arteries, have each an appropriate plexus; and those of the colon, bladder, and uterus have small plexiform arrangements, which constitute parts of the same general system. In short, the great sympathetic or intercostal forms an independent nervous system of its own, and though not derived from the dorsal nerves, is intimately connected with them; and its distribution to the organs of digestion, of circulation, respiration, and secretion, is connected chiefly with the associated actions of these organs.

Our limits do not, however, admit of details; and the reader who wishes to understand the minute anatomical relations of these chords, will find the most accurate information in the fourth volume of the treatise of Soemmerring (De Corporis Humani Fabrica, Trajecti ad Rhenum 1798); in the third of the Descriptive System of Bichat, and in the magnificent illustrations of Walter (Tabula Nervorum Thoracis et Abdominis, fol. Berolini, 1783) and Scarpa (Tabulae Neurologicae, fol. Ticini, 1794).

PART II.

ANATOMY OF THE ORGANS PERTAINING TO THE ENTROPHIC OR NUTRITIVE FUNCTIONS.

The growth of the animal body is effected, and its size and strength maintained, by a class of organs which may be named the Entrophic or Nutritive. These organs agree in the possession of certain common characters, by which they are distinguished from those of the functions of Relation.

The first common character is the want of symmetry in arrangement and harmony in action. Instead of being arranged on the median line, or with similar parts on each of its sides, the organ, or part of the organ, which is on one side, bears no resemblance to that which is on the other. Even in the case of the lungs, though there is a general resemblance, the left differs from the right not only in size and shape, but in the number of its lobes.

It must not be understood, nevertheless, that the organs of this class are altogether void of symmetrical figure. A plane may be made to divide the stomach even into similar halves, so as to leave on each side similar parts of the cardia, of the pylorus, and of the intermediate parts. This plane, however, corresponds not with the mesial plane, but passes transversely from left to right. Nearly the same rule is applicable to other organs.

The second general character of the entrophic organs is, that in action they are not under the influence of the will. The contractions of the muscular tissue of the stomach, and the secretion of its mucous surface, the peristaltic motion of the intestinal tube, the beats of the heart, and the action of the liver, are equally independent of volition. This character Bichat attempted in every instance to trace to independence on the influence of the brain and the cerebral nerves. In one sense this is a truism, in so far as it merely implies that the organs of the entrophic functions do not belong to those of relation. In another sense it is a gratuitous, if not a hypothetical assumption. Though the brain is evidently very intimately associated with the organs of the animal functions, it is not yet determined that it is entirely unconnected with those of the entrophic order. Serious lesion or injury of the brain or the protuberance operates as forcibly on the action of the heart as on that of the muscles of the extremities. On the whole, the safest mode of defining this character is merely to state the independence of the entrophic organs on the will.

Several of the organs of the entrophic function are nevertheless in some degree under the influence of the will. The lungs, for example, by being dilated only by the dilating agents of the chest, are within certain limits under the voluntary power. To this, however, a limit is fixed. Though inspiration or expiration may be effected at the will of the individual, or suspended for a little, very soon the accomplishment of these actions is no longer arbitrary. In like manner, though the bladder is evacuated by the voluntary effort of the individual, the stimulus by which the action is induced is involuntary altogether.

A third anatomical character common to the entrophic organs is, that all of them are situate in the interior of the Special trunk, protected by those of the locomotive system; and that they are lined on one side by mucous membrane, continuous with the external integuments. By means of this arrangement, which is necessarily allied with their property of converting foreign into proper matter, all the entrophic organs, with the exception of the heart, communicate with the surface of the body.

A fourth anatomical character common to these organs is, that though continuous by their mucous investment with the outer surface of the body, their opposite, placed on the outside of the serous membranes, forms shut cavities, not communicating, unless in one instance—the peritoneal end of the oviduct in the female—with the external surface. Whatever be the intermediate substance, these organs are placed between the mucous and serous membranes.

The entrophic organs may be distinguished into two orders, according to the degree of the process performed by each. The nutritive function consists of two subordinate functions, the limitrophic or alimentary, and the harmotrophic or circulatory; the first the preparation of the materials destined to be employed in nutrition; the second the distribution of these, after preparation, to the different regions and organs of the system. The organs by which the first process is accomplished constitute the first order; those by which the second is effected constitute the second order.

CHAP. I.—THE LIMITROPHIC ORGANS.

The limitrophic organs consist of two divisions; those for digestion of the food, or the chylopoietic, and those for absorption of its nutritious part. The former is effected in successive processes in the divisions of the alimentary canal, a tubular musculo-membranous apparatus, extending from the mouth to the anus. The second is accomplished by an assemblage of minute valvular tubes, the lacteals, terminating in the thoracic duct.

SECT. I.—THE ORGANS OF DIGESTION; THE CHYLOPOIETIC ORGANS.

The organs of mastication have been described already in the fourth section of the second chapter of Part First.

The pharynx, placed on the median line, symmetrical and regular, occupying the upper part of the neck, makes a close approach to the organs of relation, and marks the transition from these to those of the entrophic function. Attached above to the cuneiform process of the occipital bone, behind to the cervical vertebrae, and with the nostrils, mouth, and larynx before, it forms an irregular vaulted apartment about four inches long and two broad at its widest part, and contracting below, where it is continuous with the oesophagus. Besides the opening into this tube, the pharynx presents six apertures; the pharyngeal apertures of the nostrils, the pharyngeal orifice of the mouth, the upper end of the larynx, and the pharyngeal apertures of the Eustachian tube.

It consists of a mucous membrane stretched over loose filamentous tissue inclosed by three muscles, the superior, inferior, and middle constrictor, and attached to the cuneiform process, the cervical vertebrae, and the lateral regions of the neck, by filamentous tissue.

By the superior laryngeal, the pharyngeal, the thyroid, the lingual, and palatine arteries, it receives blood, which is returned by a still greater number of veins to the external and internal jugular trunks. The nerves of the pharynx come from the glossopharyngeal, the hypoglossal, the pneumogastric, and the great sympathetic.

The oesophagus (gula) is a cylindrical musculo-membranous tube, communicating above with the pharynx, and below with the stomach. Placed above between the cervical vertebrae behind and the windpipe before, at the lower end of the larynx it inclines to the left, returns to the median line at the sternum, bends again to the left at the bifurcation of the trachea, and continues on the left side of the line, passing the aperture of the diaphragm, near the ninth dorsal vertebra, to its junction with the stomach. With the vertebral column behind, at its first inclination it covers the longus colli in the chest, crosses the rena azygos above, and covers the thoracic duct in the middle, and the norta below. With the jugular veins and carotids on each side in the neck, below it has the trachea on the right, and the recurrent nerve and common carotid on the left; and in the chest it has the aorta on the left and behind. (Plate XXIX, fig. 2, c.)

Lined on the inside by a follicular mucous membrane which assumes longitudinal folds (plica), the oesophagus consists of two ranges of muscular fibres, the one transverse, the other longitudinal. The first are most distinct at the pharyngeal end. The second form a manifest thick layer through the whole extent of the tube. Externally is a quantity of filamentous tissue, connecting the tube to that of the mediastinum and adjoining parts.

The oesophagus is supplied with blood from the inferior thyroid, thymic, laryngeal, pharyngeal; the aorta by proper oesophageal arteries, the superior intercostals and bronchials, the pericardial, mediastinal, diaphragmatics, and even the coronary of the stomach. The blood is returned by veins equally numerous. The oesophageal nerves proceed from three different sources. Above, it receives filaments from the glosso-pharyngeal and pneumogastric, in the middle from the latter, and below from the pneumogastric and the great sympathetic.

The stomach (ventriculus) is a large pyriform musculo-membranous sac, incurvated on itself (Plate XXIX, fig. 2, mac. and Plate XXXVI, fig. 4), situate in the epigastric and left hypochondriac regions, communicating above with the oesophagus, and below with the duodenum. Bounded above by the diaphragm, and the liver, which covers it, it has the spleen attached to its left great extremity, the transverse arch of the colon to the inferior large arch; and its posterior surface corresponds to the duodenum, pancreas, mesocolon, and large abdominal vessels.

The pyriform sac of the stomach is distinguished into a large end or sac (fundus), and a small extremity named the pyloric; while a particular incurvation of its direction gives it a large inferior arch (arcus major), and a small superior arch (arcus minor). At the left extremity of the latter is the cardia, the orifice by which the oesophagus enters the stomach (ostium oesophagium); and from this round the fundus is the large arch. A vertical plane drawn from the cardia divides the stomach into two portions,—the cardiac (fundus, secus eceus), and pyloric, terminating in an annular contracted opening, about an inch broad (pylorus, ostium duodenale sive pyloricum).

Between the two arches is the superior-anterior surface, covered partly by the left lobe of the liver, partly by the left rectus and hypochondre, and the inferior-posterior surface behind.

The stomach consists of peritoneum externally, mucous membrane internally, and an intermediate muscular layer with filamentous tissue.

The peritoneal covering is arranged in a peculiar manner. The anterior fold, meeting the posterior at the small arch, joins it, and forms a membranous production (omentum gastro-hepaticum), connecting the organ to the inferior surface of the liver, where they again separate to invest the upper and lower divisions of that organ. These folds, meeting in like manner along the large arch, where they form similar duplicatures, are again separated to in- close the spleen at the large end, and the colon along the lower division. In the triangular spaces formed by these duplicatures the gastric blood-vessels are lodged.

The mucous membrane, void of epidermis, is covered with minute piles (cilli) from the cardiac, where they commence at the fringed termination of the oesophageal epidermis, to the pyloric, where they are continuous with those of the duodenum. It is further puckered into wrinkles (rugae) or folds (plicae), intersecting each other irregularly, and inclosing irregular quadrilateral spaces,—an effect produced by the contraction of the muscular coat, and connected with the great extent of the gastric villous membrane. In this also are contained follicular glands, especially at the pyloric end and along the two curvatures.

The muscular coat consists of two ranges of fibres, one longitudinal, following the great diameter from the cardia to the pyloric end; the other circular internal, inclosing the circumference of the organ, and most distinct when the organ is empty. On the latter depends the contracted incursion of the stomach between the cardiac and pyloric divisions. (Plate XXXVI. fig. 4.) Besides these, there are on the left side of the cardia muscular slips expanded on the two surfaces.

The stomach derives its blood from the coeliac artery, the branches of which are arranged in a peculiar and beautiful manner. The coeliac divides into three vessels; one gastric proper, the coronary; one common to it and the liver, the gastro-hepatic; and one common to it and the spleen, the gastro-splenic. The first, the coronary, is distributed to the cardiac end, and, lodged in the peritoneal fold of the small arch, proceeds towards the pylorus, distributing branches before and behind. The second, after sending a large vessel to the liver, the hepatic, sends a small one (arteria pylorica), from the pyloric end, towards the gastric, by the superior peritoneal fold, to meet the terminal branches of the coronary; and a large one (gastro-epiploica dextra), by that of the large curvature, to meet the terminal branches of the left gastro-epiploic. The third or spleno-gastric artery, after transmitting a large vessel to the spleen, and various small vessels (ansa brevis) to the large fundus, sends a large vessel (gastro-epiploica sinistra), in the peritoneal fold of the large arch, to inclose with the terminal branches of the right gastro-epiploic. The stomach is in this manner embraced, as it were, by arterial canals above and below. It is further remarkable, that while only one proper gastric artery, of inconsiderable size and limited distribution, proceeds from the coeliac trunk, the gastro-hepatic and gastro-splenic, each not much less than the coeliac itself, send their largest branches to the stomach, and proceeding from opposite ends of that organ, inclose it, meeting by inoculation in the middle of its great and small curvatures. From the capillaries at the fundus, chiefly the ansa brevis, the gastric fluid appears to be secreted. The blood, returned by corresponding veins, is poured into the portal.

The stomach receives nerves from the pneumogastric and the great sympathetic. In the stomach the alimentary mass is converted into the pulp named chyme.

The duodenum (centriculus succenturiatus), about twelve inches long in the human subject, is distinguished by being the most fixed part of the tube in situation. Placed on the vertebral column, and on each side in the cavity of the mesocolon, behind the stomach, and concealed by that organ, it is bounded above by the liver and gall-bladder, below by the pancreas and lower part of the mesocolon, and maintains the communication with the pyloric end of the stomach and the ileum. The duodenum is divided by two curvatures into three portions. The first, which is covered by peritoneum, extending from the pylorus to the site of the neck of the gall-bladder, horizontally backwards and a little to the right, descends about two inches almost perpendicularly. With this the second portion, forming an angle, ascends obliquely to the left, and terminates opposite the third lumbar vertebra. The third, forming an angle rather more than right, extends about two or three inches, and terminates at the peritoneal ring, about one inch on the left of the spine, where the ileum commences. The aperture of the common biliary duct, inclosed in a nipple-like process, and the pancreatic, are in the first portion. These curvatures are firmly connected by filamentous tissue; and the bowel retains them even after removal from the body.

The duodenum, void of peritoneal covering, consists externally of cellular tissue, inclosing a range of circular muscular fibres, and lined by villo-mucous membrane, arranged in numerous folds, or valvulae conniventes. The duodenal arteries are derived chiefly from the gastro-hepatic, and are very generally pyloric twigs. This membrane is provided with follicles, first well described by Brunner.

In the duodenum, by admixture of the biliary and pancreatic fluids with the chyme, the latter is prepared for the separation of chyle, which, though more proper to the ileum, is begun nevertheless in this bowel. The comparative immobility of the bowel is requisite, both in consequence of the admixture now mentioned, and also of the fixed situation of the two glands by which the fluids are supplied.

The ileum (intestines) or small intestine (intestinum tenue), the longest part of the intestinal tube, extending generally from 28 to 30 feet, commences at the annular process above mentioned, and extends to the head of the colon, in which it opens in the right iliac region. It consists of a cylindrical musculo-membranous tube, surrounded by peritoneum, the two folds of which, meeting behind, attach it for the space of three or four inches to the vertebral column, and are again reflected laterally, as described in the first book of this treatise. This attaching membrane is named the mesentery. The great length of the tube, with the small extent of the mesentery, causes it to hang suspended in numerous turns or convolutions. By the ancients this intestine was distinguished into two parts, jejenum or the empty, and the ileum proper; and Winslow idly undertook to fix the limits of this division by referring the two upper thirds to the former, and the two lower to the latter. This distinction, however, for which there is no anatomical foundation, must be rejected as at once arbitrary and useless.

The muscular tunic consists of circular fibres entirely.

The villo-mucous membrane presents numerous valvulae conniventes, which increase its surface to at least double that of its proper area. These duplicatures are most numerous in the upper part of the tube, and diminish as they descend.

The mucous surface of the ileum is peculiar in presenting the piles or villosities in their most perfect form. When a portion of ileum is inverted, inflated, and immersed in pure water, an infinite number of minute processes are seen waving amidst the fluid; but a powerful glass does not enable the observer to determine whether they are round or flat, solid or hollow, obtuse or pointed. Of their shape and structure various accounts are given.

They were first represented, in 1721, by Helvetius, as cylindrical prominences in quadrupeds, but conical in the human subject. According to the microscopical observations of Lieberkühn, each villus receives a minute lacteal tube, arterial branches, a vein, and a nerve; and in each the lacteal is expanded into a minute sac or bladder (ampullula, vesicula) like an egg, in the apex of which may be seen by the microscope a minute opening. On this sac the arterial branches are ramified to great delicacy, and terminate in minute veins, which then unite into one trunk; while its inner surface he represents as spongy and cellular. The space between the villi, which do not touch each other, he further represents to be occupied by the open orifices of follicles, so numerous that he counted eighty of them where were eighteen villi; and both, he asserts, are covered by a thin but tenacious membrane similar to epidermis.

Hewson, while he admits in each villus the ramification of minute arteries and veins, denies the saccular expansion, and infers that the lacteals are ramified in the same manner as the blood-vessels, and that the whole constitute a broad flat body, the spongy appearance of which he ascribes to the mutual ramification of the latter. With this in general Cruikshank agrees; while Sheldon, who found the villi not only round and cylindrical as Hewson, but bulbous as Lieberkühn, and even sabre-shaped, rather confirms the statements of that anatomist. Mascagni and Soemmering, agreeing in the general fact of vascular and lacteal structure, seem to represent the shape of the villus as that of a mushroom, consisting of a stalk and a pileus.

Some of these discordant statements Hedwig attempts with equal ingenuity and industry to reconcile. The differences in shape he refers to differences in the animals examined; and in one class finds them cylindrical (e.g., in man and the horse); in another conical (the dog); in a third club-shaped (the pheasant); and in a fourth pointed or pyramidal (e.g., the mouse). The interior structure he also represents as spongy in all the animals which he examined; and invariably also he found at the apex the orifice of the duct, which, after the example of Lieberkühn, he conceives constitutes the ampulla.

These conclusions are not exactly confirmed by the researches of Rudolphi, who examined the villi in man and a considerable number of animals. This anatomist never found the orifice seen by Hedwig, notwithstanding every care taken to distinguish it. He maintains that the villi are not alike in all parts of the intestinal canal of the same animal, as represented by Hedwig, but may be cylindrical in one part, club-shaped in another, and acuminate in a third. Admitting their vascular structure, which he thinks may be demonstrated, he regards the ampullar expansion as doubtful, and denies its cellular arrangement.

About the same time Bleuland, who had previously examined the intestinal mucous membrane, after successful injection of its capillaries, undertook to revive the leading circumstances of the description of Lieberkühn. By examining microscopically well-injected portions of intestine, he shows that the villi are composed of a system of very minute arterial and venous capillaries, inclosing a lacteal, which constitutes the ampulla, and in the interior of which a certain order of these capillaries terminates. He also revives the statement of the absorbing orifice at the extremity of each villus.

According to the observations of Beclard, the intestinal villi appear neither conical, nor cylindrical, nor tubular, nor expanded at top, as described by several authors, but in the shape of leaflets or minute plates, so closely set that they form an abundant tufted pile. Their shape varies according to the manner in which they are examined, and according to the part. Those of the pyloric half of the stomach and duodenum are broader than long, and form minute plates; those of the jejunum are long and narrow, constituting piles; at the end of the ileum they become laminar, and in the colon are scarcely prominent. They are semitranslucent; their surface is smooth; and neither openings at their surface, in their cavity, or in their interior, nor vascular structure can be recognised.

The villo-mucous membrane of the ileum is provided with mucous follicles of two orders, the glandula solitaria and the glandula agminata; the former, like granules, disseminated over the attached surface of the mucous membrane; the latter clustered in bodies at the anterior exterior part. They partake of the general characters of follicular structure.

The ileum is liberally supplied with blood by the superior mesenteric artery; the arrangement and distribution of which may be understood from fig. 4, Plate XXIX.

The nerves are derived from the solar plexus.

The colon, or large intestine (intestinum crassum), beginning in the right iliac region, extends round the folds of the abdominal cavity, inclosing the ileum, to the left iliac and pelvic, where it terminates in the rectum. Its length is from six to seven feet. The beginning (cecum) is a round obtuse bowel, with a minute tubular process, varying in length, named the vermiform. The lower end of the ileum is inserted into the beginning of the colon laterally; and to the part below the insertion the name of cecum or blind gut is restricted. From the cecum the colon descends to the right hypochondre (colon dextrum), where it is connected at the hepatic flexure to the liver by the hepato-colic ligament, two folds of peritoneum, with intermediate filamentous tissue; between the right or hepatic flexure and the left or splenic it is distinguished as the transverse arch (colon transversum), attached to the large arch of the stomach by the gastro-colic margin of the omentum; an angular bend in the left hypochondre forms the splenic flexure; and, finally, after making a long sinuous alternating bend in the left iliac and pelvic regions, named the sigmoid flexure, it terminates in a portion comparatively straight (rectum), and following only the antero-posterior incursion of the inner surface of the sacrum, on which it is placed.

The colon is about two inches in diameter at an average.

The appearance of this intestine is intimately connected with its structure. Inclosed in peritoneum, by the posterior junction of which it is connected to the adjoining organs, it consists of a layer of circular fibres, intersected by three bands of longitudinal fibres. Both are asserted to be muscular; but perhaps the latter are more of the nature of aponeurosis, to give support and resistance to the action of the former. Whatever be their nature, however, they give the colon the appearance of being divided into transverse cells, separated by superficial partitions.

The mucous membrane of the colon possesses the villous character in the cecum and right part; but loses it towards the lower part of the intestine. It is formed into large transverse folds or duplicatures, which separate the internal cells or compartments of the bowel.

At the insertion of the ileum into the colon the mucous membrane of each is prolonged with the submucous tissue, and they mutually meet in two crescentic processes, valve, one superior, small (plica superior, labium superius), the other inferior, large (plica inferior, labium inferius), and approaching, by its greater prolongation, the paraboloid shape. The ideal side of both folds is concave, the cecal or colic convex; and between their free margins, which are rounded, is an intermediate fissure, maintaining the communication between the two intestines. This arrangement, which is named the ileo-cecal valve (valvula Bauhinii, from its supposed discoverer), is supposed to allow the transit of alimentary and excremental matter from the ileum to the colon, but not in the converse direction.

The organization of the rectum is the same as that of the colon generally; but it is uncovered by peritoneum behind. Its lower extremity is surrounded by two circular ranges of muscular fibres, named the internal and ex- ternal sphincters. The lower fibres of the levator ani are inserted into its sides.

The cæcum and right and transverse portions of the colon are supplied with blood from the superior mesenteric, by means of the colic arteries. The left iliac or sigmoid flexure receives vessels from the inferior mesenteric. The splenic part is supplied by vessels derived from the great anastomotic communication between the superior and inferior mesenterics. (Plate XXIX. fig. 4.) The rectum is copiously supplied with blood from three different sources. The first is the termination of the inferior mesenteric, which is contained between the folds of the mesorectum, under the name of superior hemorrhoidal. The second is the middle hemorrhoidal, or proper artery, derived from the hypogastric or posterior iliac. The third is the internal pudic, the lower or perineal branch of which supplies the sphincter with several branches on each side, distinguished by the name of inferior hemorrhoidal arteries.

The nerves are derived partly from the hypogastric plexus, partly from the sacral branches.

The rectum, like the pharynx, placed between the two classes of organs, entrophic and animal, belongs in some degree to both. As the termination of the alimentary canal, it belongs to the former; but by its sphincters and levator it pertains to the latter.

The appendages of the alimentary canal are two glands, the liver and pancreas, and a cellulo-vascular organ, the spleen.

The liver (hepar, jecur) is a large glandular organ, weighing from two to three pounds, situate in the right hypochondriac and epigastric regions, with the diaphragm above, and the hepatic flexure of the colon and the stomach below. It has a convex upper surface, a concave lower one, a posterior obtuse margin attached to the diaphragm by cellular tissue, and an anterior inferior acute one which is free. The lower surface is distinguished into right and left lobes by a middle pit (sulcus umbilicalis, v. horizontalis), in which the round ligament, the residue of the umbilical vein, is contained, and which is occasionally a canal by an arch of hepatic substance. The inferior surface of the left lobe is divided into anterior and posterior parts by a transverse furrow (sulcus transversus, fossa transversa), in which the trunk of the hepatic arteries, and the portal vein, and the hepatic ends of the biliary ducts, are contained. The margins of this furrow, which are elevated in the lower animals, were named gates by the ancients (στοιχεῖα, portae), from an erroneous theory. The posterior, which is most prominent, is distinguished by the name of small lobe of Spigelius (lobulus Spigelii). The other distinctions of this surface into lobulus quadratus and lobulus caudatus are immaterial. Between the anterior portal eminence and the umbilical fossa is an oval depression (fovea cystica), containing the gall bladder.

The liver is invested by peritoneum, the folds of which connect it to the neighbouring organs, and retain it in its place. Of these, the most important are the broad and coronary above, the lower or falciform below, and the gastro-hepatic duplicature between the liver and stomach. This forms the investment named capsula of Glisson, in which the portal veins are included.

The structure of the liver is glandular. Two classes of and organ-vessels and a system of tubes are distributed in it; one ramifying into branches and minute tubes, the hepatic artery and portal vein; another, the hepatic veins, converging to a trunk, the vena cava hepatica; the third, the peri biliares, converging into ducts terminating in the hepatic duct. From the researches of numerous anatomists, it appears that the hepatic artery, which is derived from the celiac, and the portal vein, formed from the veins of the stomach, intestines, spleen, and pancreas, terminate in minute vessels mutually communicating. It appears further, that these capillaries communicate with those of the hepatic veins, and even the origins of the biliary pores; and Soemmerring especially infers, that every hepatic acinus consists of hepatic artery, portal vein, hepatic vein, bile-pore, and lymphatic. From this, however, it does not altogether result that bile is secreted from the hepatic arterial blood. Each acinus may require a minute artery for nutrition, a portal venule for furnishing the materials of secretion, a duct for receiving the secreted product, and a vein for returning the residual blood.

The hepatic duct unites at an angle with the cystic, and forming the common duct, terminates in the duodenum. The gall bladder, which is a pyriform bag, with the fundus below and before, and a neck above and behind, acts as a receptacle for the bile when it is not required in the duodenum. The fundus, placed between the concave surface of the liver above, and the convex one of the pyloric division of the stomach below, may be compressed by that part of the organ when distended, so as to expel the bile from its cavity.

The pancreas is a flat, oblong, glandular body, measuring from five to six inches in length, and weighing from three to five ounces, contained in the posterior epiploic cavity below the duodenum. It consists of lobules similar to those of the salivary glands. It has a proper artery, from which the pancreatic fluid, very similar to the salivary, is secreted, and conveyed into a small duct. The residual blood is conveyed by a proper vein to the portal.

The spleen (lien) is an oblong hemispherical organ, of the spleen, a deep blue venous blood colour, varying in weight from 6 to 12 or 15 ounces, placed in the left hypochondriac, between the fundus of the stomach and the left side of the diaphragm, with a plane surface applied to the former, and a convex to the latter part. The spleen is covered by peritoneum, which, doubling before, forms along the middle of the organ a gastro-splenic omentum, by which it is attached to the stomach. It is generally connected to the colon by a short peritoneal slip.

The intimate structure of the spleen is peculiar. It consists of a number of minute communicating compartments, separated by septa, with white granules intermixed. These cells contain dark-coloured blood; and the organ is indeed more abundantly filled with this fluid than any other in the body. These cells appear to be of the nature of erectile vessels. The splenic artery is very large in proportion to the organ, and apparently communicates by minute terminations with veins, in which the blood is occasionally accumulated.

The principal use of the spleen appears to be, that it serves as a receptacle for a large quantity of blood, which accumulates in the splenic vessels, or flows into those of the stomach, as the latter organ requires. When the stomach is empty, it shrinks; and its blood-vessels, folded on themselves, neither require nor transmit so much of this fluid as they do when the organ is distended. In the latter case the vessels are stretched, their canals are rectified, and the blood flows freely through them. At this period the additional supply seems chiefly to be derived from the spleen. The splenic vessels also appear to contribute chiefly to the secretion of the gastric fluid, which is most abundant at the fundus of the organ.

SECT. II.—THE CYLOPHOROUS VESSELS.

On the lacteals or intestinal lymphatics it is superfluous to add anything to what is stated in Book I.

These vessels arise from the villous surface of the ileum, and proceeding between the folds of the mesentery, unite at the vertebral margin of that membranous duplicature, somewhere between the third lumbar vertebra and the aor- Special tic opening of the diaphragm. Here they terminate in a jointed irregular tube situate behind the aorta, and which, passing through the aortic opening of the diaphragm, proceeds through the chest between the artery and vena cava, as high as the sixth, fifth, or fourth dorsal vertebra. Here it inclines to the left, and, passing behind the aortic arch and the left subclavian artery, winds to the left of the latter vessel, and, before the longus colli, ascends as high as the seventh or sixth cervical vertebra, where it terminates in the angle between the internal jugular and subclavian veins, in the trunk of these vessels. This is the thoracic duct. A similar vessel, though smaller, is found on the right side.

CHAP. II.—THE HEMATOPHIC ORGANS.

The organs of the hematrophic or circulating function consist of the heart as a central propelling agent, and of arteries and veins as distributing and reductent channels. The hematrophic organs may be distinguished into three orders; first, those of the general or nutritive circulating system; secondly, those of the aerating circulating system; and, thirdly, those of the secreting system. Of these the heart is the central agent; but in the mammalia and man it consists of two divisions, one pertaining to the general arterial, the other to the pulmonary or aerating system.

SECT. I.—THE ORGANS OF NUTRITIVE CIRCULATION.

§ 1. THE HEART AND HEART-PURSE.

The heart is a conical muscular organ, containing four communicating chambers, inclosed in a membranous sac, and situated in the anterior middle region of the thorax. The inclosing sac, named heart-purse, or capsule of the heart (pericardium), consists of two portions or layers, an outer or proper capsular, and an inner or lining division. The outer or proper capsular part of the pericardium possesses the characters of a fibrous membrane, of some density and considerable strength. When washed, its colour is gray or grayish-white, and it appears to consist of minute fibrous threads, arranged without definite order. These fibres are most distinct at its lower margin, where it is connected to the circumference of the tendinous part of the diaphragm. In the young subject it is generally thin and translucent; in adult age or advanced life it is thicker and more opaque. This part of the pericardium is a mere investing membrance, which bounds the region containing the heart, but which extends no further. It embraces the origins of the large vessels above, adheres to the margins of the tendinous centre below, and is on each side connected with the pleura.

The inner surface of the pericardium has the appearance of a transparent or serous membrane, through which the fibres of the outer or capsular part may be seen, and which has the usual glistening aspect of such membranes. It is difficult, however, to insulate it from the outer layer, unless by boiling, when it may be peeled off in minute shreds. Like the transparent membranes, this inner layer has neither beginning nor end, neither origin nor termination. After lining the inner surface of the proper capsule, it may be traced from the angle at which this capsule adheres to the large arteries and veins, over the auricles, and finally, over the outer surface of the ventricles to the apex of the heart.

In this course it preserves the characters of a thin transparent membrane, with a free surface, smooth, glistering, and moistened by a watery fluid; and an attached one, adhering on the one hand to the inner surface of the capsule, and on the other to the outer surface of the heart by means of fine filamentous tissue.

Injection shows that the pericardium consists chiefly of minute arteries and veins. The former are derived from the thymic, phrenic, bronchial, oesophageal, and coronaries of the heart. The substance of the capsular part is probably a modification of the white fibrous system. Nerves have not been traced to any part of this membrane; nor is it ascertained that it contains lymphatics.

Of a general conical shape, the heart (cor) is situate obliquely beneath and behind the sternum, with the base (basis) above and towards the right, and the tip (apex) pointing downwards, forwards, and towards the left. The axis of the cardiac cone lies at once obliquely from right to left and from behind forwards. (Plate XXXI.) The surface may be distinguished into two parts,—the anterior convex, appearing in the space between the right margin of the sternum and the sinuosity of the left lung; the posterior plane, resting chiefly on the oblique surface of the diaphragmatic tendinous centre. These two surfaces are united by a sharp anterior-inferior margin (margo acutus), and an obtuse posterior-superior one (margo obtusus). It generally corresponds in size with the fist of the individual; its average weight in the adult is about ten ounces; and its length from the middle of the base to the tip is about five inches.

The base of the heart is circular, flattened behind, and presents an oblique groove, which indicates the limits between the auricles and the ventricles.

Each auricle is of a tetrahedral shape, and is distinguished into the basilar or membranous part (sinus venosus), and the tip or proper auricle (auricula), a pyramidal angular process, the structure of which is muscular. The right auricle is the largest, the left smaller.

The ventricles constitute the great part of the cardiac cone. Their anterior and posterior surfaces present each a longitudinal depression (sulcus longitudinalis superior et inferior), proceeding from the base to the tip, containing the anterior and posterior coronary vessels, and indicating the situation of the fleshy partition (septum ventricularum) common to both ventricles.

The interior of the right auricle behind presents above the opening of the superior cava (ostium venosum superius), below that of the inferior cava (ostium venosum inferius), larger, directed obliquely inward, with an intermediate eminence (tuberculum Loucari), denominated after Lower, and the Eustachian valve below (vol.ii.794). Below and anteriorly is the opening into the ventricle, bounded by a round margin (ostium inferius); above is the tip presenting muscular bands (musculi pectinati); and within is the partition common to both auricles (septum auricularum), with an oval depression (fossa ovalis), the residue of the foramen ovale, occasionally bounded before by a crescentic slip of membrane.

The right ventricle (ventriculus dexter red pulmonalis) is trilateral pyramidal in shape, with its base above corresponding to the inferior auricular aperture, its apex to that of the heart, the anterior-external wall corresponding with the anterior convex surface of the heart, and the posterior-internal with the common partition (septum cordis). It has two apertures—a right superior, communicating with the auricle; and a left superior, communicating with the pulmonary artery.

To the margin of the superior right aperture (ostium auriculo-ventriculare dextrum), which is round and thick, are attached several membranous triangular folds (laciniæ), with two, or occasionally three apices, to which are fixed tendinous chords (chordæ tendineæ), with their opposite extremities terminating in muscular cylinders (muscoli papillares, m. teretes), connected with the fleshy walls of the ventricle. This membranous fold, though often composed of two triangular slips only, is denominated the three-pointed or tricuspid valve (valvula triglochin, v. tricuspidalis). Its apices hang into the ventricular cavity, and are prevented by the tendinous chords and their muscular bands from being forced back into the auricle.

The left superior aperture (ostium arteriae pulmonalis), corresponding to the beginning of the pulmonary artery which is attached to it, is placed behind the inner slip of the tricuspid valve, by which also it is covered. The inner margin of the pulmonary artery presents three crescentic or semilunar slips, named the sigmoid valves (valvula sigmoides), with their convex surface towards the ventricle, and the concave one towards the artery, and minute bodies at the middle (noduli Morgagnii), corresponding to the axis of the artery.

The interior of the left or posterior auricle presents on the right the two openings of the right pulmonary veins, on the left those of the left pulmonary veins, occasionally uniting in a single aperture, to the right and anteriorly the left surface of the septum, bounded before by a small semilunar slip, and below the aperture into the left or aortic ventricle.

The left ventricle has the shape of an obtuse cone, with its base above and behind, and its rounded apex behind and to the left. It is rather larger than the right. The basis has two apertures, a large posterior one, communicating with the auricle (ostium auriculo-ventriculare sinistrum); and a smaller anterior, opening into the aorta (ostium aorticum). To the ventricular margin of the former is attached an irregular membranous slip, not dissimilar to that of the right auriculo-ventricular opening; but always terminating in two apices, to which tendinous chords, connected with tapering muscular bands, are also attached. This has been denominated the bicuspid or mitral valve (valvula mitralis). Like the tricuspid, its apices hang into the ventricle, and are prevented from being retracted into the auricle by the tendinous chords and papillary muscles.

The aortic aperture, anterior and smaller, corresponds with the commencement of the aorta. Like the pulmonary aperture of the right auricle, it presents three semilunar valves, with the convex surface to the ventricle and the concave to the artery, and with central granules (corpuscula Arantii). These valves are occasionally distinguished into anterior, posterior, and inferior or lateral, according to their relation to the plane of the body. In their aortic side are generally small hollows, chiefly occasioned by distension of the aorta, named aortic sinuses.

The heart consists chiefly of muscular fibres, closely united by filamentous tissue, covered externally by the reflected or cardiac portion of the pericardium, and internally by a proper membrane.

Each auricle consists of two parts,—a membranous-muscular, arranged in the stratified mode (fascia), distinguished as the sinus; and a fasciculo-muscular, distinguished as the tip of the auricle, arranged in short parallel bundles (funes). The muscular walls of the left ventricle are more than double the thickness of the right; and while those of the latter collapse on division, those of the former retain their original disposition. The fleshy pillars of the interior of the right are small and slender compared with those of the left, which are thick and strong.

The arrangement of the muscular fibres of the heart, which has been studied by Senac, Wolff, Duncan, and Gerdy, is peculiar. Though mutually interlacing, like all the muscles of the entrophic order, the external are arranged in layers (strata), while the internal affect the fasciculated form. At the base they are incurved round the basilar border, and wind obliquely towards the apex; but as they approach the latter region, more especially in the septum, they observe the longitudinal direction. The insertion of Soemmering, that they are distinguished as being connected without filamentous tissue, is inaccurate.

The adipose tissue at the surface, and towards the base and apex of the heart, appears to be useful in facilitating motion in an organ in incessant action, and forms a soft cushion for the cardiac arteries.

The inner membrane of the heart is thin and transparent. In the right auricle and ventricle, where it is continuous on the one hand with the inner venous membrane, on the other with the inner membrane of the pulmonary artery, it is evidently different from that in the left cavities. It is thinner, and more delicate and transparent. Covering every recess, it is doubled to form the different valvular productions. By Bichat it is believed to be identical with the inner venous membrane; but this is mere supposition. In the left cavities the inner membrane is thicker and more opaque than the right; and its valvular duplicatures, which are much thicker, approach to the fibro-cartilaginous character. This is particularly the case in the aortic sigmoid valves, which often in the healthy adult are firm and elastic, not unlike the palpebral fibro-cartilages. The supposition of Bichat, that it is identical with the inner arterial membrane, with which it is continuous, is, in regard to the ventricle, not improbable.

The heart is supplied with blood from the aorta by means of the right anterior or inferior, and the left superior or posterior coronary or cardiac arteries (arteriae cardiae), both issuing from the aortic sinus immediately above the anterior and lateral sigmoid valves. The right or anterior coronary artery, lodged in the superior furrow, after sending several large branches to the septum and left ventricle, inosculates at the apex with a large branch of the left or posterior coronary. The latter, which is the largest of the two, after winding round the base of the heart towards the right, is recurved at the thin margin to the posterior surface, where it runs in the posterior furrow, and is divided into two considerable branches, the larger of which is distributed to the apex; while the smaller, running transversely between the left auricle and ventricle, winds round to the obtuse border, and terminates at the apex, where all the three vessels inosculate freely. The blood is returned by corresponding veins to the coronary, which terminate by one aperture in the right auricle. Its nerves are derived from the pneumogastric and sympathetic.

The four chambers of the heart (atria, atriola) are distinguished into pairs,—a right auricle and ventricle communicating mutually and with the pulmonary artery, and a left auricle and ventricle communicating with the aorta. The auricles, separated by the common septum, do not communicate in the natural state; and though in many hearts an oblique opening exists at the anterior margin of the oval depression passing into the left, the crescentic membranous slip by which it is covered prevents the blood of the right auricle from communicating with that of the left. The ventricles are separated also by a thick, fleshy, common partition, through which there is no direct communication, though it was a favourite subject of inquiry before the time of Harvey, to discover communicating apertures.

The capacity of these chambers varies. The right auricle is always more capacious than the left. The two cardiac ventricles are, as near as may be, of equal capacity; and chambers. the discordant results obtained on this point by numerous inquirers show merely that any variation is accidental or dependent on the state of the organ during the close of life. The blood found in the right ventricle after death varies from 1½ ounce to 3 ounces. The capacity of the left, which is generally empty, is estimated by Meckel to vary from 8 to 20 drachms. The blood contained in the right chambers is modena- coloured or venous; that of the left chambers is scarlet- red or arterial. The former is derived from the vena cavae, which open into the right auricle; the latter from the pulmonary veins, which open into the left. The di- rection in which the blood flows on both sides is from the venous apertures into the auricles, thence to the ventricles, and thence to the respective arteries. The venous blood, on reaching the auricle, distends it, and impels its muscles to contraction; and the cavity thus diminished expels the blood in the only direction in which it can proceed,—by the auriculo-ventricular aperture into the ventricle. This chamber being distended, its muscular walls all round, especially at the base, contract and diminish its cavity, when the blood, extruded, quits the ventricle in the only direction in which it can, viz. by the aperture of the pul- monary artery. The blood from the pulmonary veins fol- lows the same course in the chambers of the left side. The blood of the ventricles is prevented from returning into the auricles partly by the tricuspid and mitral valves, but chiefly by the annular contraction of the auriculo-ven- tricular apertures, which are drawn from the margins to- wards the septum; while the latter is shortened, and the apex is made to approach the base.

§ 2. THE ARTERIES AND VEINS.

Connected with each ventricle is a large tube, in which the blood flows from the trunk to the branches. The pulmonary artery, the first of these, divaricates into a right and left branch, subdivided and distributed respec- tively to the right and left lung.

The aorta, which is the second, is the large artery which distributes the blood after aeration in the lungs to the system at large.

The aorta, rising from the left ventricle, after giving off the cardiac arteries, makes an antero-posterior incurva- tion with the convexity upwards, denominated the arch or curvature (arcus aortae). (Plate XXXI. A, A.) From the upper side of this arch arise three large vessels, the innominate or subclavio-carotid, the common trunk of the right subclavian and carotid arteries (1), the left carotid (1), and the left subclavian. The aortic trunk, after this curvature, proceeds downward on the left margin of the dorsal vertebra, giving cesophageal, bronchial, and superior intercostal arteries, thymic, pericardial, and in- ferior intercostal arteries successively. From the level of this arch to the parabolic opening of the diaphragm at the tenth dorsal vertebra, it is distinguished by the name of thoracic aorta; and below this, to the fourth lumbar verte- bra, it is the abdominal aorta. At its transit through the parabolic aperture it sends off the diaphragmatic arteries.

The vessels issuing from the abdominal aorta may be dis- tinguished into two orders, those which issue from its sides in pairs, and those which issue from its anterior surface sing- ly only. The former consists of the capsular, distributed to the renal capsules; the renal or emunctive, to the kidneys; the spermatic, to the testes; and the lumbar, to the lumbar muscles, and that region generally. The latter are three in number only, the celiac, superior mesenteric, and inferior mesenteric. Opposite the fifth lumbar vertebra, or the fibro- cartilage uniting the fourth and fifth, the aorta terminates by divaricating into two large lateral trunks, the common or primary iliacs (iliae communes); while from its middle be- hind proceeds a small azygos artery, distinguished as the sacro-median, along the median line of the sacrum. In this course the aorta is placed in the posterior angle of the thoracic and abdominal serous membranes, and, inclosed by the anterior vertebral filamentous tissue, sends from its posterior surface numerous arteries to the vertebral column and spinal chord.

VOL. III. In general the denominations of these arteries indicate the parts to which they are distributed. In the ultimate distribution of the arterial system, however, there is great variety; and it is often impossible to determine the exact origin, course, and distribution of the smaller terminations. The trunks alone are constant in position. In distribution, the following general rules are observed:—1st, The arterial trunks send small lateral branches to the parts between which they run. 2ndly, The majority of individual organs are supplied, not by one proper vessel, but either by one principal artery and two or more subordinate ones, or by several subordinate ones. 3rdly, A trunk, after giving off several lateral branches, may either terminate in one vessel, which is ultimately distributed to the organs to which it is destined; or it may divaricate into several, none of which may be considerable enough in size, or direct enough in course, to be regarded as the proper terminal vessel. Thus it is often difficult to determine whether the temporal artery or the internal maxillary is the continuation of the external carotid, which of the palmo-digital arteries is the continuation of the radial, whether the anterior or the posterior tibial artery is the continuation of the popliteal, and whether the dorsal of the foot is the termination of the former. 4thly, In the terminal vessels, where inoculation is frequent, it is impossible to determine whether an artery arises from one trunk or another. Thus in the arterial arches of the hand and foot, in which the digital vessels issue from the convexity of the arch, it is impossible to say whether these arteries arise from the radial or the ulnar in the one case, or the anterior or the posterior tibial in the other.

The arteries are accompanied by veins, which in general correspond, for the purpose of conveying the residual blood, after distribution, to the right chambers of the heart, to be transmitted by the pulmonary artery to the lungs for renovation. The veins of the head, chest, and superior extremities, open into the superior cava; those of the lower part of the trunk, the pelvis and pelvic extremities, terminate in the inferior cava; the veins of the stomach, intestinal canal, spleen, and pancreas, terminate in the portal vein; and the regredient hepatic veins are united in one vessel, which terminates in the upper end of the inferior cava.

SECT. II.—THE ORGANS OF AERATING CIRCULATION, OR RESPIRATION.

The lungs are two soft, spongy, vascular bodies, contained in the cavity of the chest, one on each side, and imitating in shape the internal figure of that region. Each lung, resembling somewhat a cone, with one side truncated, and the base obliquely cut, is distinguished into a convex external surface, corresponding to the concave internal one of the thorax; a flat inner or mesial surface, corresponding to the mediastinum; a rounded obtuse apex, corresponding to that of the demithorax; and a concave base directed obliquely from the mesial plane to the hypochondres, corresponding to the convex surface of the diaphragm.

Each lung is distinguished into lobes (lobi) separated by fissures (incisurae). The right, which is the largest, consists in general of three lobes, the superior, middle, and lower; the left of two only, an upper and lower. The mesial margin of the left is distinguished from that of the right by a sinuous notch, indicating the situation of the heart (fovea cardiaca).

The intimate structure of these bodies, which has been the subject of much research, depends on the nature of the tubes which are distributed to them, and of which chiefly they consist. These are the bronchial or breathing tubes (bronchi), the continuations of the windpipe, and the branches of the pulmonary artery and veins.

The windpipe (trachea) is a cylindrical tube, about four or five inches long, extending from the cricoid cartilage, to which it is attached by a fibro-mucous membrane behind the sternum, to the level of the third dorsal vertebra, or the fibro-cartilage between it and the second. (Plate XXXI. r.) It consists of from 17 to 18 or 20 cartilaginous rings (annuli), truncated behind, united by a fibrous membrane without, continuous, but particularly firm in the interannular spaces, and along the whole posterior part of the canal. These fibres are white, firm, longitudinal, and closely set. Within is the mucous membrane, continued from the larynx to the bronchi, resting on filamentous tissue, in which are embedded the mucous follicles. By many, muscular fibres have been represented to exist between the rings; according to Soemmering transversely and longitudinally; and Reisseissien has recently maintained their reality at the posterior part of the tube. Their fibrous disposition is undeniable, but their muscular character may be doubted.

The windpipe, covered before by the thyroid gland, and corresponding to the sigmoid pit of the sternum, is attached to the oesophagus behind by filamentous tissue.

Opposite the third dorsal vertebra the trachea is bifurcated into two tubes named air-tubes (bronchi), which are directed obliquely to each lung with a mutual intermediate angle of about 35°. The right is about one fourth larger and one fifth longer than the left. Both are cylindrical, but divaricate at their lower end, where they sink into the substance of the lungs, into several smaller tubes (bronchiole), which again ramify and subdivide into tubes still smaller, and successively. The interbronchial angle is occupied by lymphatic glands, which are also arranged round the tubes.

The bronchi consist of cartilaginous rings, complete above, but parted into three annular segments between the middle and lower ends, united by whitish fibrous tissue, longitudinal externally, transverse within, and lined by mucous folliculated membrane. As they advance into the substance of the lungs, and are still more minutely divided, the cartilages diminish in size and firmness, and their place is supplied by fibrous tissue of transverse circular fibres, which at length also disappear, and mucous membrane alone is left.

These transverse annular fibres have been supposed by Haller, Soemmering, and recently Reisseissien, to be muscular. It is not improbable that they are so; but no positive proof of this fact has yet been adduced, and they appear rather to belong to the elastic fibrous system.

The larger bronchial tubes are accompanied each by an artery derived from the aorta or the subclavian, and following their ramifications into the pulmonic substance. The blood conveyed by these vessels is returned either to the vena azygos or the superior cava.

The pulmonic or final divisions of the bronchial tubes terminate in blind sacs covered by mucous membrane, and communicate with each other, forming an appearance of intersecting compartments, which have been distinguished by the name of air-cells (cellulae aereæ), or pulmonic vesicles (vesiculae pulmonis). They are represented as polygonal and irregular, and about one eighth or one tenth part of a line in diameter. (Haller and Soemmering.) On the whole, these air-cells appear to be merely the terminations of the bronchial tubes mutually communicating, lined by a very delicate mucous membrane.

The pulmonary artery, ramified and subdivided to a great degree of minuteness, communicates most freely with a number of vessels, which may be traced into trunks terminating in the pulmonary veins. This capillary system, enveloped in filamentous tissue, is distributed beneath the mucous membrane of the terminal bronchial tubes or communicating cells. The exterior surface of this filamentous tissue is covered by the pleura. From these facts it results that the lung consists of cartilaginous and fibrous tubes mutually intersecting, and the capillary communications of the pulmonary artery and veins, involved in filamentous tissue, lined on one side by mucous membrane, covered on the other by transparent serous membranes. The air-cells, lined by mucous membrane, have no communication with those of the filamentous tissue, as some have absurdly imagined. Except this filamentous tissue, the lung has no proper substance or parenchyma; and its structure is entirely filamento-vascular.

In the capillary vessels of the pulmonary artery and veins, the venous or modern blood, exposed to the influence of the inspired air through the thin bronchial membrane, parts with its dark, and gradually acquires a bright red tint. This may be styled the aerating or arterialized capillary system.

The lung, however, receives other vessels, the bronchials, by which its mucous aerating membrane and submucous tissue are nourished. Entering with the bronchial tubes between the folds of their pleura, these vessels are subdivided as they proceed, and at length form a minute network on the attached surface of the bronchial mucous membrane.

The lung derives its nerves from the eighth pair chiefly, and a few filaments from the great sympathetic. The lung is well supplied with lymphatics, both superficial and deep.

SECT. III.—THE ORGANS OF SECRETORY CIRCULATION, OR SECRETION.

Of the organs of secretory circulation, several, as the lacrymal gland, the salivary glands, the liver, and pancreas, have been already considered; and others, for example the testes, will fall under subsequent heads. This, however, is the proper place to notice the organs of the urinary secretion, which consist of two glands, the kidneys, and two excretory ducts, the ureters, terminating in a common receptacle, the bladder.

The kidneys (renes) are two glandular bodies situate in the posterior or lumbar part of the abdominal region, one on each side of the lumbar vertebrae, behind the peritoneum, and before the psoas muscle and part of the diaphragm, with the quadratus lumborum behind and laterally, and enveloped in a thick layer of adipose tissue.

The right kidney is below the liver, above the cecum, behind part of the duodenum, colon, and the right extremity of the pancreas. The left is bounded above by the spleen, by the transverse arch of the colon before, and it has the sigmoid flexure below. The right kidney is about two inches from the outer margin of the vena cava, and the left at about the same distance from the outer margin of the aorta.

The situation of the right kidney is generally lower than that of the left, so that part of its lower extremity is in the iliac fossa, while the lower extremity of the left is quite above the margin of the ilium.

Resembling in general shape the large French bean, named from it, each kidney may be described as an oblong body, convex externally and at both ends, and with a sinuosity at its inner margin, named the renal fissure (fossa renis), in which the vessels and excretory duct are contained. Each kidney is between four and five inches long, and two broad; and the weight of each varies from three to four ounces. The anterior surface, corresponding but not attached to the outer surface of the peritoneum, is convex, but becomes hollow at the inner margin, where it terminates in the renal fissure. The posterior surface, which is less convex, is separated from the internal aponeurosis of the transverse abdominal muscle, the diaphragm, and the psoas magnus, by a thick layer of adipose tissue.

The kidney consists of glandular structure, invested by a firm membrane, somewhat fibrous in appearance.

In the glandular structure the anatomist recognises the most distinct example of this form of tissue. It consists of two parts, a granular external, and a tubular internal. The former, which occupies the exterior of the kidney, is a homogeneous substance, of a yellow fawn colour, and consists of minute spherical or spheroidal granules (granula), aggregated together by filamentous tissue, and forming at their exterior calycoid or cup-like cavities, in which the round fundi of the tubular conoids are lodged. In these the capillary vessels of the kidney are ramified with great minuteness. The tubular part consists of very minute capillary tubes (tubuli uriniferi, tubuli Belliniiani), varying in length, united by filamentous tissue, and arranged in parallel juxtaposition, so as to form conoids with globular bases, which are lodged in the cup-like cavities of the granular portion, and rounded apices directed to the renal fissure. The number of these tubular cones varies from 10 or 12 to 18 or 20. Their apices form an equal number of nipple-like processes (papillae), covered by a thin membrane almost transparent, in which are numerous minute holes, apertures of the tubes of which the cones are composed. These apertures, however, are much less numerous than the tubes, several of which are united in one common orifice. The renal papillae thus constituted project into a series of conical cavities, formed within of the papillary membrane, without of fibrous strata and filamentous tissue. These cavities, which from their shape are denominated funnels (infundibula, calyces), uniting into three or four larger ones, terminate in a considerable membranous sac named the basin (pelvis) of the kidney.

These two parts of the kidney are distinguished not only in structure but in colour and consistence. While the granular part is fawn-coloured, and somewhat soft and flabby, the tubular is pink-red, fleshy and firm; and the boundary line is distinct. The tubular cones are separated from each other by partitions, which appear to be filamentous tissue.

There is no doubt that the granular is the secreting part of the gland; and the tubes are merely conduits of the urine, which indeed may be expressed from their apertures. It is important, however, to determine the mode in which the two portions communicate. The assertion of Ferrein and Eysenhardt, that the tubes are blind canals, is inaccurate in this respect, that the terminal tubes evidently communicate with others in the interior of the cones, which again are immediately connected with the granular part. It further appears, that in the granular part there are very minute white tortuous canals, which appear to communicate with the straight tubes of the cones. All beyond this is entirely conjectural.

The kidney, therefore, cannot be said to possess parenchyma or proper substance. The idle distinctions into cortical and medullary ought to be rejected as remnants of an exploded theory.

The kidneys are supplied with blood from the aorta by Bloon-veins, the renal arteries. Issuing at right angles from the lateral regions of the abdominal aorta, below the superior mesenterics, these vessels pass directly into the fissure at its superior and anterior part, the left behind, the right occasionally before the renal vein, but crossing its direction. The calibre of these vessels is considerable, about three lines at least; and they have been estimated to convey the sixth part of the blood of the abdominal aorta. The left artery is about one inch long, the right is the whole breadth of the vertebral column longer. In the renal fissure each artery divaricates into three or four consider- able branches, which enter the kidney a little above the attachment of the basin (pelvis). These vessels are again subdivided into an anterior series before, and a posterior cluster behind the infundibula, which they accompany to the papilla. Dividing more minutely, they form anastomotic arches, from the convexity of which proceed minute vessels, radiating into the granular substance of the gland. These vessels are distributed principally to the granular matter at its calyloid surfaces, in which the tubular cones are lodged.

The veins are arranged exactly in the same manner, and connected with the renal trunk, much as the arterial branches are connected with it.

The kidney is supplied with nerves, accompanying the arteries, derived from a plexus inclosing the renal trunk, and which is originally formed from filaments of the solar of the great sympathetic.

The pelvis consists externally of a prolongation of the renal investment, a proper middle membrane, white, opaque, and fibrous, and an inner lining, which, though thin and semitransparent, presents the character of mucous membrane.

The upper extremity of each kidney is covered by the renal capsule, a substance of no peculiar structure, and the nature of which is unknown.

The basin forms the common termination of the renal funnels, and the commencement of the ureter. This is a membranous tube, of the diameter of a moderate-sized quill, passing between the renal basin, behind the peritoneum, to the posterior and inferior part of the bladder, in which the lower extremity opens. Each ureter is inclined to the mesial plane below. The right ureter is on the outside, and nearly parallel with the inferior cavity. Both cross the psoas at an acute angle, and below the common iliac arteries and veins. In the pelvis they cross the vas deferens in the male, and on reaching the bladder pass obliquely, from eight lines to an inch, through its coats, and open in the posterior margin of the lower fundus of that organ.

These tubes consist of fibrous membrane, lined by mucous and covered by filamentous tissue. It contains no muscular fibres, notwithstanding the assertions of some.

The ureters are supplied with blood derived from the renal, occasionally from the lumbar and spermatic, but more especially from the aorta by two ureteric arteries.

The urinary bladder is a muscular membranous bag, spherical above and cubo-spherical below, placed on the lower region of the pelvis, behind the pubal symphysis, and before the rectum in the male, and the uterus in the female. From the peculiarity of its figure and relations, it is distinguished into a superior fundus, spheroidal, directed to the abdominal cavity; an inferior fundus, cubo-spheroidal, between the ureters and urethral opening; a neck (cervix), pyriform at the latter point; an anterior surface, corresponding to the posterior of the pubal symphysis; a posterior, corresponding to the rectum in the male and the uterus in the female; and lateral regions, corresponding to the ilio-ischial inner surface, and those of the obturator internus and levator ani.

In females generally the transverse extent of the bladder is greater than in the male, and in females after childbearing than in the virgin. In infancy its superior fundus is pointed and conical rather than globular,—a peculiarity derived from its foetal shape, which is pointed, with the urachus, a ligamentous chord proceeding to the navel, attached.

Structure. The bladder consists of a muscular coat, covered above, behind, and laterally by peritoneum, and lined by mucous membrane.

The peritoneal covering is continued from the anterior surface of the rectum, and the lateral regions of the pelvis over the posterior and lateral and part of the superior surfaces of the bladder, all of which are free; while the inferior fundus, the neck, and the anterior, are covered by filamentous tissue, connecting the organ to the neighbouring parts. This filamentous tissue is abundant, especially below.

The muscular coat, always distinct, varies in thickness in different individuals. In females, so far as we have observed, it is rather thicker than in males. The fibres run in all directions, but are strong at the superior surface, where some anatomists have arbitrarily distinguished them by the name of detrusor urinae. There are no fleshy pillars, mentioned by some, in the healthy state.

The neck is surrounded by a thick range of circular fibres, which has been denominated the sphincter of the bladder.

The mucous membrane, without villi or epidermis, is extended over the whole inner surface of the organ, and is continuous behind with that of the ureters, and before with that of the urethra. The space inclosed between these three orifices is named the vesical triangle (trigonum vesicae); and a minute duplicature of the mucous membrane at the urethral orifice is denominated the vesica urula.

The bladder is supplied with blood chiefly from the posterior iliac or hypogastric trunk, by means of the common pudic, the obturator, the ischiatic, and the hemorrhoidal. Of these, one vesical artery proceeds from the hemorrhoidal; another often comes off directly from the hypogastric as an inferior vesical; and in some instances they issue from the umbilical. The vesical nerves are partly from the sympathetic, partly from the sacral.

The capacity of the bladder varies in different individuals. In the female it is generally more capacious than in the male. In the healthy state it may contain a pound of urine, without extreme distension; and it is often capable of containing two, three, or four pounds. Its situation varies at different periods of life, and in different degrees of distension. In the fetus and infant, when the pelvis is small, the bladder is contained in the abdomen. In the adult in the ordinary state it is within the limits of the pelvis; but when much distended, its superior fundus, rising above the pubis, is in the abdomen. During pregnancy, also, it is thrust forwards and upwards by the gravid womb.

Urine, the fluid secreted by the kidneys, is particularly distinguished by containing, with various saline substances, urea, an animal principle containing 46 per cent. of azote. As the saline ingredients also abound in principles containing this element, it may be inferred that the chief purpose of the kidneys is to remove from the system a considerable proportion of nitrogen, which would either be injurious by its presence, or disturb the due proportion of the other elements.

The urethra, which terminates the urinary apparatus, is nevertheless common to it with the reproductive organs. The male urethra especially is more connected with the reproductive than the secretory organs. In the female, in whom alone this canal is proper to the latter, it is a short muco-membranous tube, terminating in a papillated orifice in the superior anterior wall of the vagina.

PART III.

ANATOMY OF THE ORGANS PERTAINING TO THE REPRODUCTIVE FUNCTIONS.

These organs, by the possession of which the individuals of the human race are distinguished into two sexes, male and female, consist in the former of impregnating, and in the latter of the impregnable organs. The former may be again distinguished into preparing and transmitting The male organs consist of two glandular organs, named testicles with excretory ducts, for secreting the impregnating fluid, and an organ for transmitting it to those of the female.

The testicles (testes) are two ovoidal bodies contained on each side of the mesial plane in a cutaneous-cellular sac named the scrotum, attached to the anterior inferior part of the pubic symphysis.

The scrotum consists of skin with very thin corion, resting on loose filamentous tissue, which forms on the mesial plane a thick wall, separating the right half of the scrotal bag from the left. On the median line is a superficial groove, named suture (raphe), at which the corion and filamentous tissue, elsewhere loose, are united into a solid and firm substance. Most of the old anatomists mention a muscular layer known by the name of dartos, and to which they ascribe the contraction of the scrotum on exposure to cold; but the existence of this muscular layer is not supported by inspection. The scrotal skin is well supplied with arteries, and especially veins connected with those of the epigastric, external iliac, femoral, obturator, and external pudic, the branches of which anastomose freely. The nerves are from the lumbar, obturator, and crural.

The scrotal filamentous tissue incloses on each side a thin membranous sac of a pyriform shape, with the base below, and tapering to a neck above. Adherent on the outside to the filamentous substance, this membranous sac is free and smooth within, except at the neck, where it embraces a part distinguished by the name of spermatic chord. This, which is the sheath-like or vaginal coat (tunica vaginalis), is distinguished into two parts, an inferior pyriform, forming a cavity for the testicle, and a superior cylindrical, covering the spermatic chord, and adhering to it. This membrane is said to be fibrous externally; but it appears to be merely condensed filamentous tissue. Within it is evidently a transparent serous membrane, both in qualities and distribution. It is continued from the adherent part of the chord downward, and over the testicle.

Within the cavity of the former are contained the testicles, both suspended by the spermatic chord, with the epididymis behind. Their substance is inclosed in a firm, opaque, white, fibrous investment, covered by a thin transparent membrane, reflected from the vaginal coat. The former is the tunica albuginea, or proper tissue of the gland; the latter is the vaginal coat of the testicle (tunica vaginalis testis).

The testicle consists of minute irregular-shaped granules, of a white or gray-white colour, soft, closely compacted, and with numerous capillaries distributed through them. More minutely examined, these are found to be capillary tubes of extraordinary length, folded on themselves, and contorted so as to occupy a small space, and when unfolded extending, according to some anatomists, 16 feet, according to others to 25 or even 100 ells. These long tortuous tubes, which are named the seminiferous (ductus seminiferi), are estimated at about 300 in number. They communicate by one extremity with the blood-vessels and lymphatics of the testicle, and by the other, after several unite into one common duct, terminate in about 20 larger tubes, denominated efferent ducts (vasa efferentia), which, united in a cluster by means of filamentous tissue, and invested by part of the tunica albuginea form at the upper part of the gland a whitish cylindrical body, about six lines long and two broad, distinguished by the name of the process of Highmore (corpus Anatomy Highmorei). These efferent vessels unite and form a single tube of great length, which, folded on itself by innumerable turns, connected by filamentous tissue, and invested by tunica albuginea, constitutes the epididymis, attached by its head to the testicle, and by an incurved extremity epididymis named tail, continuous with the common excretory duct (vas deferens).

The latter is a long fibro-cartilaginous tube, ascending upwards from the tail of the epididymis, and making defereins or part of the spermatic chord, with which it enters the seminal abdomen at the inguinal aperture. At the inner margin duct of this it separates from the chord, and descends into the pelvis, first by the side, then at the posterior and interior fundus of the bladder; and, approaching that of the opposite side with the vesicula seminalis on the outer margin, each vas deferens is in contact with the other at the base of the prostate gland. Here each receiving a tube from the corresponding vesicula, forms a common duct (ductus ejaculans), which traverses the prostate, and terminates in the urethra about one inch and a half from its vesical end, on each side of the eminence named verumontanum.

The spermatic chord, by which the testicle is suspended, spermatic consists of the spermatic artery or its divisions, derived in general from the aorta, two or three spermatic veins, several lymphatics, and the vas deferens, inclosed in filamentous tissue, and covered by a slip of muscular fibres denominated the suspensory muscle (cremaster, tunica erythroides), detached partly from the internal oblique and transverse of the belly, fixed partly at the inner surface of the ligament of Poupart and the tuberosity of the pubis.

The spermatic artery divaricates into several branches, which are distributed, after a few sent to the epididymis, among the seminiferous ducts. They communicate with numerous tortuous veins, which are collected into a cluster known by the name of the pampiniform body, situated immediately below the tunica albuginea.

Below the inferior fundus of the bladder, on the outside of that organ, are placed two bodies, oblong, flattened, vesicles pyriform, with the base behind, composed at first sight of a series of cells separated by septa. Each of these bodies, which have been named the seminal vesicles (vesicule seminales), consists of a long tortuous membranous tube, convoluted on itself; and with the folds aggregated by bridles of filamentous tissue, which convert it into communicating sacs. The cavity of this canal, which communicates with the urethra by a tube, common to the vesicles and the vasa deferentia, has been supposed to serve as a reservoir for the seminal fluid after secretion by the testicles; but this supposition is by no means verified, and is open to several objections.

The transmitting organs consist of the penis with the urethra and prostate gland.

The penis, the shape of which is well known, consists of two parts, the cavernous body (corpus cavernosum), and the spongy body (corpus spongiosum) containing the urethra. The cavernous body, single before, bifurcated behind, may be described as two cylindrical bodies, inclosed in a fibrous investment, which, uniting them on the mesial plane, forms a partition (septum medianum), perforated nevertheless with orifices for vessels. The divaricating posterior extremities (crura) are firmly attached to the ischio-pubal rami on each side. The intermediate triangular interval is occupied by the perineal filamentous tissue, fat, the perineal muscles, and the spongy body in the middle. Above and before, both are connected to the pubic symphysis by a triangular, flat, fibrous substance, named the triangular or suspensory ligament. The spongy body is a cylindrical cellulo-vascular tube, inclosing the urethra, and occupying the middle depression, along the lower surface of the cavernous body, from its anterior extremity, where it constitutes the glans, to the angular bifurcation of the cavernous body, where it is expanded into a substance denominated the bulb of the urethra. The spongy body is invested on the side and below by integuments only.

Both these parts, but especially the cavernous body, consist of numerous minute arteries, communicating directly with elongated and dilatable veins, and constitute the best example of erectile arrangement in the body. The injection of these vessels constitutes the erection of the penis, and induces the contraction of the urethra necessary to expel the seminal fluid. The two extremities of the spongy body, the glans before and the bulb behind, form the limits of the erectile tissue round the urethra. The anterior extremity is covered by loose skin, which forms the foreskin (prepuition), and, in the shape of a thin semimucous coronion, provided with epidermis, is continued over the glans, from which it passes insensibly into the mucous membrane of the urethra.

With the penis several muscular organs are connected. The ischio-cavernosus and transversus perinei on each side connect the cavernous body to the ischium; and the bulbo-cavernosus connects it to the bulb of the urethra. Mr Houston of Dublin has lately discovered a packet of muscular fibres situate between the pubic arch and the penis on each side, which, by compressing the dorsal vein, may, he imagines, contribute to erect the organ.

The cavernous and spongy bodies are supplied with blood from the terminal end of the internal pudic artery, by means of two vessels, the cavernous and the dorsal. The bulb receives branches from the transverse perineal artery.

The prostate gland is a body coidiform or flat, conoidal in shape, with the base behind and the apex before, corresponding to the vesical end of the urethra, situate behind the pubal symphysis before, and below the neck of the bladder, in the angle between it and the rectum, and between the levator ani of each side.

It is distinguished into three lobes,—two lateral, united on the mesial plane,—and a small cellulo-vascular slip in the angle between them, towards the base. In structure it is composed chiefly of minute arteries and veins ramified in a firm, fleshy, filamentous tissue, amidst which are placed follicles with minute ducts, which terminate in larger tubes, varying in number from seven to twelve, the apertures of which are on the sides and the surface of the urethra. These follicles secrete a viscid liquor, the use of which is unknown. From the fact, however, that, when the prostate gland is diseased or injured, the sexual appetite is languid or extinguished, it may be inferred that the prostate is essential to the generative functions in the male. It is analogous to the uterus in the female.

With the prostate may be mentioned the accessory glands of Cowper, two small bodies, oblong-round, placed on each side of the urethra, before the prostate. They appear to be mucous follicles on the large scale.

The urethra is a membranous canal, extending from the neck of the bladder in the pelvis to the extremity of the glans, where it terminates on the surface by an aperture (orificium urethrae), consisting of two lateral segments. Its length and width vary in the erect and unerected state of the penis. In the latter it is about seven or eight inches long, and its calibre is about three lines, but admitting of distension beyond this. According to the parts with which it is connected, it is distinguished into four different portions: 1st, the prostatic, about one inch; 2d, the membraneous, from one to one inch and a half; 3d, the bulbous, scarcely one inch; and, 4th, the spongy portion, occupying the anterior part of the canal, inclosed by the spongy body.

The surface of the urethra is a mucous membrane supplied with follicles, and moulded into blind sacs named lacuna, which appear to contain mucous ducts. Its capacity varies in different parts. Wide at the middle of the prostate, it is contracted in the membranous part, which is indeed the narrowest of the canal; it enlarges again in the bulb; and from this it preserves the same diameter to immediately behind the glans, where it forms a dilatation distinguished by the name of the navicular fossa navicularis). The apertures in this canal have been already mentioned to be, besides that of the bladder, one ejaculatory on each side of the cervumontanum, from seven to ten excretory apertures from the prostatic ducts, and one aperture from each accessory gland. The mucous membrane of the membranous and spongy portions presents longitudinal folds, which appear to be connected with the occasional distensions of the tube for the expulsion of the urine.

The urethra, straight in direction on the mesial plane, is incurvated within the pelvis from behind forwards, so that its concave incurvation incloses the pubal arch, while its convexity is turned to the perineum. The pendulous state of the penis, when unerected, causes it to acquire another incurvation without the pelvis, with the convexity directed upward. These curvatures are considerably exaggerated in engravings. The first round the arch of the pubis is much less angular than it is delineated.

CHAP. II.—THE FEMALE OR OOTROPHIC ORGANS.

The female generative organs consist of the ovaries, the uterine or Fallopian tubes, the womb, and the vagina. These organs are contained in the pelvis.

From the time of Steno, anatomists have given the name ovaries or eggbeds (ovaria) to two ovoidal bodies, about the size of a pigeon's egg, placed one on each side of the womb in the pelvis, in a duplicature of peritoneum termed the broad ligament (ligamentum latum) of the uterus. Convex and free on their anterior and posterior surfaces, and tapering towards each extremity, their lower margin is straight or slightly concave, with a vascular sinuosity. The external extremity is contiguous to a round solid chord (ligamentum teres), forming the anterior margin of the broad ligament, and proceeding from the womb to the internal orifice of the inguinal canal and the pubal extremity of the ligament of Pompert, and by which the uterus is retained in the pelvis. Each ovary weighs about one drachm and a half.

Covered externally by peritoneum, stretched over a fibrous membrane of some firmness, the ovaries consist of vesicles—a pulpy brownish-gray substance, very vascular, in which are embedded minute bodies of vesicular appearance and oval shape, varying in number from 15 to 20. These bodies, which, from the time of De Graaf at least, have been regarded as ova or embryal atoms or germs (ova Graafiana, ovarii vesiculae), consist of a thin membrane containing a viscid, reddish, or yellow fluid.

The ovary is supplied with blood from arteries analogous to the spermatic of the male.

Previous to puberty the ovaries are smooth in surface and entire. After this period, both in females who have had children, and even in virgins, they are marked on the surface by minute depressions, which have been denominated cicatrices, and which are believed to be the consequence of minute breaches of the ovarian tunics, occasioned by the escape of the vesicles from the surface of the ovary. There is no proof that these cicatrices are the inevitable result of sexual intercourse. Small before puberty, at that period they acquire considerable size, and Special retain them till the age of 45 or 48, after which they shrivel and shrink to a very small size.

The Fallopian or uterine tubes are the excretory ducts of the ovaries. They are cylindrical tubes about four or five inches long, contained in the anterior fold of the superior margin of the broad ligament, between the round ligament and the ovary, and connected by their lower extremity with the superior angles of the womb. Their superior extremity, which is loose, is surrounded by a fringed or laciniated slip of peritoneum, in the centre of which is seen the upper or peritoneal aperture (orificeum superius), larger than the calibre of the canal, which admits a hog's bristle, but contracts at the lower or uterine extremity (orificeum uterinum), which is situate in the upper angle of the inner surface of the womb.

Covered by serous membrane externally, lined by thin mucous membrane with follicular glands, the Fallopian tubes consist of fibrous tissue interposed between these two. Below, however, at their junction with the womb, they seem to partake of the structure of that body.

The womb (uterus, matrix) is a hollow organ with thick walls, shaped like a conoid, flattened before and behind, situate on the mesial plane in the pelvic cavity, between the bladder before and the rectum behind. Small before puberty, at that period it is about 2½ inches long, 1½ broad at its widest part, and weighs 7 drachms to 1½ ounce. It is distinguished into the fundus, body (corpus), and neck (cervix); the first free, directed upwards; the second also free, between the bladder and rectum; and the third connected within and below to the vagina. At each side of the fundus is a corner or angular part, which communicates with the uterine extremity of the Fallopian tube. The neck of the womb may be distinguished into the external or peritoneal, and the internal or mucous neck, which terminates in an elliptical opening, with rounded, thick, firm margins, not unlike the mouth of the tench, and named therefore os tineae, as well as os uteri. These lips become rough and irregular in women after child-bearing, in consequence of the distension during parturition.

The cavity of the womb is small compared with the volume of the organ, in consequence of the thickness of its containing walls. It is triangular in shape, with the base at the fundus, and the apex at the neck. The superior angles are small recesses, in which the uterine extremity of the Fallopian tube of each side opens. The cavity is much contracted at the neck, forming a short cylindrical canal, the lower aperture of which is the os uteri, communicating with the vagina.

Covered externally by peritoneum, the womb consists of a peculiar thick, firm, whitish substance, lined by mucous membrane. This intermediate matter, though neither red nor distinctly fibrous, has been very generally regarded as muscular. Its contractile powers during parturition it is impossible to doubt. But while it is difficult to reconcile this phenomenon with the absence of muscular tissue, it must be allowed that it is much more easy to maintain than demonstrate the unequivocal appearance of muscular fibres. On this topic the reader may consult a paper by Mr Charles Bell, in the 4th volume of the Medico-Chirurgical Transactions; and an elaborate account of the different ranges of muscular fibres in the uterus, by Madame Boivin, an eminent Parisian accoucheuse, in her Mémoire de l'Art des Accouchemens, Paris, 1824.

The uterine mucous membrane is thin, but reddish-gray, villous, and marked by numerous pores, the apertures of blood-vessels, most probably those which secrete the menstrual fluid. At the neck it is provided with muciparous glands, which are the seat of several of the forms of leucorrhoea.

The blood-vessels of the uterus are derived partly from the spermatic, partly from the hypogastric. The former, after passing between the folds of the broad ligaments, and giving branches to the tubes, enter the uterine substance by its lateral regions. The second, named the uterine, after sending branches to the vagina and neighbouring parts, ascend along the margins of the organ, and are distributed to its fundus.

The uterine veins correspond to the arteries in course and connections. In the walls of the organ they form large sinuses, very distinct after parturition.

The uterine lymphatics are connected with those of the pelvis and hypogastric region. The nerves, which are numerous, proceed from the lower extremity of the great sympathetic, from the renal plexus, the spermatics, the last lumbar nerves, and the sacral.

The womb is the proper ootrophic organ, to the inner surface of which the ovum is attached by a vascular body denominated the placenta or after-birth.

The vagina is a membranous vascular tube, situate on the mesial plane, behind the pubal arch and urethra, and before the rectum, and extending from the neck of the womb in the pelvic cavity to the external outlet (vulva), where it is continuous with the surface. Not exactly cylindrical, but flattened before and behind, its length is about four inches, its breadth one, but very distensible. It is generally distinguished into the upper vaginal recess (vagina fundus), inclosing the neck of the womb behind the os tineae, the lower vagina (vagina propria), and the vaginal opening (vulva).

The vagina consists of mucous membrane surrounded by filamentous tissue, a vascular network, and some muscular fibres. The mucous membrane, which is red below, gray above, and not unfrequently marbled, soft and spongy, is disposed in numerous large transverse and semicircular folds (rugae) on the anterior and posterior surfaces. In the recesses of these folds are numerous pores, evidently the source of the mucous viscid secretion which is so abundant on this membrane, during sexual excitement, at the period of parturition, and morbidly in gonorrhoea in the female. On the lateral regions it presents pyramidal eminences (popillae).

The mucous membrane is connected by filamentous tissue to another, which in the vicinity of the uterus is compact, firm, and elastic, and below, towards the orifice, is thinner, and contains a network of numerous communicating vessels, in which the blood is occasionally accumulated in the manner of erection. The lower extremity is inclosed laterally by some muscular fibres (constrictor vulvae), which are believed to have the effect of contracting the vagina voluntarily, and by which, when continued, as they occasionally are, to the base of the labia magna, women, according to Soemmerring, may move these parts. The vaginal membrane is provided with lymphatics connected with those of the pelvis. The nerves, which are numerous, and some of which appear to terminate in the pyramidal eminences, are derived partly from the sacral, partly from the crural trunks.

The vagina terminates in the vulva, an opening formed within by the clitoris before, the hymen behind, and the nymphae or labia parea on each side; externally by the mons veneris before, the frenum and navicular fossa behind, and the labia magna on each side.

The clitoris is a small, oblong, conical process, consisting of erectile vessels, covered by mucous membrane, attached to the lower margin of the pubal symphysis. The hymen is a crescentic fold of mucous membrane, surrounding the sides and posterior part of the vagina. The small lips or nymphae (labia parea) are two crescentic bodies, consisting chiefly of erectile vessels, contained within a duplicature of semimucous membrane. With these the inner surface of the labia is continuous; and they consist Connected with the female ootrophic organs are the breasts or mammae.

The female of the human species has only two breasts; and their position on the anterior and superior part of the thorax, on each side of the mesial plane, is a character which, with those of the locomotive apparatus, indicates distinctly the erect biped attitude.

Of a hemispherical or conical shape, the female breast consists of a glandular organ, named the mammary, surrounded by adipose tissue, and covered by integuments. It is distinguished into the breast (mamma), the nipple (papilla, mammille), and a coloured ring of skin (areola).

The gland is of a flat, rounded figure, and consists of lobes of white pulpy substance, separated from each other by filamentous tissue, and which may be resolved into granules or acini about the size of millet seeds, which again are composed of minute oblong vesicles disposed in a radiating manner. From the granules or acini proceed minute tubes named the lactiferous (ductus lactiferi, tubuli galactophori), which uniting into larger tubes, varying in number from 20 to 30, terminate in the centre of the mammary gland, behind the areola in conical dilated sacs (sinus), varying from one or two to three lines in diameter. These galactophorous ducts, which are larger than any other gland, are formed of mucous membrane, which extends into the sinuosities, and is at the nipple identified with the skin. Several of the lactiferous tubes are said to originate from the adipose tissue of the breast; but this seems merely to indicate that they communicate with the vessels of this substance. The lactiferous tubes are distinct before puberty, small in the virgin, and in general in the sterile, and during the intervals of pregnancy, and large only at the close of that period, and during the process of suckling.

The nipple of the female breast is a flat, conical process, the shape of which is well known, consisting externally of skin, with thin delicate corion and epidermis, internally of mucous membrane, and an intermediate network of dilatible arteries and veins mutually and freely communicating. These parts are united by filamentous tissue, which varies in quantity at different periods. But from the vessels now mentioned the nipple derives its property of occasional erection, especially under the influence of mental emotions.

The breast derives its blood from the internal mammary, the intercostals, and the thoracic or external mammary, the branches of which penetrate between the lobules of the gland. It has lymphatics, though not more abundantly than any other organ. The nerves are chiefly cutaneous.

The mammary gland is separated from the pectoral muscle by a thick cushion of adipose substance, on which it rests; and it derives a gentle conical elevation from the subcutaneous adipose tissue. The mammary skin is remarkable for the delicacy and softness of the corion.

CHAP. III.—THE PRODUCT OF GENERATION.

The ovum or impregnated germ, the result of the union of the sexes, consists of an embryo or new animal, inclosed in several membranes, and attached to the inner surface of the uterus by a vascular mass.

Of the membranes, one, the decidua (epichorion), belongs to the uterine surface; the other two, the chorion and amnion, belong to the fetus or embryo. The decidua consists of two parts, an external (decidua vera), and an internal (decidua reflexa); both modifications of albuminous secretion. The chorion, the outer covering of the fetus, is a thin transparent membrane, covered with villosities on both surfaces, but especially the external. The amnion is a thin transparent membrane, adhering feebly by its external surface to the inner of the chorion, and inclosing a watery fluid, variable in quantity, in which the fetus, suspended by the umbilical chord, floats.

The umbilical chord (funic umbilicalis) consists of, 1st, The umbilical vein and two arteries, inclosed in—2d, a soft, semifluid, gelatinous substance, named from Wharton gelatina Whartoniana; 3d, the urachus, a ligamentous chord proceeding to the superior fundus of the bladder; and, 4th, the umbilical sheath (vesica umbilicalis). In the early period of uterine life, it also contains part of the intestinal canal, the vesicula umbilicalis either partly or wholly, and the omphalo-mesenteric vessels. Of these parts the umbilical veins and arteries, by their connection with the placenta, are the most important. The others our limits allow us merely to indicate.

The placenta is a round or orbicular, thick, cake-shaped mass, with two surfaces, a filamento-vascular, attached to the inner surface of the womb, and a smooth membranous one, to which the umbilical chord is fixed. It consists of lobular portions (cotyledones), separable from each other, and each of which receives a small artery derived from the uterine trunks, which are much enlarged during pregnancy. The average weight of the placenta is 1 pound 2 ounces.

The placenta, according to Dr Hunter (Anatomical Description of the Human Gravid Uterus, edit. by Dr Baillie, Lond. 1794), consists of two portions; a fetal or umbilical, and a maternal or uterine part.

The fetal part is composed entirely of ramifications of the umbilical arteries and umbilical vein. These, dividing with extreme minuteness, are distributed to all parts of the placenta. The branches of the umbilical arteries finally terminate in the umbilical vein, and have no other termination; all the branches of the umbilical vein arise from the umbilical arteries, and have no other commencement.

The maternal part consists of a whitish-coloured substance, which is spread over the outer surface of the placenta in the form of a membrane, and sends off innumerable irregular processes, which pervade its substance as deep as its inner surface. These are everywhere so blended and entangled with the ramifications of the umbilical system, that it is impossible to discover the nature of their union. They are interwoven in such a manner, however, as to leave innumerable small vacuities or cells between them, which communicate freely with each other through the whole mass. The maternal part is full of large and small arteries and veins, none of which are derived from the vessels of the fetal part, but all from the arteries and veins of the uterus. All the arteries are serpentine, and much convoluted; the larger, when injected, are almost of the size of crow-quills; and, after little or no ramification, they terminate abruptly in the cells already described. This is their only termination. The veins have frequent anastomoses, pass in a very slanting direction, and generally appear flattened; some of them are as large as a goose-quill, but many of them very small; and all arise abruptly from the cells of the placenta. This is their only commencement.

The umbilical arteries, which are branches of the hypogastric, ascend beside the bladder and before the rectum, approach each other, pass over the fundus of the bladder, and reach the navel with the urachus. There they alter their direction, and are wound round the umbilical vein, which proceeds from the placenta by the same aperture (the navel) by which the arteries escape. These arteries, which are almost equal in diameter to the hypogastric or posterior iliac, of which they appear to be the continuation, diminish in size after birth, and appear then to be mere branches. Eventually they are obliterated and converted into solid chords, about 1 inch from their origin.

The umbilical vein, which is larger than both arteries taken together, is the common trunk of the veins of the re- The placenta, from which it proceeds through the umbilical opening or navel, in the folds of the falciform ligament, to the umbilical fossa of the liver, where it divides into two branches, one large, proceeding to the vena cava, and another small, into the vena cava, known by the name of venous duct or canal (ductus venosus). The umbilical vein is distributed chiefly to the left lobe of the liver.

The structure of the fetus differs in many respects from that of the adult; and these differences depend on the stage which the process of development has attained. As it is impossible to trace the history of this interesting process within the limits of this sketch, we shall merely specify the principal anatomical peculiarities by which the fetus is distinguished from the full-grown subject.

A large vascular body, denominated the thymus gland, is found to occupy the anterior mediastinum. The kidneys are covered by triangular filamento-vascular bodies, named renal capsules, larger than the glands themselves, and supplied with large blood-vessels. The liver is very large, especially its left lobe, and occupies not only the right hypochondriac and epigastric, but the left hypochondriac region. The lungs are compact and of a deep red colour, and sink in water; and the bronchial tubes are collapsed and void of air. In the heart the right and left auricle communicate freely by an oval aperture in the septum. The pulmonary artery, rising from the right ventricle, divides, not into two, as in the adult, but into three branches; one on each side, going to each lung, small, and conveying little blood; and one in the middle, proceeding to the aorta, about 9 lines long, named the arterial canal (ductus venosus arteriosus). The umbilical vein, proceeding to the liver, is distributed by about 15 or 20 branches to the left lobe of that organ. In the horizontal furrow it divides into two branches, one of which goes to the portal vein, the other, apparently the continuation of the trunk, opens into the vena cava, under the name of venous duct (ductus venosus), forming with it an angle acute above, and provided with a valve. The kidneys consist of lobules as numerous as their tubular cones, which indeed these lobules are, separate from each other. The urinary bladder is not within the pelvis, but in the abdominal part of that cavity; and it terminates above in a point, to which a ligamentous process (urachus), connecting it to the navel, is attached. In the male, the testicles are contained in the abdomen, often immediately behind the internal aperture. Lastly, till the seventh month the pupillary aperture is closed by a peculiar membrane.

The engravings with which the foregoing article is illustrated have been sufficiently explained by literal or numeral references, in the course of description. We have only to add, that fig. 1 and 2 of Plate XXXI., from Soemmerring, are intended to show the important parts at the lower surface of the brain; fig. 3, from the same, the relations of the middle band, vault, and septum; and the other two, from Reil, the internal arrangement of the nucleus. Plate XXXII., from Scarpa, shows the phrenic nerve, and the thoracic part of the pneumogastric and sympathetic, with the cardiac plexus and nerves. Plate XXXIII., from Cruikshank, gives a general view of the arrangement of the lymphatics.

In the foregoing account of the anatomy of the human body, many points have been treated in a manner too short and cursory, considering their importance; and in the attempt to restrain it within due limits, the heads of several have been only indicated. It was the intention of the author to introduce all the new information in microscopical anatomy, which the researches since the year 1832 had furnished. This however, particular circumstances render impracticable. For those who wish to study the subject more minutely, besides the works occasionally mentioned, we refer to the following general systems and treatises.

1. S. Th. Soemmerring De Corporis Humani Fabrica: Latio donata, ab ipso auctore aucta et emendata. Tom. i. De Ossibus, Trajecti ad Rhenum, 1794. Tom. ii. De Ligamentis Ossium, 1794. Tom. iii. De Musculis, Tendinis, et Bursis Mucosis, 1796. Tom. iv. De Cerebro et Nervis, 1798. Tom. v. De Angiologia, 1800. Tom. vi. De Spleenologia, 1801. This work, which is excellent so far as it goes, and is particularly distinguished for clear arrangement, and distinctness, precision, and accuracy of description, is incomplete. It wants the anatomical description of the eye, the ear, and the generative organs in the two sexes. The first two defects, however, are ably supplied by the author in his Abbildungen des Menschlichen Auges, fol. Frankfort, 1801; and Abbildungen des Menschlichen Hoerorganes, fol. Frank, 1806.

Of this work a new and greatly enlarged edition, in which the deficiencies above noticed are ably supplied, was published at Leipsic between 1841 and 1844. See historical sketch.

2. Traité d'Anatomie Descriptive; par Xav. Bichat, Médecin du Grand Hospice d'Humanité de Paris, Professeur d'Anatomie et de Physiologie. Tome i. à Paris, 1801; tome ii. et iii. 1802; tome iv. par M. F. R. Buison, 1803; tome v. par Philib. Jos. Roux, Prof. d'Anatomie, 1803. The death of the author interrupted the publication of this work in the middle of the third volume, the first part of which only is by Bichat; while the sequel of that volume is compiled from the materials left at his death. This constitutes the most accurate descriptive system yet extant; and the strongest proof of its superiority is, that its descriptive portion has been very closely copied in the work of Colquet.

3. Cours d'Anatomie Médicale, ou Elements de l'Anatomie de l'Homme, avec des Remarques Physiologiques et Pathologiques, et les Résultats de l'Observation sur le Siège et la Nature des Maladies, d'après l'Ouverture des Corps; par Antoine Portal, Prof. de Méd. &c. &c. Paris, 1803, tomes cinq. A complete and accurate work.

4. Handbuch der Menschlichen Anatomie, von J. F. Meckel, Band i. ii. and iii. Halle und Berlin, 1815. This work was translated into French in 1825, by MM. Jourdan and Breschet.

5. Traité d'Anatomie Descriptive, redigé d'après l'ordre adopté à la Faculté de Medicine de Paris; par Hippol. Cloquet, Docteur en Medicine, &c. This is a very good system of descriptive anatomy. In arrangement, M. Cloquet follows that of Bichat; and in description the first volume, and a great part of the second, are copied almost literally from the first, second, and part of the third of that author. It would have been quite as well had this been avowed; for it deprives Bichat of much of his most unquestionable merit, and gives an unfavourable impression of the candour of M. Cloquet. In the sequel of the second, on the vascular system, and the organs of respiration and digestion, the author has availed himself of the materials of Soemmerring.

6. Elements of the Anatomy of the Human Body in its sound state, with occasional remarks on Physiology, Pathology, and Surgery, by Alexander Monro, M.D., &c. 2 vols. Edinburgh, 1825.

On the subject of General Anatomy, on various details on the anatomical divisions and peculiarities of the Brain, on the minute structure of the Lungs, the Liver, the Kidneys, and other glands, we refer here in general, besides the works mentioned in the close of the historical sketch, to the following treatises.

7. Elements of General and Pathological Anatomy, presenting a view of the present state of knowledge in these COMPARATIVE ANATOMY.

PART I.

ANATOMY OF THE ORGANS OF RELATION.

CHAP. I.—COMPARATIVE OSTELOGY.

Red-Blooded Animals only can be said to possess that assemblage of bones denominated skeleton; and as in these the most constant part is the vertebral column, it furnishes the general character of Vertebrated. The shells of the Mollusca and the Crustacea have been generally regarded as a species of internal skeleton; and in the circumstance of affording mechanical support and external protection, they indeed resemble the skeleton of the Vertebrata. But neither in mode of development nor in chemical constitution can they be regarded as of the same nature. Hence it is only in the vertebrated classes that it is requisite to study the peculiarities of the skeleton.

In general characters the bones of the Mammalia resemble those of the human subject. Like them, they are white, firm, elastic, and incompressible. They consist also of compact and reticular or cancellated tissue. In the lower animals the latter kind of structure is in general coarser and looser than in man; and in the Cetacea especially the cavities are large. In the carnivorous animals the compact structure is exceedingly dense, and gives the bone much greater weight than in other animals. In the Cetacea also the acoustic or lithoid portion of the temporal bone is of a marble hardness.

The bones of the Mammalia may, like those of man, be distinguished, according to their mechanical form, into long, flat, and short bones. Though the first class in general possess a medullary canal, this cavity is imperfect or wholly wanting in the bones of the Cetacea and Amphibia.

The cavities denominated sinuses are much more completely developed in several of the Mammalia than in the human skeleton. In the pig these cavities extend into the occipital bone; in the elephant they not only give the frontal bone extraordinary protuberance, but they extend into the parietal, temporal, and even the occipital bones, and contribute much to augment the volume of the head. In the ox, deer, and sheep, they communicate with the cavity of the horns.

The bones of Birds are in general whiter, firmer, and smoother than those of the Mammalia; and they consist of a firm, compact substance, which is elastic and hard in the bones of the trunk, and extremely brittle in those of the extremities. With the exception also of some of the thin, flat bones, as the sternum, they consist of thin, compact walls, inclosing large capacious cavities, which contain not marrow, but air, and which communicate by one or more minute holes with the windpipe and lungs. While these cavities, which may be regarded as the most perfect and advanced form of sinuses, diminish considerably the weight of the whole skeleton, by the density and completely cylindrical shape, they rather augment the strength. In the chick, and at birth, the bones are homogeneous and without cavities; afterwards they contain marrow; and eventually this disappears and gives place to air.

The bones of the Reptiles are not remarkable in any respect, unless in being void in general of medullary cavity. The absence of this canal was originally observed by Caldesi, and afterwards by Cuvier, in the tortoise; by Troja in the bones of the frog and toad; and by Carus in those of the turtle. In the crocodile, however, and in several of the lizard family, they are large and distinct. The bones of Reptiles also are less firm than those of Birds and Mammals.

The bones of Fishes are remarkable for great softness, flexibility, and elasticity. Those of the lamprey, shark, ray or skate, and sturgeon family, are soft, flexible, septicile, of a bluish white colour, translucent, and so elastic that a cutting instrument forced into them is speedily retarded by the resilient nature of the bony matter. From these characters, the bones of these families have been regarded as cartilaginous, and the fishes themselves have been distinguished by this character. (Pisces Cartilaginæ, Pisces Chondropterygii.) In the other fishes, the bones, though softer than those of Mammals, Birds, and Reptiles, present a greater degree of firmness and solidity, are whiter and more opaque, and are much less septicile, than those of the cartilaginous division. As in this respect, therefore, they approach the genuine bone of the Mammals, these are distinguished as fishes with osseous skeletons. (Pisces Ossei.)

The bones of both classes of fishes consist of a large quantity of gelatine, with a small proportion of phosphate The colour of the bones of fishes, though in general whitish gray, is observed to vary in certain genera. In the gar-pike (esox belone), for instance, they are green, and in the viviparous blenny (blennius viviparus), the sand lance (ammodytes tobianus), and two species of labris (the l. lapina and eruginoso), they assume a green colour after boiling. The causes of these varieties in colour are unknown.

SECT. I.—OSTEOLOGY OF THE MAMMIFEROUS ANIMALS.

The skeleton of the Mammalia bears a general resemblance to that of the human subject, in the construction, shape, and disposition of its component pieces. Distinguished, like that, into head, trunk, and extremities, we recognise the importance of the trunk, and especially of the spine, in the different classes of mammiferous animals.

The spine consists of separate vertebrae, which are conveniently distinguished, as in man, into cervical, dorsal or costal, lumbar, sacral, and coccygeal or caudal.

The number of cervical vertebrae is the same in animals with the longest and shortest necks,—in the horse, camel, and giraffe, and in the mole and ant-eater. They are always seven. The only exception is observed in the Ai or three-toed sloth (brachyphyllus tridactyla), which has 9 cervical vertebrae (Cuvier); and an apparent exception is presented in the dolphin and porpoise, in which the first two are consolidated into one; and in the cachalot or large-headed whale, in which the last six, sometimes the whole seven, are united or ankylosed. The last six are also united in the ant-eater and manis (Cuvier). Even in this state, however, the traces of the original separation are distinct.

In the ape the cervical vertebrae are distinguished from those of man chiefly by the spinous processes being stronger and not bifid, and in their bodies being projected more over each other before, so as to support the head more perfectly. In the Zoophaga the transverse processes of the cervical vertebrae are flattened from behind backwards, and those of the atlas are very large, both for supporting the head and giving attachment to the strong muscles employed in defence, attacking prey, or bearing it off. For the same purpose the spinous process of the axis is very prominent, while the others are short and directed towards the head. In the mole and shrew the cervical vertebrae, which are void of spinous processes, are simple osseous rings, which move easily on each other, probably to facilitate the frequent motions requisite in these animals in burrowing. In the hog the cervical transverse processes are compressed and broad before, so as to appear double. In the elephant the cervical vertebrae have short single spinous processes, and the bodies projecting over each other as in the ape. In the Ruminants the length of the spinous processes diminishes as the neck is elongated. Thus they are almost wanting in the camel and giraffe, in which the arched neck is much retro-flexed; and the same peculiarity is recognised in those of the horse.

From these facts it results that the length of the neck depends not on the number, but on the longitudinal extent, of the cervical vertebrae.

The dorsal, thoracic, or costal vertebrae are distinguished by forming the central fixed basis of the ribs; and their number depends on that of the latter class of bones, which is very variable. The number of costal vertebrae varies from 11, which is that of the Chinese monkey, common bat, armadillo, helmet-headed dolphin (delphinus globiceps), and Gangetic dolphin, to 23, which is that of the Unau (Bradypus didactylus). The most common number is 12, which is that not only of man, but of the orang-outang, silky monkey (simia marhikina), patas (s. patas), macaque (simia macaca), magot (s. imus), mandrill (s. mainimon), pongo (s. pongo), macaco (lemur catta), vampyre, great and horse-shoe bat, colugo (galeopithecus), shrew, hare and rabbit, agouti, flying squirrel, mouse and field rat, and camel and dromedary. The next most frequent number is 13, which is that of the mole, white bear, civet, the cat tribe (felis), the dog, wolf and fox, the didelphis tribe, the cavy, guinea pig and paca, the mouse tribe, excluding the two exceptions already mentioned, the long-tailed manis, the stag, the antelope genus, the goat, sheep, and ox, and the dolphin and porpoise. The number is 14 in the gibbon, coita, and weeping monkey, in the howling ape (simia beelzebul), the tarinsus, the brown bear, raccoon and coati, the weazel genus, the porcupine, hog, and giraffe. It is 15 in the lori, hedgehog and tenrec, in the badger, pangolin, and seal. The number is 16 in the glutton, hyena, ant-eater, American lamantin, and megatherium. In the horse, quagga, and dugong, they are 18; in the rhinoceros 19; in the Indian elephant and tapir 20; and in the Unau or two-toed sloth 23, which, as already stated, is the greatest number yet known.

In the ape family the dorsal vertebrae resemble those of the human subject, but their spinous processes are long, and erect in the macaca and magot. In the bats, instead of spinous processes, which are wanting, there are minute tubercles. The want of these, however, in sundry species, leaves the column comparatively smooth behind. In the proper quadrupeds these processes are larger, straighter, and stronger, as the head is weighty or supported on a long neck, in order to give attachment to the strong yellow cervical ligament. This peculiarity is very distinct in the giraffe, camel, ox, rhinoceros, and elephant. In the dolphin they are straight, and smaller than those of the loins.

The lumbar vertebrae vary in number still more, perhaps, than the cervical and dorsal; and this variety may occasionally be traced to the greater or less distinctness with which the sacral and coccygeal are distinguished. The smallest number is 2, which is that of the two-toed ant-eater, ornithorhynxus, and American lamantin; and the greatest 9, which is that of the lori. The most frequent number is 7, which is that of the greater part of the monkeys, the macauro, the great bat (noctula), the hedgehog, shrew, raccoon; the tiger, panther, puma, and cat, in the feline genus; the wolf and fox in the dog; the hare and rabbit; the whole murine genus except the hamster; and in the camel and dromedary. The next number in frequency is 6, which is that of the horse-shoe bat, the colugo (galeopithecus), the white and brown bear, the coati, the weasel genus, the civet, the lion, among the feline, and the dog among the canine genus, the didelphis and cavy genera, the hamster, the stag, antelope, goat, sheep, ox, horse, and quagga. The gibbon, coita, Ai, Echidna or Ornithorhynxus hystrix of English zoologists, six-banded armadillo, and dugong, have only 3 lumbar vertebrae; the orang-outang, pongo, and howling ape, 4; the vampyre bat 4; the hyena, armadillo, Unau, and tapir, 4; the jocko, tarsier, and common bat, 5; the badger and glutton, the porcupine, beaver, pangolin, long-tailed manis, hog, giraffe, gazzelle, chamois, and seal, all 5; and the agouti and flying squirrel have 8.

In the Quadrupedana and Zoophaga generally the outer side of each posterior articular process presents an apex turned backward, so that the anterior articular process of the next vertebra is locked between two eminences, which confine its movement much. Though this apex is found The number of sacral vertebrae is still more various, even in the species of the same genus. Thus, while in several of the ape genus, in the lori, in the vampire bat, the colugo (galeopithecus), the coati, and two of the didelphis, there is one sacral vertebra only, most of the apes have sacra consisting of 2, 3, 4, 5, or 6 pieces; the majority of other animals have 3 sacral vertebrae; the hedgehog, porcupine, guinea pig, paca, hare, tiger, several of the murine genus, the ant-eater, rhinoceros, camel, dromedary, chamois, goat, sheep, and ox, have 4; the elephant has 5; the Art 6; the Uanu 7; and in the mole, white bear, and quagga, they also amount to 7. The frequency of the three sacral vertebrae in the lower animals shows that Galen, who ascribes only 3 to the human subject, must have derived this inference from the former.

These vertebrae are in the mammalia narrower than in man, and their direction forms with the spine, instead of receding backwards, a straight line; an arrangement evidently connected with the horizontal position of the former. The shape of the sacrum in the lower mammals is that of an elongated triangle; and it is further remarkable, that in those species which occasionally assume the erect attitude on the hind leg, as apes, bears, and sloths, the width of the sacrum is proportionally greater. The sacral spines, which are short in man and the ape, become longer in the Zoophaga, and form a continuous ridge in the rhinoceros, most ruminants, and especially in the mole. In the vampire bat the sacrum forms a long compressed cone, the extremity of which is united to the ischial tuberosities, without sustaining a coccyx. The seal has two sacral bones; but the Cetacea, e.g., the dolphin and porpoise, are void both of sacrum and coccyx.

The coccygeal bones constitute the tail of the lower animals, and in many instances they are extremely numerous. The smallest number is 3, which is that of the magot (simia sylvanus, pithecus, et inae) or Barbary ape; and the greatest yet known is that of the ant-eater, in which they amount to 40, and the long-tailed manis, in which they amount to 45. Next to these may be placed that of the coatta 32, the baboon 31, the phalanjer (didelphis orientalis) 30, the marmoset (didelphis murina) 29, the pangolin 28, the silky monkey (simia rosalia) and black rat 25, the weeping monkey and howling ape 25; the panther, mouse, dormouse, and elephant, 24; the lion, beaver, water-rat, Norway rat, and field-rat, 23; the flying-cat, puma, cat, dog, marmot, and rhinoceros, 22; the otter, 21; the Chinese monkey, raccoon, civet, hare, and rabbit, 20; the tiger and wolf, 19; the macaque, glutton, martens, fat dormouse, dromedary, giraffe, and quagga, 18; the tarsier, shrew, camel, and horse, 17; and other genera and species, without any determinate order, descending so low as to 9, 8, 7, 6, and 4. The quilled duckbill (echidna, ornithorhyncus hystrix) has only 12 caudal vertebrae, while the common one (ornithorhyncus paradoxa) has at least 20. The gibbon and vampire bat are the only mammiferous animals, excepting the Cetacea, in which there are no coccygeal bones. It sometimes happens that a monkey or opossum loses a portion of its tail, when the truncated end is converted into a knotty excrescence, sometimes curious, always different from the taper point of the last coccygeal vertebra; and in this case it is difficult to determine the exact species.

In the Cetacea, in which the absence of pelvis affords no mark to distinguish the lower vertebrae into lumbar, sacral, and coccygeal, those below the dorsal may be regarded as lumbo-coccygeal; and their number is estimated by deducting that of the cervical and costal from the total number. The following table, which shows the number of the costal, the lumbo-coccygeal, and the total number of vertebrae, indicates that their number varies much in various genera of this family.

| Lamantin | 16 | 24 | 40 | |----------|----|----|----| | Dugong | 18 | 24 | 46 | | Narwal | 12 | 35 | 47 | | Delphin | 13 | 47 | 60 | | Turia | 12 | 29 | 41 | | D. Globiceps | 11 | 37 | 58 | | D. Griseus | 12 | 42 | 61 | | D. Gangeticus | 11 | 28 | 46 |

In general, however, if we reckon the first 2, 3, or 5 vertebrae after the costal as lumbar, it may be said that the caudal vertebrae of the Cetacea vary from 22 or 25, which are the numbers respectively in the lamantin and dugong, to 34, 38, and 42, at which they may be estimated in the dolphin. We shall see that, in the dugong at least, we are guided in this estimate by the rudimental bones of the pelvis.

The coccygeal or caudal vertebrae of the Mammalia may be distinguished into two kinds; those which contain a canal in continuity with that of the vertebral column and sacrum, and those in which the pieces are solid. The first, which are next the sacrum, have articular, transverse, and spinous processes, distinct in proportion as the animals move their tails. The latter are generally prismatic in shape, diminish in size towards the extremity, and have only slight tubercles for muscular attachments. Animals with prehensile tails, as the American ape (sapajous), have above, at the base of the body of each vertebra, two small tubercles, between which pass the tendons of the flexor muscles. By means of this mechanism these animals can twine the tail round the branch of a tree with sufficient force to support the weight of the body.

The Mammalia with long mobile tails have often two or three small supernumerary bones placed on the lower surface of the junctions of several of the coccygeal vertebrae, from the 3d or 4th to the 7th or 8th. These sesamoid bones give attachment to muscles. In the beaver, which employs its tail as a trowel, the transverse processes are remarkable for size, while the lower spinous processes are larger than the upper ones,—an arrangement which enables it to depress the tail forcibly when it beats the ground.

The shape of the chest in the Mammalia varies in general as the clavicles are present or wanting. In animals provided with clavicles, as the Quadrumania, bats, the squirrel, beaver, mole, ant-eater, hedgehog, and sloth, the shape of the chest approaches to the human, or is conoidal, and flattened before and behind. In those void of clavicles it is compressed laterally, from the smaller incurvation of the ribs; and the sternum makes a remarkable prominence, so that the transverse or intercostal diameter is less proportionally, and the sterno-vertebral is greater proportionally, than in man and the clavulated animals. In the long-legged animals, as the giraffe and those of the stag kind, this prominence of the sternum is sufficient to give it a keel-like appearance (thorax carinatus). In the carnivorous animals the chest presents its greatest longitudinal extent.

The number and shape of the ribs varies in the different tribes. In number, indeed, the ribs always correspond with that of the costal vertebrae. Thus, in the Quadrumania, Zoophaga, Rodentia, Edentata, and Ruminantia, they vary from 12 to 15 pair, with only three exceptions, the glutton, hyena, and ant-eater. In the Chinese monkey, common bat, and armadillo, they are a pair less than in While the quilled duckbill (echidna, ornithorhynchus hystrix) has only 15 ribs, the common duckbill (ornithorhynchus paradoxa) has 17; the horse and quagga have 18, the rhinoceros 19, the elephant and tapir 20, and in the Ursus or two-toed sloth they amount to 23, which is the greatest known number. On the whole, the most prevalent number is 13. In the carnivorous animals they are narrow and dense in structure. In the herbivorous they are large, broad, and thick. In the armadillo the two first ribs are large compared with the others. In the two-toed ant-eater, which has 16 pairs, they are so broad that they are imbricated over each other like the plates of a corset, and render the parietes of this animal's chest exceedingly solid. In the two species of duckbill (ornithorhynchus paradoxa and hystrix; echidna of Cuvier), the true ribs, in number 6, consist of two portions—a long or vertebral joined to the spine, and a short or sternal attached to the sternum. These portions are united by cartilage, so as to resemble the ribs of birds. The 9 or 10 false ribs terminate before in broad, flat, oval plates of bone, which are mutually connected by elastic ligaments.

The sternum, which is broad in the ourang and pongo, is narrow in the other species of ape, and consists of seven or eight pieces. In the vampire and all the bat family it is narrow, but presents before or below rather a prominent oxygous ridge or keel (carina), and an anterior extremity, broad on the sides, like a T, for receiving the clavicles. In the mole the clavicular extremity of the sternum is continued before the ribs, and is flat on the sides for receiving the two short clavicles. In the hog the sternum is broad behind and narrow before. In the rhinoceros, horse, and elephant, it is prolonged before and flat on the sides. In the Cetacea it is broad and thin, especially before.

Though the Quadrupedina have 8 cranial bones, the sphenoid often consists of two portions, one forming the orbital wings and the anterior clinoid processes, the other the temporal or large wings, the posterior clinoid processes, and the basilar fossa. The two parietal bones are early united into one in the Chiroptera and the other Zoophaga, in which, however, the frontal remains biparted by a middle suture. The temporal tympanum is separated from the rest of the bone by a suture, which is seldom obliterated in the feline, canine, and viverrina genera. The temporal tympanum is also separate in the Rodentia, and the frontal ununited. The parietal is united in some, as the hare, the porcupine, cavia, marmot, rat, and squirrel; separate in the mouse, fat dormouse, and rabbit. The frontal and parietal bones of the elephant are early united with the other cranial bones, and form a vault without trace of suture. In the hog, tapir, and hippopotamus, the two parietal bones form one piece, while the frontal bone is biparted; and though in the rhinoceros both are biparted, the frontal is early united into one portion. The sphenoid bone of the animals of this tribe long consists of two pieces, one forming the orbital wing; the other the temporal wings, which, it is to be further observed, are the smallest, in opposition to their proportional dimensions in man. In the Ruminants and Solidungula the frontal remains long parted by its middle suture; but the two parietals are represented by a single bony vault. The tympanum is always distinct from the temporal bone. In the seal and walrus the parietal and the frontal consist of two pieces. The lamantin has only one bony arch, representing the two parietal and the squamous part of the temporal bones, while the temporal tympanum is detached from the rest of the bone. In the other Cetacea the parietal bones are at an early period united to the occipital and temporal bones, so that the five form one solid portion. The auditory or pyramidal bone is always detached from the temporal, and adheres to the cranium by comparative soft parts only. The sphenoid is not only long separate, but consists of several portions.

Though, among the Quadrupedina, the cranium of the ourang-outang approaches that of man in shape, it differs nevertheless in the connections of the constituent bones. The temporal wing of the sphenoid bone is very narrow, does not reach the parietal, and touches the frontal only by its upper extremity, so that the temporal bone is partly articulated with the frontal. The temporal suture is not imbricated, but serrated. The same mode of connection is observed in the mandrill, macaca (s. cynocephalus), magot, and guenon (Cercopithecus), or tailed monkey tribe. In the American monkey the temporal wing of the sphenoid touches neither the frontal nor the parietal bones; but the temporal bone is articulated directly with the malar by its flat portion. In the American monkeys the frontal bone does not touch the temporal wing of the sphenoid, and the parietal is articulated to the malar. In the howling ape (simia beelzebul) the connections are as in man.

The connections of the cranial bones are in the Zoo-Comphaga the same as in man. In the Rodentia the sphenoid is joined to the frontal and temporal, without touching the parietal; and the orbital and temporal fossae are very small. In the armadillo, pangolin, and sloth, the connections are as in the Rodentia; but in the ant-eater the parietal bone, continued below the cranium, is united to the sphenoid at the posterior part of the orbito-temporal fossa.

In the elephant, though the cranial bones are at an early period consolidated into one, the auditory is always distinct from the temporal bone. In the hog, tapir, rhinoceros, and hippopotamus, the sphenoid is united to the parietal bone, and its temporal wings occupy a small space only of the orbital and temporal fossae. The orbital wings, though larger, appear small externally. The auditory bone, though distinct, is, however, united by its base to the margin of the auditory canal of the temporal bone. The sphenoid of the ruminants is articulated, as in man, with all the cranial bones; but its orbital wing, which is extensive, is principally concealed within the cerebral cavity, and covered by the orbital part of the frontal bone. In the Cetacea generally, all the sutures which remain after early life are squamous or imbricated.

The outline of the frontal bone in the ourang-outang is more irregular than in man, and the orbital arches are less subsurred. In the American monkeys its outline is triangular, and terminates in a point towards the vertex. In the others of this family (Simia), this bone is almost elliptical, and the orbital arches are nearly straight; and in the whole family these arches form, as in man, the anterior border of the frontal bone, in consequence of the narrowness of the root of the nose. In the makis it begins to widen, and the eyes become oblique,—a circumstance which gives their frontal bone a rhomboidal shape.

The frontal bone in the Zoophaga, and in all the subsequent Mammalia, except the Cetacea, forms an irregular prismatic or cylindrical surface with three faces—a superior, bounded before by the muzzle, behind by the cranial convexity and two lateral, descending into the orbital and temporal fossae on each side. The hedgehog, mole, shrew, ant-eater, some of the phoca, the morse or walrus, and the rhinoceros, have no proper orbital arches; and the frontal bone, though broad behind, is contracted and nearly cylindrical between the orbits. In the hippopotamus, the ruminants, and the one-hoofed animals, it enlarges, and forms a vault over each orbit. Lastly, in the Cetacea it is narrow from before backward, resembling a fillet stretched across the cranium, but descends beneath the maxillary bones to form the floor of the orbit. The parietal bones of the orang-outang differ from those of man only in their temporal margin being nearly straight. Those of the ape are narrower, and become more oblique-angled as the cranium is flattened. In the Zoophaga and Edentata they are almost rectangular. The single parietal of the Rodentia is nearly quadrilateral; but it is sometimes flat, sometimes rounded, sometimes surmounted by a crest. Of the single parietal bone of the ruminants, that of the stag, most of the antelope genus, the sheep and the goat, is broad, and sends on each side a narrow process into the temporal fossa before the occipital arch; in the camel it is narrower, and bears a longitudinal crest; and in the ox and antelope bubalus it is placed behind the occipital crest, and resembles a fillet surrounding the back of the head transversely. In the Solidungula the single parietal is nearly quadrilateral, and placed before the occipital crest.

The occipital bone in the lower mammalia is remarkable for five characters. 1. The proper occipital surface, instead of being oblique or horizontal, and inferior or basilar, becomes vertical and posterior. 2. The plane of the occipital hole forms with that of the orbits an angle constantly diminishing, becomes parallel to the orbital plane, and at length crosses it above the head. 3. The plane of the occipital condyles, instead of being transverse and horizontal, becomes oblique, and at length vertical. 4. The basilar or cuneiform process is not only horizontal, but forms with the occipital a right angle. And, 5. The mastoid process, which in man and the ape forms part of the temporal, belongs in the other mammalia to the occipital. In the polar bear, however, the mastoid process constitutes part of the temporal bone.

From the 1st, 2d, and 3d characters, it results that the head of quadrupeds is not balanced on the spine, but is suspended by muscles, tendons, and ligaments, especially the strong cervical, which connects the occipital spine to the spinous processes of the cervical and dorsal vertebrae. This ligament, therefore, though feeble and indistinct in man, is strong, particularly in quadrupeds with heavy head or long neck, in order to counteract the disadvantage of the long lever. It is strongest in the elephant, and is almost wholly ossified in the mole—a condition requisite for the burrowing faculty exercised by that animal.

The temporal bone is naturally distinguished in the Mammalia into two parts; a flat or proper temporal, corresponding to the squamous part of the human temporal bone, and the pyramidal, acoustic, or auditory, corresponding to the pyramidal or lithoid portion of the human subject. The first only, which is proper to the skull, claims attention here. In the orang-outang and most of the genus simia it forms a trapezium with the longest side above, and the height of which varies with that of the skull. In the American apes it is smallest in this direction. In the Zoophaga the proper temporal bone is as in the ape. Being narrow in the Rodentia behind, it is a little rounded in the short-muzzled Edentata, the Ruminantia, and Pachydermata.

The ethmoid is, strictly speaking, the olfactory bone, and shall be mentioned under the organs of sense. The sphenoid, among other offices, may be regarded as the essential ophthalmic bone.

The facial bones of the lower Mammalia differ from those of man; first, in the number of separate pieces; and, secondly, in the form and proportional horizontal extent.

The difference in number consists in each superior maxillary bone being divided into a maxillary bone proper, and an anterior or labial portion; which being interposed between the proper maxillary, are commonly denominated the intermaxillary (ossa intermaxillaria). As it bears also the superior incisors, it is named by Haller the incisive bone (os incisivum); but since it is found not only in the ruminants, which, excepting the camel, are void of incisors, but in the Edentata and Cetacea, this denomination is less applicable than the former. It may be doubted whether these should be regarded as additional bones, as they are generally represented by zootomists; for they are in truth merely the incisive or anterior portion of the superior maxillary bones. In other respects, the difference between the human and the animal superior maxillary bone is, that in the former each bone is in one piece, in the latter it is in two. Even in the human fetus the trace of the separation may be recognised; and we have seen it in the human skull some years after birth. Conversely, it is early obliterated in some quadrupeds. Thus, though distinct in the orang-outang seen by Cuvier, it was not found by Tyson or Daubenton, and is wanting in one preserved in the Hunterian museum. In a young specimen of the jocko also, noticed by Cuvier, no trace of the intermaxillary suture was observed. It appears also to be wanting in the perforated bat, the horse-shoe bat, and the three-toed sloth.

Mutually united on the mesial plane, the intermaxillary bones are united to the maxillary by sutures, which pass from the outer angles of the latter, near the incisive holes, towards the palate, where they intersect. In form and size it varies in the different orders and genera. Small in many of the Zoophaga and the walrus, it is large in the Rodentia, in the hippopotamus, porpoise, and cachalot, and prominent in the wombat. In the duckbill it consists of two unciform portions, united by a broad intermediate cartilage.

The peculiarity of the animal face consists in the horizontal elongation of the two jaw-bones. In the monkey of the tribe this elongation is trifling; and all that is remarked is, that the palate and maxillary bones are more elongated in proportion to their height, and that their anterior part, instead of being vertical, is more or less inclined forwards. The degree of this elongation, which differs in different genera, may be estimated by the acuteness of the facial angle.

The narrowness of the interorbital space is another interesting character of the animal countenance. In the guenon and tal region, American ape it is a mere septum; but in the orang-outang, magot, and howler, it is larger, by reason of the nasal fossae ascending to this height. From these the face of the Zoophaga is distinguished by the following circumstances. 1. The breadth of the ascending maxillary processes throws the orbits to the sides; 2. these orbital surfaces form the anterior wall instead of the floor of the orbit; 3. the malar bone is united neither to the frontal nor to the sphenoid bone, and forms only the zygomatic arch and the lower margin of the orbit; 4. the orbit, closed neither behind nor below, communicates freely with the temporal fossa; and, 5. the palate bones are much elongated and form a considerable space of the internal wall, to which the ethmoid bone does not contribute. In the Rodentia the interorbital space is still larger, by reason of the size of the intermaxillary bones throwing the maxillary backwards and to the sides, where they form the inner orbital wall, in which the palate bones occupy only a small space. The anterior wall is formed by a process of the maxillary, which contributes to form the zygomatic arch, while the malar is suspended in the middle between the process and that of the temporal bone. Very similar is the face of the elephant, except that the height of the aleoeli from the tusks, thrusting the nose upwards, and shortening its bones, alters entirely the expression of the head of this animal.

In the sloth, in which the face is short in proportion to Comparative Anatomy.

The skull, the malar bone attached to the maxillary only, is not united to the zygomatic process of the temporal. In the long-nosed Edentata, in which the face is conoidal, the maxillary bones extend to the orbits, and are separated by a broad lacrimal bone, while a long palate bone forms the inner wall of these fossae. The zygomatic arch, which is interrupted in the ant-eater and pangolin, is completed in the Cape ant-eater and the armadillo. In the tapir and rhinoceros the maxillary bone passes beneath the orbit; and the nasal bones form a sort of vault, which supports in the first animal the trunk, and in the second the horn.

In the Cetacea the maxillary and intermaxillary bones form a sort of flattened beak, distinguished into four parallel bands, of which the maxillary, which are external, alone bear teeth in three genera, provided with the latter organs. The nasal fossa is a vertical opening before the cranium, surrounded before and laterally by the intermaxillary bones. The maxillary ascend in the same manner, and cover that part of the frontal bone which forms the orbital vault, but do not themselves contribute to the formation of this cavity. The nasal bones are two minute tubercles implanted on the frontal bone above the narrow aperture. The malar is in the shape of a style, suspended by cartilages beneath the orbit; and the latter cavity is completed behind by a process of the frontal, which joins the zygomatic of the temporal bone, and below which the orbital and temporal fossae communicate.

The direction of the orbits, the shape of their base or facial border, and their relation to the temporal fossae, are important circumstances in the animal face and cranium. In the simiae the angle of the orbital axes is rather smaller; and the shape of the margin, which is quadrilateral in the jocko, becomes oval in the ourang-outang and American monkeys. The angle of the axes enlarges in the other Mammalia; and the base or anterior margin becomes nearly circular in the Zoophaga, Rodentia, Edentata, and Pachydermata; but the arch is incomplete behind. In the Ruminants and Solidipeda, however, in which it is also circular, the border is complete. In the Cetacea the orbital vault is semicircular, their axes are rectilineal, and there is no floor.

In the human skull the junction of the malar bone with the frontal and sphenoid completes the orbit externally, and prevents it from communicating with the temporal fossa; and the same arrangement is observed in the simiae. In the Carnivora, Rodentia, Edentata, and Pachydermata, however, in which the malar bone is united neither to the frontal nor the sphenoid, the orbit is not only incomplete on the external posterior border, but communicates freely with the temporal fossa. In the Ruminants is observed an arrangement intermediate between that of the Quadrumania and that of the Carnivora. The malar bone, united to the frontal, completes the orbital ring; but as it is not united to the sphenoid, it allows the orbits and temporal fossae to communicate. The orbit of the mole is so superficial, that it can scarcely be said to exist.

The lower jaw of the mammiferous quadruped differs from that of man chiefly by the following circumstances. The triangular flat surface which constitutes the chin, and which is most distinct in the Caucasian race, begins to become faint in the negro, and is altogether lost in the monkey tribe. In the ourang-outang, indeed, the animal character of the lower jaw appears distinct in the vertical convexity of the anterior arch of the jaw, and the retreating of its lower margin. In the lower Quadrumania the anterior maxillary arch is still more retreating, and the maxillary ramus form a more acute and elongated angle. These animal characters are still more conspicuous in the Car-

Nivora, most of the Pachydermata, Ruminants, Soli- dipeda, and Rodentia. The ascending ramus also becomes short in the Pachydermata and several of the Cetacea, more so in the Zoophaga, and is almost extinct in several of the Rodentia, for instance the pacas, beaver, and porcupine, and the armadillo, ant-eater, and duck- bill, among the Edentata. In the Zoophaga, however, in which the prehensile and masticatory muscles are large and powerful, the ramus becomes broad, and its coronoid process is extensive. The angle which the ramus forms with the body of the jaw, and which is almost right in the adult human subject, becomes obtuse in the lower ani- mals, nearly at the same rate at which the ramus dis- appears; and indeed the transition of the angle into a straight line implies the disappearance of the ramus. This, therefore, is the character in the Edentata and Ceta- cea, in which there is neither ramus nor coronoid process, after these parts have been seen for the last time in the amphibious Mammalia.

When the mammiferous cranium is considered gene- rally, and the relative direction and proportion of the cranial and facial part of the head examined, we recog- nise more distinctly the characters by which the lower orders of that class are distinguished from man. This character consists in the position of the occipital bone and hole, the position and direction of the facial bones in re- lation to the frontal, the elongation of the former, and large size which they present in relation to the cranial.

In the human subject, it has been already observed, the position of the occipital bone is oblique and horizontal, and the plane of the occipital hole is horizontal, while its position is anterior. In most quadrupeds, while the bone assumes a vertical position, the hole becomes posterior, and its plane vertical or oblique, in proportion as the face is elongated. The plane of the occipital hole forms with that of the horizontal a considerable angle, which Dauben- ton undertook to determine, by drawing one line through the plane of the aperture, and another from its posterior margin through the lower edge of the orbit. (Mém. de l'Acad. des Sciences de Paris, 1764, p. 568.) In the horse this angle is about 90°, while in the ourang-outang it is only 37°, and in the lemur 47°. In other respects, however, it furnishes an imperfect result, since in most quadrupeds which differ very much it ranges between 80° and 90°.

The direction of the face in relation to that of the Camperian cranium, determined according to the method of Camper, line and furnishes more accurate results. While in the human angle subject it varies, according to the races, from 70° to 80°, in the ourang-outang it is only 65°; in the American and long-tailed monkeys about 60°; in the macaca and baboon about 45°; and, lastly, in the mandrill, the most vicious and ferocious of the monkey tribe, only 30°. In some species in which the car is elevated and the guttu- ral fossa deep, for instance in the pongos and alonate or lowler, the small size of this angle does not indicate pro- portional elongation of muzzle; and to rectify this incon- venience, it is requisite to draw the basilar line of the facial angle parallel to the base of the nostrils. With this modification, however, the Camperian line admits of correct application to the human race and Quadrumania only, in which the frontal sinuses are small and not promi- nent. In quadrupeds, for instance the carnivora, several of the ruminants, and in the elephant, the frontal sinuses are so large and prominent as to affect the results given by the facial angle very materially. In other orders, again, for instance the Rodentia and the mouse, the nose occupies so much space that the cranium is inclined backwards without its walls being free before; and it is impossible to know where the facial line passes. These, therefore, must be measured by the inner surface. Lastly, Comparative Anatomy.

In the Cetacea the pyramidal elevation of the cranium above an elongated but flattened face renders the facial line much more vertical than it ought to be. The following measurements show the angle subtended by a line drawn parallel to the base of the nostrils, and another passing by the anterior margin of the alveoli, and touching the convexity of the cranium, whether the point of contact be concealed by the face or not.

| European infant | 56* | Mastiff, tangent within | 31 | |-----------------|-----|------------------------|---| | European adult | 65 | Hyena, without | 49 | | European aged | 75 | Ditto, within | 23 | | Negro adult | 70 | Leopold, within | 28 | | Young orang-outang | 65 | Hare, within | 26 | | American monkey | 65 | Marmosette, within | 25 | | Java monkey | 57 | Porcupine | 23 | | Young mandrill | 42 | Pangolin | 39 | | Coati | 28 | Babaroussa | 29 | | Pole-cat | 31 | Ram | 30 | | Pug-dog | 35 | Horse | 23 | | Mastiff, tangent without | 41 | Dolphin | 25 |

Method of Cuvier.

Aware of the imperfect results obtained in this method of measurement, Cuvier proposes to estimate the relative proportion of the cranial and facial part of the head, by comparing the respective areas exhibited by a longitudinal and vertical section of both. In this section the area of the cranium is to that of the face sometimes in a ratio of majority, sometimes of minority, occasionally of equality.

In the European the area of the cranial section is about four times that of the face, excluding that of the lower jaw. In the negro the cranial area remaining the same, that of the face augments about one fifth, whereas in the Calmuck it augments only one tenth. In the orang-outang the proportion is still less. In the American ape the facial is almost half the cranial area. The ratio is that of equality in the mandrill and most of the Carnivora, except the varieties of short-muzzled dogs, as the pug, in which the facial is rather less than the cranial area.

In the Rodentia, Pachydermata, Ruminants, and Solodungula, the facial is larger than the cranial area. Among the Rodentia, in the hare and marmot, it is a third larger; in the hedgehog double; in the Ruminants almost double; in the pig a little more than double; nearly triple in the hippopotamus; and almost four times in the horse. In the horse and elephant the face is rendered large by the height of the alveoli; and it may be regarded as augmenting the organs of the senses. The cranium of the Cetacea is very convex, and the face very flat, and the proportional area of the latter is thereby diminished. The facial area of the dolphin may be a third larger than the cranial.

The outline of the cranial section in the human subject is oval, that of the facial section forms a triangle, with the longest side contiguous to the cranium, and the smallest without, while the angle formed by the latter with the third side or palate is the facial. In the lower animals, this triangle, which may be named the facial, becomes so much elongated, that the cranial side, which is the longest in man, becomes the shortest of the three in the cynocephalus and mandrill, and continues so in the other quadrupeds.

The pelvis (pelvis) of the Mammalia in general agrees with that of man in forming a part common to the trunk and the lower extremities. It differs, however, altogether in the direction which it takes, which is obliquely backwards, with its anterior opening or brim forwards and downwards, and in the bones being smaller and much narrower; both of which characters are connected with its not being used in the lower animals to oppose the gravitating weight of the abdominal and pelvic viscera. In the apes, most similar to man, the coxal bones are much elongated; and in the Zoophaga, their superior or ilial part is not much broader than their pubal. In the Rumianta, the Pachydermata, and Solodungula, the ilial portions again become broad; and in the elephant and rhinoceros especially, this width, combined with the length of the ilio-pubal rami and the concave abdominal surface, concurs to give the pelvis of these animals the prodigious capacity by which they are distinguished. The pelvis of the amphibious Mammalia differs from that of the Zoophaga only in being narrow and elongated, and in the pubis being thrown behind. In the ant-eater, mole, and shrew, the pubal junction is open as in birds; and in the two latter genera, the bones are so narrow that the sexual and urinary organs are placed without its circumference. In the sloth genera, e.g., the Ai and Uman, the pelvis is wide, the cotyloid cavities turned upwards, and the ischial tuberosity is united with the sacrum, so as to convert the ischiatic notch into a hole. This sacro-ischial junction is also observed in others of the Edentata, as the ant-eater and armadillo, and in the phascoloma (didelphis urina). The marsupial animals present two minute bones, one on each side, connected by movable articulation to the pubis, and which are employed to sustain the mammary pouch (marsupium) or nipple-bag, in which the young are reared after exclusion from the uterus. These bones, which are distinguished by the name of marsupial (ossa marsupialis), are oblong and flattened. Lastly, in the Cetacea, in which the pelvic extremities are wanting (Plate XXXIV. fig. 2), the pelvis is also so far deficient, that instead of consisting of the sacrum and coxal bones, it is represented by a small bony appendage, suspended in the soft parts on each side of the anus, and which, meeting at angles on the mesial plane so as to form a bone like the letter V, are merely a rudiment of the ischial bones.

The shoulder of the Mammalia generally differs from that of man by the absence or the proportions of the collar-bone, and by the shape of the scapula.

The collar-bone exists in the Quadrumania nearly as the collar-bone in man; but it is wholly wanting in the three orders of Ungulata—Pachydermata, the Ruminants, and the Solodungula—and in all the Cetacea. Between these extremes it is found in various forms in the intermediate orders of the Ungulata. Among the Zoophaga it exists in the Chiroptera, especially the bats proper, in which it is strong and large; the Insectivora, as the hedgehog, shrew, and mole genera; and in the didelphis or opossum among the marsupial animals. In the others of this order, as the bear, raccoon, coati, weasel, otter, dog, cat, and seal, the collar-bone is represented by clavicular bones, suspended among the muscles, touching neither the sternum nor acromion; and in some species it is altogether wanting. The Rodentia may be distinguished into two subdivisions, as they are provided with or void of collar-bones. The first comprehends the squirrel, beaver, and mouse, with the helams, marmot, and ayu-aye or cheiromys genera. The second consists of the porcupine, hare, and cavy genera, as the guinea-pig and paca, in which the collar-bone is rudimental only, suspended among the soft parts. It exists in most of the Edentata, as the sloth, armadillo, ant-eater, and the gigantic fossil animal named megatherium; but it is wanting in the pangolin, and was believed to be wanting in the echidna and duckbill till Cuvier demonstrated its existence. In the Cetacea there is no vestige of collar-bone.

From these facts it results that the clavicle exists in all animals, the fore legs of which are frequently or habitually protruded, either to seize, as apes and the Rodentia; or to fly, as bats; or to dig and burrow, as the mole; or to rake the ground, as the hedgehog and ant-eater. In the mole particularly, the collar-bone, instead of being long, is Comparative Anatomy.

A broad, thick, short, quadrangular bone; and while it is connected to the acromion by a ligament, it is articulated to the humerus by a large facet. The collar-bone of the echidna and ornithorhynchus is very singular. It consists of a broad central bone, surmounted by two transverse branches spreading out on each side, so as to give the whole bone some resemblance to the letter T, but situated so as to make the diverging branches like the Greek υ. In young animals this bone consists of three portions. The two diverging branches are genuine collar-bones, and may be regarded as a bifurcated bone; while the middle is supported on the sternum, and has articulated to each side a part of the scapula, corresponding to the coracoid process. The collar-bone, indeed, is a powerful buttress, which prevents the arm-bone from being thrust too much forward.

Of the shoulder-blade or scapula, which is present in all red-blooded animals with thoracic extremities, and hence in all the Mammalia, the principal point is to remark the varieties which its shape presents. Though in man, most of the Quadrupeds, the Chiroptera, and the elephant, the vertebral margin or base of several authors on human anatomy is the longest, it becomes the shortest in most quadrupeds, especially those which, like the Ruminants and the Solidungula, have long legs and narrow chest. In most of them, also, this margin, instead of being straight, is rounded, as in the Carnivora and Rodentia. In the Carnivora without collar-bone, the hedgehog and didelphis, the acromion is less prominent; there is another eminence directed backwards, almost perpendicular to the spine. The coracoid process, also, which is present in the Chiroptera, the hedgehog, and didelphis genus, is wanting in most of the zoophagous tribe. In the hare the acromion terminates in a long slender process, rising at right angles and bending backwards, which may be named the recurvatum. In the Ruminants and Solidungula, not only are this and the acromion, but even the coracoid, wanting. The scapula, again, of the hog and rhinoceros is remarkable for the disappearance of the spine at the glenoid angle; while from its middle proceeds a prominent process towards the costal or inferior margin. In the mole the scapula is long and narrow, like a cylindrical bone, placed parallel to the spine,—an arrangement which, together with the shortness and thickness of the clavicle, already mentioned, is evidently connected with the burrowing habits of this animal. Lastly, in the echidna and ornithorhynchus, which in so many characters of organization approach the Amphibia on the one side, and the Birds on the other, the scapula is a single sinuous bone, attached by one extremity to the sternum and middle part of the clavicular bone, with the other loose; and in the middle an articular cavity, in which the head of the humerus is placed, and which evidently corresponds to the glenoid. In this instance, therefore, the clavicle and scapula may be regarded as united into a single bone.

The humerus, which exists in all the animals with thoracic extremities, undergoes considerable variations. In the lower animals generally it is much shorter than in man; and it is invariably shorter in proportion as the metacarpus is elongated. Thus, in animals with what is named a cannon bone, that is, one metacarpal, as in the horse and the ruminants, the humerus is so short that it is concealed in the soft parts as far as the cubit. In the Cetacea it may be said to attain its maximum of brevity. In the bat and sloth it is long in proportion to the rest of the body.

The humerus of the mole is perhaps the most extraordinary of all those of the mammiferous animals. Not only is it articulated with the scapula by a small head, but it is connected with a facette of the clavicle by another belonging to the great tuberosity, and between which and the head is a deep pit. The crest of the small tuberosity Comparative Anatomy is so large, that it represents a square placed vertically, so that the linea aspera is above. The rest of the anatomy of the bone, which is very short, is arched above, so that the cubital extremity is directed upwards. From this arrangement it results that the cubit is elevated above the shoulder while the palm is turned downwards,—a disposition necessary for the burrowing habits of the animal.

In the simiae the radius and ulna are arranged as in Radius and man, except that in the cynocephalus, mandrill, magot, and guenon, the coronoid process of the ulna is narrower, and the radial facet deeper. In the other Mammalia the ulna very generally disappears or becomes rudimentary only. In the bat family and the colugo (galeopitheca) the ulna is wanting or is represented by a slender style placed below the radius. These animals are therefore destitute of the power of pronation and supination. In the Zoophaga, the radius and ulna, though separate, are void of rotary motion; and the olecranon is compressed, and continued farther back than in man. In the Pachydermata the radius is before and the ulna behind, and, though distinct, there is no rotation. In several of the Rodentia, for instance the marmot, porcupine, &c., the coronoid process is small, and in others, e.g. the cavy, hare, and mouse family, it is altogether effaced. In the Ruminants the ulna is united immovably to the radius; and in the Solidungula it is represented by an olecranon adhering to the posterior surface of that bone. In the Cetacea, though both bones are present, they are much flattened.

The carpus of the ape genus contains one bone more Carpus than that of man, situate between the pyramidal and large bone, and which seems to result from the trapezium being divided into two parts. Conversely, in the Zoophaga, but especially in the dog, cat, hedgehog, shrew, bear, and seal, the scaphoid and semilunar are united into one large bone. Those which have a vestige of thumb, as the hyena and glutton, have the trapezium very small. The mole has not only 9 carpal bones, as the ape, but a large sickle-shaped bone, which is attached to the radial margin of the fore paw, and which gives it the shape proper to the habits of the animal. The toes are further very short. Of the Rodentia, the hare resembles the ape; but in the beaver, marmot, squirrel, and cat, the scaphoid and semilunar make one bone; while in the porcupine the supernumerary bone is between the pisiform and metacarpal of the fifth toe. In the two-toed ant-eater there are only 6 carpal bones, 4 in the first row and two in the second; in the three-toed sloth there are only 5, 3 in the first row and 2 in the second; the pangolin has 7; the cachecame 8 and a rudimental small toe; the elephant 8, 7 wedge-shaped and one elongated, corresponding to the pisiform; and the other Pachydermata 8. In the rhinoceros, which has only 3 toes, the trapezium only is wanting; but there is a supernumerary bone on the margin of the scaphoid, and on that of the unciform, as in the porcupine. The first range consists, in the Ruminants and Solidungula, of 4 bones; in the former, excepting the camel, the second consists of 2, and the latter of 3. Those of the Cetacea, which are much flattened, are 3 in the first row and 2 in the second.

The Mammalia generally have as many metacarpal Metacarp bones as toes, that is, never fewer than 3 or more than 5, with the exception of the Ruminants, in which these bones are in early life consolidated into one named the cannon bone. In animals which walk on the tips of the toes, or which use them as organs of prehension, the metacarpal bones are lengthened to nearly double; and hence in all these animals the metacarpus is erroneously named the fore leg, and therefore it has been imagined, that in several Comparatively of our domestic animals the different parts of the lower extremity are articulated in opposite directions to those of man. Thus the fore leg of the horse, deer, sheep, and dog are in truth the metacarpus of these animals; and what is vulgarly named the fore knee or cannon bone of the horse, is actually the carpus or wrist-joint. It is therefore convex on the dorsal, and concave and inflected on the palmar aspect, exactly as the carpus of the human subject.

In the three-toed sloth, the three bones of which the metacarpus consists are mutually consolidated at the base and with the rudiment of a fourth toe. In the Cetacea, the metacarpal bones, which are much flattened, are also mutually united.

Fore toes. In the Mammalia generally, if we include imperfect or rudimental phalanges concealed in the skin, there are never fewer than 3, nor more than 5. The Ungulata generally have 5, perfect and imperfect. The character of the perfect fore toe or finger is to consist of 3 rows or phalanges, excepting the first of the radial side, which has only 2. In the Quadrupedata this is separate, and opposable to the other toes, constituting a thumb, and giving this tribe of animals a prehensile organ entitled to the epithet of hand. It is, however, shorter and less perfect in other respects than the genuine thumb of the human hand. In the coatis (simia paniscus) it is converted into a rudimental bone, concealed under the skin.

In the Zoophaga, which have no power of grasping minute objects, the thumb or first toe is parallel to the others, and, though equal in length to these in the ursine family, it is shorter in the martela, virella, canine and feline genera. In the latter, which have the power of erecting the claws, to prevent them from being blunted in walking, the shape of the middle and ungual phalanx is remarkable. The former is triangular prismatic, with two lateral and a plantar or palmar inferior surface. The third or ungual phalanx is shaped like a hook, consisting of two parts. One, directed forwards, sharp and pointed, receives the nail or claw, in a long groove like a sheath. The second part of the hook, which is behind, rises vertically from the lower part by which it is articulated, and is produced into two processes, to which are attached the erecting muscles of the claw, which are flexors of the phalanx.

Among the Rodentia there is a perfect but short thumb in the hare, beaver, and jerboa; a two-phalanx but concealed one in the squirrel, mouse, and rat family, porcupine, paca, agouti; and a one-phalanx concealed one in the cavy, guinea-pig, marmot, &c. In the Edentata the number of fore toes varies much; in the Tamarins, and Tamanindus or four-toed ant-eater, the thumb-toe is obliterated; in the Ai or three-toed sloth, both that and the fifth toe are obliterated; and in the two-toed ant-eater, and Unau or two-toed sloth, these, with the second toe also, are obliterated.

The elephant has 5 perfect toes, all concealed under the thick, callous hide of the foot. In hoofed animals with 4 toes, for instance the hog, tapir, and hippopotamus, the thumb-toe is in the shape of a small rudimental bone.

In the Ruminants the single metacarpal bone (Cheselden's figure of the Deer, Plate L) is articulated with two digital phalanges, which constitute one of the distinguishing characters of this order—the cloven foot. In some genera, at the root of these two perfect toes are two small bones, often covered with horn, which represent two other toes. The last or ungual phalanx is always trilateral in shape. In the horse and the Solidungula generally, the two lateral toes are represented only by two bony styles, named the splint bones, situate on the two sides of the metacarpal or cannon bone. The three phalanges of the single toe which constitutes the foot are distinguished as the pastern bone, which is the first phalanx; the corona, which is the middle or second; and the coffin bone, which is the third or ungual phalanx, which has the shape of the hoof, rounded before, convex above, and flat below. To the back of the pastern joint are connected two sesamoid bones; and to the coffin bone is attached another, named the shuttle bone. In the Cetacea, all the phalanges, which are flattened, and often cartilaginous, are united in the fin or paddle.

The thigh-bone, which is single in all the classes, follows the type of that of the human frame in general figure bone and parts. In the Mammalia it is, however, proportionally shorter, and its length diminishes as that of the metatarsus augments. In the Ruminants and Solidungula, for instance, it is so short that it is concealed by muscles against the belly; and hence it is too often overlooked and confounded with the leg. In other respects the general characters are, that it is not arched; that, excepting in the bear and some of the simia genus, e.g. the orangutan, it is shorter than the leg-bones; that its neck is very short, and more perpendicular to the axis of the diaphysis than in man; and that the great trochanter is raised above the head, which is directed inwards. In the simia it is quite cylindrical, and void of linea aspera. In the taper the middle part is found flattened; and at the external margin there is a prominent crest, terminating in an unciform process. In the rhinoceros the great trochanter and the unciform process are so elongated as to unite almost, and form a hole between them and the diaphysis. The unciform process is observed also in the horse, beaver, and armadillo. The thigh-bone of the seal is so short, that the half of its length consists of the two articular extremities.

Though the leg-bones of the Mammalia bear a general similitude to those of man, the tibia alone is constant; and the fibula, after becoming unusually slender, and changing its position from the outside to the posterior part of the tibia, is converted into a mere appendage, and at length disappears entirely. Thus, though it is distinct, and occupies its usual position in the simia, in the Chiroptera it is extremely slender; and since the femora are directed backward, the fibulae are turned towards each other. In several of the Edentata, for instance the phatagin, armadillo, and sloth, it is large, curved, and remote from the tibia. In the dog family and the Rodentia it is altogether behind the tibia. In the mole and murine genus it is consolidated to the lower third of the tibia, leaving an empty triarticular space above. In the rhinoceros, elephant, and hog, the fibula is flattened and united to the whole length of the tibia. In the ruminants it is represented by a small bony appendage, placed on the outer margin of the astragalus, below the tibia, and forming the external or fibular ankle. Lastly, in the horse and Solidungula, the fibula is reduced to a styloid rudimental process, which is firmly consolidated in the adult animal to the upper part of the tibia.

Between the tarsus of man and that of the other Mammalia, the following are the principal differences.

In the simia the fibular facet of the astragalus is nearly vertical, and the tibial is very oblique; and the calcaneum wants the tuberosity, except in the pongos. In the ordinary bat family the calcaneum is elongated into a styloid process, concealed in the substance of the membranous ulniform expansions; but in the roussette (pteropus) the tuberosity projects beneath the foot.

In the Rodentia the calcaneum is produced considerably backwards, while the scaphoid, which consists of two parts, forms a tubercle on the sole. Among the Edentata the three-toed sloth is peculiar in having a tarsus, Comparative Anatomy.

Consisting of four bones only, the astragalus, calcaneum, and two cuneiform bones, the first of which is articulated not only with the tibia, fibula, and calcaneum, but with the large cuneiform bone, without any intermediate scaphoid bone. Its connection with the tibia is by means of a convex articular surface, which rolls on the external part of the tarsal end of the tibia. From this mode of articulation it results that the foot of the sloth admits neither of being elevated nor depressed, but simply of performing lateral motions of adduction and abduction, to which it owes the power of clasping the trunks of trees and climbing, but which renders progression difficult and laborious.

The hog has a scaphoid with three ordinary cuneiform bones, and a rudimental great-toe bone beneath the first. In the tapir and rhinoceros there are only two cuneiform bones. All the animals already enumerated have the same number of metatarsal bones as toes.

In the Ruminants the cuboid and scaphoid bones are united, unless in the camel, in which they are distinct. At the outer margin of the pulley of the astragalus is a bone which represents the lower head of the fibula, and which is farther articulated to the upper surface of the os calcis. In this side also there are only two cuneiform bones, which are united in the giraffe. The two metatarsal bones are always united, as in the metacarpus, into one, which forms a posterior cannon bone. The Solidungula resemble the camel in this, that the scaphoid is distinct from the cuboid bone, and that there are two cuneiform bones, while the peroneal rudiment and the corresponding articular surface of the calcaneum are wanting. The metacarpal are also consolidated into a single piece, named the hinder cannon bone, each side of which is provided with a minute bony style.

The toes of the Quadrupedata and the Marsupialia are longer than those of man; but the great toe is shorter than the others, and its metatarsal bone is susceptible of separation and opposition, as the thumb or thumb-toe of the hand. Hence Cuvier, in his first classification, distinguished the latter by the name of Pedigiana. The Aie-ae among the Rodentia appears to possess the same faculty. Among the Zoophaga the great toe remains always conjoined with and parallel to the others; and in the canine and feline genera it is obliterated. Among the Rodentia, that of the beaver is nearly equal to the other toes; those of the marmot, porcupine, and the murine genus, are shorter; in the paca it is almost obliterated; it is reduced to a single bone in the Cape gerboa; and the leporine genus have no trace of it. In the cavy, agouti, and guinea-pig, the great and small toes are each reduced to one bone. In the gerboa (mus jaculus) and alactaga (mus sagitta) the three middle metatarsal bones are united into a single one similar to the cannon bone of the Ruminants and Solidungula; and while the two lateral toes are distinct, though short, in the former animal, they are obliterated altogether in the latter.

Among the Edentata, the ant-eater, orycteropus, pangolin, and armadillo, have five toes, of which the great is the shortest in all. In the sloth the great and small toe are reduced to one small bone. The other metatarsal bones are united at their base. The toes have only two phalanges, of which the ungual are the largest.

In the subsequent families the metatarsal bones deserve particular attention. In the elephant and Pachydermata, their tarsal extremity has a flat surface, and the phalangeal consists of a convex tubercle, which presents below a prominent line in the middle of the bone. In the Solidungula this line is above and below both. In the Ruminants, in which the cannon bone consists of the two metatarsal bones, the line of union is represented by a deep line like the tract of a saw. The elephant has 5 perfect toes; the hog 4; the tapir and rhinoceros 3; the Comparative Anatomy.

Ruminants have two perfect toes on one metatarsal bone, and two small ones attached behind its base. The Solidungula have one perfect toe, and two imperfect, which are reduced to a single styloid bone. In these animals the body is supported in walking by the last or ungual phalanx alone; and hence the term foot is not of the same import as in the human subject and animals similarly constructed. While indeed man supports his person in progression on the os calcis and the posterior or metatarsal phalanges, in the other mammiferous animals the former bone touches not the ground, but is always elevated above it a considerable height. All the zoophagous or ungulicated animals, excepting the plantigrade, support themselves chiefly on the ungual and middle phalanges both of the fore and hind foot; and neither the posterior phalanges nor the calcaneum touch the ground, as is easily demonstrated on observing the gait of the hedgehog, dog, fox, cat, or similar individuals of the same family. The animals distinguished by the name of Plantigrade are believed to support themselves on the entire foot. But though the foot is certainly spread on the ground more freely than in those already mentioned, by the bear, glutton, badger, and others, it appears that not the heel, but the metatarsus, is allowed to touch the ground in progression. In the Ruminants and Solidungula, as already mentioned, the only part of the foot which is applied to the ground is the ungual phalanx; and it is well known that the horse supports himself on the plantar surface of the coffin bone only.

Lastly, in the Amphibious Mammals, while the extreme brevity of the humerus and femur unfit them for progression on land without extreme awkwardness and difficulty, the expanded shape and oblique position of the metacarpal bones and phalanges, the length of the tibia and fibula, and the greater length of the first and last than the middle metatarsal phalanges, all concur to give these animals great facility in swimming. (Cuvier, Ossemens Fossiles, tome v., partie i., septieme partie.) In the Cetacea, again, while the total want of pelvic extremities renders motion on land quite impracticable, the fin-like disposition of the metacarpus and metacarpal phalanges, with the great strength of the lumbar, and the length of the coccygeal vertebrae, peculiarly qualify them for locomotion in the waters.

SECT. II.—Osteology of Birds.

Plate XXXIV.

The number of vertebrae of which the different regions of the spine consist, is not less variable in Birds than in the Mammalia. Some idea of these variations may be formed from the number exhibited in the following table by Cuvier.

| Species | Vertebrae of Neck | Vertebrae of Back | Sacral Vertebrae | Coccygeal Vertebrae | |------------------|-------------------|-------------------|------------------|---------------------| | Vultur. Vulture | 13 | 7 | 11 | 7 | | Falco fulvus. Eagle | 13 | 8 | 17 | 8 | | halisetus. Bald buzzard | 14 | 8 | 11 | 7 | | buteo. Buzzard | 11 | 7 | 10 | 8 | | sisus. Sparrow hawk | 11 | 8 | 11 | 8 | | milvus. Kite | 12 | 8 | 11 | 8 | | Strix albo. Eagle owl | 13 | 7 | 12 | 8 | | Strix alba. Brown owl | 11 | 8 | 11 | 8 | | Muscicapa grisea. Fly-catcher | 10 | 8 | 10 | 8 | | Turdus merula. Blackbird | 11 | 8 | 10 | 7 | | Tannagra tatao. Tanager | 10 | 8 | 9 | 7 | | Corvus corona. Crow | 13 | 8 | 13 | 7 | | —— pica. Magpie | 13 | 8 | 13 | 7 | | —— glandarius. Jay | 12 | 7 | 11 | 8 | | Sturnus vulgaris. Starling | 10 | 8 | 10 | 9 | | Loxia coecullans. Grosbeak | 10 | 7 | 12 | 7 | | pyrrhula. Bullfinch | 10 | 6 | 11 | 6 |

Spine. In this table the most remarkable circumstance is the great number of cervical vertebrae, which are much more numerous than in the Mammalia. They vary from 9, the number in the sparrow, to 23, which is that of the cervical vertebrae of the swan. The most common number is 11, which is that of 10 genera. The next most frequent is 12, 13, and 14, which are equally the numbers of 9 genera. The next is 15, which is that of 8; 10 occurs in 6, 18 in 4, and 16 in 3. In the stork and crane they are 19.

The next remarkable circumstance is, that the dorsal or costal vertebrae are greatly fewer than in the Mammalia, never exceeding the number of 11, and being more frequently about 7 or 8. Thus, while they are 11 in the cassowary, swan, and sheldrake, 10 in the goose, barnacle, and grebe, and 9 in the sparrow, lark, humming-bird, parrot, crane, avoset, oyster-catcher, cormorant, and black-diver, they are 7 or 8 in all the other genera, and only 6 in the bullfinch.

There are no lumbar vertebrae strictly so named, for those which extend from the chest to the tail are consolidated into one piece with the iliac bones. The tail, which is short, consists of from 7 to 9 vertebrae.

The part most variable in proportional length is the neck. It is so much longer as the feet are elevated, except in some of the swimmers, in which it is greatly longer, because they require to seek their food below the surface of the waters on which they float.

The bodies of the cervical vertebrae are articulated not by plane facettes, which would admit obscure motion only, but by portions of cylinders, which allow extensive motion. The 3d, 4th, or 5th superior vertebra allow of anterior inflection only, and the others of posterior inflection. This gives the necks of birds an alternate serpentine inflection; and it is by rendering the two arches, of which this curvature consists, straight or convex, that the animal elongates or shortens his neck. The articular processes of the superior vertebrae are directed upwards and downwards; those of the lower are turned anteriorly and posteriorly.

Instead of transverse processes, the cervical vertebrae of birds are provided with a tubercle above, and the anterior extremity of which terminates in a narrow style, descending parallel to the body of the vertebra.

Only the most superior and inferior vertebrae have distinct spinous processes, and these have anterior as well as posterior ones. The middle ones have before two crests, which form a half-canal, and behind a tubercle, often bifid, or, when they are elongated, two rough lines. The atlas, which is articulated with the occipital bone by a single facette, has the shape of a minute ring.

As the neck of birds is movable, the back is fixed. The back spinous processes of these vertebrae are in mutual contact, and they are connected by strong ligaments. Most of these processes are generally consolidated into a single continuous crest, extending along the whole back. The extremities of the transverse processes terminate in two apices, one directed forwards, the other backwards; and occasionally they are consolidated into a continuous mass like the spinous. That this arrangement is requisite for the trunk to remain fixed during the violent motions which take place in flying, is rendered probable by the fact, that in birds which do not fly, as the ostrich and cassowary, the spinal column retains its mobility.

The last dorsal vertebrae are often placed on the crest of the iliac bones, and they are then united, as the lumbar, on the large piece of the iliac bones, from which it results that the number of vertebrae can often be estimated in no other mode than by that of the holes of the nerves which issue from the chord.

The caudal vertebrae are most numerous in the species Caudal which move the tail with most energy; for instance, the magpie and swallow. They have spinous processes below as well as above, and very long transverse processes. The last of all, to which the pinions are attached, is longest, and has the shape of a ploughshare or a compressed quoit. In the cassowary, which has no visible tail, the last bone is conical; in the peacock, on the contrary it has the shape of an oval plate, situate horizontally.

It was early observed by the original zoologist and tran-Cranium-veller Pierre Belon, that the crania of birds were void of sutures; and that in a few only were these lines of distinction into separate bones recognised. The explanation of this peculiarity is found in the history of the ossification of the head in young birds, which shows that the cranium consists at that period of separate bones, corresponding in number and situation to those of quadrupeds. Thus, there are two frontal bones, which are continued forwards to form the vault of the orbits; two small parietal bones behind the frontal; a temporal bone on each side of the skull; a sphenoid united to the occipital, even in subjects in which the other sutures are distinct; or a spheno-occipital bone, which is early united with the temporal.

These sutures, however, are distinctly seen only in Comparative Anatomy.

Young birds and those recently hatched; for the bones are very early united, and in the adult bird the cranial sutures are invariably obliterated. Thus, in the domestic fowl and turkey the skull is one piece; and the only trace of suture that remains is a linear depression in the middle of the frontal bone, indicating the original formation in two halves. In the recently hatched bird, also, the sphenoid is separated from the occipital bone by a transverse suture, extending from the one ear to the other. The occipital bone is at the same time a ring, consisting of four parts; a superior, two lateral, and an inferior which is small. The sphenoid, which forms the greater part of the base of the cranium, is nearly trilateral, with a small anterior process, to which the palatine arches are articulated. It has no pterygoid processes, and does not touch the posterior aperture of the nostrils. The temporal bone, though void of zygomatic process, has a pointed style, which contributes to form the posterior margin of the orbit. The frontal bone, after covering part of the cranium, is continued forwards in a broad, thin plate, which forms the vault of the orbits, while these cavities are separated by a thin vertical bony plate which descends at right angles from the frontal bone, and is connected behind with the sphenoid. The long eminences observed on the heads of the cassowary, curlew, pintado, and some species of hocco, are produced from this supraorbital part of the frontal bone; and their interior, which consists of loose diploë, communicates with that of the same bone.

The face in birds is rarely so firmly consolidated as the cranium. It is composed of two lacrymal bones, forming the anterior margins of the orbits, and united on the mesial plane; two nasal bones anterior to the lacrymal; two bones corresponding to the superior maxillary, and forming the external lateral parts of the upper half of the bill; two inter-maxillary bones; two anterior palate bones, corresponding to those of the Mammalia; two posterior palate bones corresponding to the pterygoid processes of the sphenoid; and the lower jaw a paraboloid bone, consisting of two rami united before, where they are covered by the horn of the lower half of the bill. Besides these, there is in the whole class an irregular-shaped bone, common to the cranium and lower jaw, and connecting these two together. This bone, which has been rather improperly named the square, quadrangular, or quadrilateral bone (os quadratum), consists of a body with curvilinear hollow margins, terminating in two elevated and rather pointed processes, one of which is connected with the cavity named tympanum, while the other, projecting into the orbit, affords attachment to several muscles. The anomalous character of this bone has perplexed several of the most distinguished zoologists; and while Geoffroy gives it the name of os tympano-styloideum, Spix considers it analogous to the annular process of the temporal bone, which in the human fetus is separate; and Carus regards it as representing the incas, to which it bears a remote resemblance in shape and in one of its connections.

Both maxillae are void of teeth; but the hard, horny matter of the bill covering the margins and extremities of each jaw, and constituting the mandibles (mandibula), is manifestly constructed to perform for Birds what teeth do for the Mammalia. But the most remarkable peculiarity of the facial bones of this class is, that the upper jaw admits of more or less motion. In the majority of instances this is effected by the jaw being united to the cranium by means of thin, flexible, elastic, bony plates; but in the parrot family the upper jaw is entirely distinct, and is connected by a proper articulation.

The base of the palatine surface of the upper jaw is divided into 4 branches, which diverge backwards. The two external ones, which correspond to the zygomatic arches of the Mammalia, and which are very slender, are articulated to the quadrangular bone which moves on the temporal before the ear. The two intermediate ones, which have been already stated to correspond to the pterygoid processes, and which are parallel, are placed beneath the septum of the orbits, and are articulated by their posterior extremities with a small bone, variable in shape, but named omoïd by Herissant, which is also articulated with the quadrilateral. From this arrangement results a singular species of broken lever, not dissimilar to the parallel joint of the piston and lever of the steam-engine, and the effect of which is, that whenever the lower jaw is depressed by its proper muscles, it necessarily causes the quadrilateral bone to perform a slight rotatory motion; in consequence of which, by means of the omoïd bone, the upper jaw is at the same time elevated on the elastic plates; and as soon as the lower jaw is raised, the elasticity of these plates forces down the superior one.

The upper jaw is immovable in a few instances only, and of these the edaio or rhinoceros bird is one.

The breast bone (sternum) is a trilateral, boat-shaped Sternum bone, concave internally, convex with a middle long- or breast-tudinal crest externally, with the base of the triangle above, and the apex, which is also incurved backwards, below. The middle longitudinal crest, which is occasionally named the keel (carina), is shaped something like a spherical triangle, with the broadest side above, the base before, and the apex behind; and its prominence forms large spaces on each side for the attachment of the pectoral and other muscles used in flight. In the male wild swan (anas cygnus), in some species of curlew, in the crane, and in the guinea-fowl, this crest forms a cavity for the reception of the windpipe. In the ostrich and cassowary, which do not fly, the sternum is void of crest, and is merely arched strongly.

The ribs, which rarely exceed 10 pairs, may be distinguished into sterno-vertebral and vertebral. Though the latter are generally before, they are sometimes also behind. The vertebral end terminates in two diverging processes, one of which is articulated with the vertebral body, the other with the transverse process. The sternal extremity consists of a bony process, which performs the part of the sterno-costal cartilages of the Mammalia by uniting the rib to the sternum. The ribs of birds, however, are further distinguished by presenting near their middle a flat long process, projecting from the rib backwards at an acute angle, and resting on the rib immediately below, so that each rib is supported not only on the vertebrae and sternum, or the vertebrae alone, but on the next rib below. These processes are obliterated in the lower ribs.

The coccyx bones constitute one piece with the sacrum Basin or lumbar vertebrae. The ischial portion is united with pelvis, the sacrum, and the ischiatric notch is converted into a hole. The part which corresponds to the os pubis of the Mammalia is not consolidated before so as to form a symphysis, but proceeding directly backwards, terminates in a styloid process, variable in length and slenderness. The only exception to this mode of structure occurs in the ostrich, in which the pubal bones are united below. The infra-pubal or oval hole is present in the whole class notwithstanding. It is worthy of remark, however, that in young birds this and the ischial aperture are still notches, in consequence of the deficient ossification of the parts.

The direction of the pelvis in birds is nearly that of the spine, that is, obliquely backwards, and deviating but little from the horizontal line.

The wings or thoracic extremities are connected to the trunk by three bones, the collar-bone or clavicle, the scapula, and the bifurcated bone. The collar-bones, which bone. are straight, strong, and cylindrical, are articulated by a large head with the anterior and lateral part of the sternum, in which its motion is rather limited. It forms before and laterally two short processes, one anterior-inferior and internal, articulated with the bifurcated bone; the other posterior-superior and external, uniting with the scapula, and forming a cavity, in which the head of the humerus is lodged.

The scapula is a long bone, flattened, but narrow, and slightly incurvated, with the convex side turned towards the spine, to which it is nearly parallel in position. The head or anterior extremity is thick and extensive, oblique from before backwards, and is articulated behind with the clavicle, before with the humerus. The free extremity is thin, flattened, and sharp. The whole bone is not dissimilar in shape to a scimitar.

Besides these, which Birds possess in common with the Mammalia, we find an azygos bone, situate on the mesial plane, denominated in ordinary language the Merry thought, and, from its shape, the fork-like or bifurcated bone. It consists of two long, rounded, converging branches, united at an acute angle, and forming a broad process, flat in the vertical direction, and by which it is articulated to the anterior extremity of the crest or carinated part of the breast-bone. To the posterior or free extremities of the divergent branches are articulated the humeral ends of the collar-bones, which are thus enabled to sustain the violent motions of the humerus during flight. The branches of the bifurcated bone are separate in the ostrich, and each is united with the clavicle and scapula of the same side, so that the three bones form only one, much flattened, and with a hole towards the sternal extremity. In the cassowary the bifurcated bone is reduced to a mere rudimental process at the inner margin of the head of the clavicle. From these facts it results, that the bifurcated bone is particularly useful in the energetic and continued efforts of the wings in flight, and not only serves to keep the clavicles apart, but, by lengthening the distance between the collar-bones and sternum, enables the animal to use a longer lever. It is freest, strongest, and most elastic in the birds which fly best. In birds which do not fly, and which use the wings merely to sustain the equilibrium, as the ostrich and cassowary, it is reduced to almost nothing, or it is in such a rudimental and imperfect form, that it cannot keep the collar-bones apart.

The bones of the thoracic extremities, or those of the wings, correspond in general to those of the Mammalia. They consist of a single cylindrical humerus, articulated with the scapula and collar-bone above, two bones of the fore wing corresponding to the ulna and radius, two bones of the carpals, two of the metacarpus, consolidated by their extremities, one styloid bone as a thumb, a long finger consisting of two phalanges, and a short one consisting of one. The thumb supports the bastard pinions, the large finger and metacarpus the primaries, while the small one, which is covered by the skin, is destitute. In several of the web-footed divers, for instance the duck and penguin (alca impennis and sphenocephalus), these bones are flattened like thin plates.

In the pelvic extremities the thigh-bone is provided with one trochanter only, is shorter than that of the leg, and is almost invariably straight; and is arched only in the cormorant, duck, and dabchick. In the ostrich its diameter is about four times that of the humerus. The tibia differs from that of the Mammalia chiefly at its lower extremity. While the fibula adheres to it like a slender appendage as far as the middle, the tarsal extremity terminates in two trochlear condyles, with an intermediate pulley-like groove. The tarsus and metatarsus are represented by a single bone of considerable length, and the comparative head or tibial end of which consists of a middle prominence and two lateral depressions, and which, therefore, moves in cardinal opposition, but does not admit of extension beyond the straight line. Though variable in proportion to the length in different orders, this bone is very long in the order Grallae (Grallatores). It terminates below in 3 pulley-shaped processes, to which are attached the bones of the 3 anterior toes, with an internal margin for that of the great toe. In the ostrich there are 2 processes only, corresponding to the two toes. In the penguin tribe, however, the tarsus and metatarsus consist of 3 bones, separate from each other in the middle, but united at the tibial and digital extremities. To the tarso-metatarsal bone of the cock, and others of the Gallinaceous tribe, is attached the spur, a conical pointed excrecence of hard horny matter.

SECT. III.—OSTEOLOGY OF THE REPTILES.

The number of vertebrae, and all the other attributes of the spinal column, vary more in this class than in all the others.

In the Cheloniad or Tortoise family there are 7 cervical, 8 dorsal, connected with the shell in an immovable piece, so as to have neither processes nor articular facettes; from 3 to 5 lumbar and sacral, consolidated in like manner; and about 20 caudal or coccygeal. (Plate XXXIV. fig. 5.)

In the Saurial or Lizard tribe, the number 7 predominates in the cervical, being that of the crocodile and most lizards. In several, however, there are 8, as in two of the monitor genus, the American safeguard, the lizard of Fontainebleau, the dragon, the iguana, the anolis, and the gecko and scinc; and in a few, as the Nilotic monitor, and an undetermined species of monitor, they amount to 9. In the chameleon there are only 5 cervical vertebrae. Here, however, a singular peculiarity is observed. Instead of the cervical vertebrae being, as in the Mammalia, distinguished by being unconnected with ribs, to those, from the third to the seventh inclusive, short ribs, unconnected with the sternum, are attached. The atlas and axis, therefore, alone are proper cervical vertebrae; but the general analogy is observed in the cervical ribs being exceedingly short and almost rudimental. The dorsal vary from 11, which is that of the crocodile and iguana, to 29 and 30, which are the numbers in the New Holland scinc and Nilotic monitor. In the American safeguard, cordylus, stellio, crested basilisk, dragon, guana, and great anolis, they are 16; in the chameleon, black safeguard, and ameiva, 17; in the tapinambis, spotted gecko, and golden scinc, 18; in the green lizard and spotted guana (polychirus) 19; in the Fontainebleau and gray lizard 20; 21 in the Levant scinc and undetermined monitor; and 22 in the Java and New Holland monitor.

The Batrachoid or Ranine reptiles are void of ribs, and it is impossible therefore to distinguish the first three orders of vertebrae from each other. In general, however, there are from the nape to the pelvis 8 vertebrae, all provided with long transverse processes, and which are longest in the last. The sacrum is represented by a long flattened but pointed bone, without coccyx. In the Surinam toad (rama pipa) the last vertebra is consolidated with this bone; and the transverse processes of the second and third vertebrae are so much larger than the others, that they resemble rudimental ribs. In the Salamander family there are from the head to the sacrum 14 vertebrae, all alike in shape except the first, which receives the occipital bone, and the last, which is articulated with the sacrum. These two are distinguished by wanting rudimental ribs, which are small elongated bones, movable, and articulated with the trans- Comparative Anatomy.

The articular processes which are directed backwards. The articular processes are large and imbricated, the posterior resting on the anterior, so as to resist the motion of the spine backwards. The sacrum consists of one vertebra only, but the coccyx or tail is composed of 27.

In the Serpentine tribe the vertebrae may be said to attain the most extensive numerical development. With the exception of the head and rudimental ribs, they constitute the whole skeleton. (Fig. 3.) From the head to the tail their shape is the same, and may be distinguished into body, articular and transverse spinous processes. In some species, for instance the boa, the spinous processes of the back are so much separated as to allow mutual motion to a considerable extent. In others, conversely, for instance the rattlesnake, these processes are so long and broad as to touch each other, while the oblique processes, which form their bases, are imbricated over each other. In consequence of this arrangement the motion of the spine is limited behind, but more extensive on the ventral surface. The vertebral bodies, which move easily on each other, are provided with a sharp spine directed towards the tail, which somewhat limits motion in this direction.

The first vertebra differs from those of the rest of the body in supporting short or rudimental ribs; there are therefore no cervical vertebrae and no proper neck in the serpentine family. The caudal vertebrae are distinguished by not supporting ribs, and by their spines both dorsal and ventral being double, and forming two rows of tubercles. The articulation of the bodies of these vertebrae is peculiar. On the anterior part of the body is a round hemispherical tubercle, while the posterior presents a corresponding cavity, so that each vertebra forms a cup and ball joint with the following one.

The number of costal vertebrae varies from 32, which is that of the blind worm (Anguis fragilis), to 204 in the ringed snake (Coluber natrix), 244 in the snake, and 252 in the Boa constrictor, and which is perhaps the greatest known number. Of intermediate numbers, the Amphibiania has 34, the viper (Crotalus horridus) has 139, the rattlesnake 175, and the cobra di capello 192. The caudal vertebrae vary in number from 7, which is that of the Amphibiania, to 112, which is that of the Coluber natrix. Of intermediate numbers, the blind worm has 17, the rattlesnake 26, the boa 52, the viper 55, and the cobra 63; from which it appears that the number of the caudal is not in proportion to that of the costal vertebrae.

Of the heads of the Cheloniads, the most remarkable characters are, that the facial line is horizontal, and quite continuous with the cranial line; that the orbits, though complete without, are continuous behind with the temporal fossa; that the parietal and occipital bones are compressed laterally, while the latter terminates above in a sharp spine, projecting behind. The occipito-parietal and occipito-temporal sutures are distinct. The cranial cavity is small compared with the volume of the skull.

These characters are not less remarkable in the Saurial or Lacertine Reptiles. The cranium of a crocodile measuring from 13 to 14 feet is scarcely capacious enough to admit the thumb; and Cuvier estimates the area of the cranial section, which is oblong, at about \( \frac{3}{4} \) of that of the whole head. In these animals, indeed, the bones of the superior and inferior jaws are so much prolonged, and occupy so large a proportion of the head, that small space is left for the proper cranial cavity, which indeed is an immediate continuation of the vertebral. In these animals, also, the anatomist can trace, much more distinctly than in the more perfect, the resemblance between the cranial bones and the vertebral. In the Cheloniads, and Saurial especially, the occipital bone is very distinctly a cephalic vertebra.

Still more manifest is this arrangement in the Ranine Comparative Anatomy of Batrachoid and Serpentine or Ophidian Reptiles. In the former, as exemplified in the frog, the occipital bone, which forms the posterior cranial vertebra, consists of four pieces, and has two articular processes. The middle cranial vertebra is represented by the parietal bones above and the posterior part of the sphenoid below, while between it and the occipital or posterior is contained the temporal as the organ of hearing. The third or anterior cranial vertebra is represented by the anterior part of the sphenoid bone below and the two narrow frontal bones above. The face, which may be regarded as the organ of the senses, is elongated anterior to the head, somewhat after the manner of the Cheloniad family; while an approximation to the Birds is indicated in the articulation of the lower jaw, which is connected to the head by the intervention of a quadrilateral bone.

In the Serpentine family, the cranium of which is very similar in other respects, the most remarkable deviation is in the want of ethmoid bone. The lower jaw is connected to the cranium by an intermediate bone, corresponding to the quadrilateral, but of an oblong shape, and something like a collar-bone.

The chest of the Reptile class varies much in the mode of formation. While true ribs are recognised in the Saurial family only, the Batrachoid reptiles have a sternum without ribs, the Serpentine ribs without sternum, and the Cheloniad ribs united into the dorsal shell, and a sternum expanded into the abdominal one.

In the Saurial family the ribs correspond in number to that of the costal vertebrae already mentioned, that is, 12 in the crocodile and iguana, two of which are not connected to the sternum, 17 in the chameleon, 18 in the tupinambis, and 27 in the monitor. The Saurial reptiles, however, are peculiar in having from 1 to 6 ribs attached to the cervical vertebrae, and the opposite ends of which are not connected to the sternum. These, which have been named cervical ribs, form a transition to the rudimental ribs of the Serpentine family, which are larger in the neck than elsewhere. The sternum of the crocodile consists of two parts,—an anterior or thoracic, which is osseous, supporting the two collar-bones,—and a posterior or abdominal, which is cartilaginous, and extends to the pubis, and furnishing to the abdominal parietes eight cylindrical cartilages. In the East India crocodile it appears that these lateral processes are converted into a single broad piece of cartilage on each side. (Fig. 4.)

The ribs of the Cheloniad family are represented by Dorsal and the dorsal shell, which consists of eight broad incurved sterno-abdominal plates, identified behind with the dorsal vertebrae, and terminating before in the margin of the shell, and which are doubtless genuine ribs. In the ordinary land-tortoise shell (Testudo Graeca) these are seen in the shape of elevated bony ridges, proceeding from the head of each rib in a transverse concave bend to the margin of the dorsal shell. On each side of these ridges the bone is depressed, and is united at its lowest point by a genuine suture with the adjoining ones. These sutures, however, are not continuous with those of the sterno-abdominal shell, but meet it in the intermediate points. (Fig. 5.) The sterno-abdominal shell consists, in like manner, of several transverse pieces consolidated into one. The ordinary number is eight on each side of the mesial plane, and a ninth azygous, generally placed in the centre of the shell. In a specimen, however, of the tabular tortoise (Testudo tabulata), in our possession, the number of the sterno-abdominal pieces is 11, of which 8 are in pairs, united on the mesial line from before backwards, and 3 azygous at the posterior tip of the shell. In young animals it is easy to recognise the unions of these constituent bones, which consist of sutures ex- Anatomy.

Comparatively similar to those of the cranium in the Mammalia. So feeble is the union, that it often happens that the abdominal shell especially separates at the lines of junction, in the attempt to detach it from the dorsal.

The Batrachoid Reptiles, though void of ribs, are provided with a sternum, which before is a cartilaginous process, terminating on a disc placed below the larynx, where it receives the collar-bones, and forms behind a broad plate placed below the abdomen, and giving attachment to the muscles. In the Salamander tribe, which are without sternum, the ribs consist of twelve pair of small rudimental processes, articulated with the vertebrae, but admitting of very limited motion.

Lastly, in the Serpentine family, though there is no sternum, the upper vertebrae are provided with costal processes, quite rudimental. The great number of these costal rudiments, amounting in the rattlesnake to 175, in the cobra di capello to 192, in the coluber natrix to 204, and in the boa constrictor to 252, and the freedom of their anterior extremities, enable the animals of this tribe, which are destitute of locomotive members, thoracic or abdominal, to employ the spinal column and the ribs as organs of progressive motion. On this point the reader will find some interesting observations by Sir Everard Home (Phil. Trans. 1812, p. 163). In the region of the neck, where the ribs acquire peculiar length, they are employed in erecting that region, and producing the expansive swelling peculiar to this tribe of animals. It is an important link in the same series of facts, that in the animal absurdly named the flying lizard (draco volans), the five posterior ribs are recurved and elongated to form the bony skeleton of the membranous sails by which the animal supports itself in its desultory flight from tree to tree.

It is in the Saurial family that the locomotive extremities of Reptiles ought first to be studied. In these we find an elongated scapula without spine, and one short flat bone, constituting the clavicle, united to the sternum. In the iguana and chameleon this bone is broad and nearly quadrilateral, while in the tuipambis it is large and oval-shaped, with its greatest length from before backwards, and with two unossified points.

In the Ranine tribe, while the scapula consists of two articulated pieces, the upper towards the spine, each shoulder is provided with two collar-bones attached to the two extremities of the sternum, and the two anterior of which correspond to the bifurcated bone of birds. The sternum, collar-bone, and first part of the scapula, form one piece. In the salamander, in which the same consolidation is observed, the scapular portion is most distinct and directed to the spine, while of the clavicular portion the part connected to the sternum stretches below the chest, but, without uniting with that of the opposite side, the right glides over the left,—an arrangement which facilitates the dilatation of the chest during inspiration.

A nearer approach still to the bifurcated bone than is seen in the Ranine may be recognised in the Cheloniad family. In these animals three bones are united to form the humeral cavity. The first is a flat, trilateral bone, situate below the abdominal and thoracic viscera, close to the abdominal shell, and which, notwithstanding its situation, is evidently the scapula. The second is a bone about the same length, flat, and like the feather of an ear at one extremity, which is free, round in the middle, and flattened in the opposite direction at the other end, which is firmly united at a right angle to a long slender cylindrical bone. At the angle of union of these two bones is part of the glenoid cavity, which is complete in the small end of the scapula. The first of the two bones is the collar-bone proper; the second is the lateral branch of the bone, which forms the bifurcated, and which is occasionally united with its fellow. (Plate XXXIV. fig. 5.) The abdominal shell we have already stated to represent the sternum or breast-bone.

The humerus in the Saurial and Cheloniad family is arched and incurvated in a serpentine direction. It is articulated with a radius and ulna, which are succeeded by three rows of carpal bones, one row of four metacarpal bones and digital phalanges, varying in number in different genera. In the skeleton of a fossil animal belonging to the Saurial tribe, originally delineated by Collini, and afterwards by Cuvier, and named by him the Pterodactylus or Wingtoe (Pterodactylus, Ossemens Fossiles, tome v.), the metacarpal bone and phalanges of the index are prolonged to about twenty times the ordinary length, for the purpose, apparently, of giving attachment to the membranous web by which the animal occasionally elevated itself into the atmosphere. This animal, which, like the dragon (dracon volans) of modern times, must have combined the contradictory characters of a flying reptile, may be regarded as forming the link between the Reptiles and Birds, as the Ichthyosaurus does between Reptiles and Fishes.

In the pelvis of the Cheloniad family it is remarkable that the pubal and iliac bones appear to change places. Thus the ilium on each side is a narrow bone proceeding backwards to the sacral part of the spine, which is received between its posterior aperture; while the pubis appears in the shape of a broad, trilateral, flat bone, uniting before with its fellow on the mesial plane, behind with the ilium, and below with a flat, thin, quadrilateral bone, corresponding to the ischium, with which it forms the oval aperture. The inner of these three bones presents, as usual, the cotyloid cavity. It is further to be observed, that the two iliac bones, and consequently the whole pelvis, are movable on the vertebral column. (Plate XXXIV. fig. 5.)

In the Saurial Reptiles the pelvic bones are arranged Pelvic and shaped nearly as in the Cheloniad. In the Ranine tribe the iliac bones are much elongated, and the pubal and ischial are consolidated into one piece, the symphysis of which forms a rounded crest.

The femur is short, thick, and incurvated sinuously, with the convexity before towards the tibial end, and the concavity towards the pelvic. Trochanters, though present in the Cheloniad, are wanting in the Saurial and Ranine Reptiles. In the leg we find both tibia and fibula distinct, and of nearly equal size, in the Cheloniad and Saurial family, but conjoined in the Ranine family. The tarsus consists of five bones, and sustains four or five metatarsal ones, on which are supported three rows of phalanges. The metatarsal bones, which vary in length, are longest in the crocodile and others of the Lacertine tribe. In the Ranine, again, the astragalus and calcaneum are the bones of greatest proportional length.

The anatomical characters now enumerated are proper to the skeletons of Reptiles at present existing on the surface of the earth or in its waters; and in these we find a gradual transition from the Saurial and Cheloniad, by means of the Serpentine, to the finny inhabitants of the ocean. Even the Batrachoid Reptiles, in the early period of their existence while tadpoles, we shall have occasion to see, approach to the Fishes; and in one singular genus, if not two, the Proteus anguinus and Siren Lacertina, the characters of the Reptile are combined with those of the Fish, in having at once lungs or internal respiratory cells, and gills or external ciliated branchiae. The transition thus indicated is still more strongly demonstrated in the osteological characters of two Genera of animals now extinct, so far as is yet known,—the Ichthyosaurus and the Plesiosaurus. From the specimens of the *Ichthyosaurus* hitherto discovered, it appears that the number of vertebrae varies from 80 to 90 or more; in one entire specimen they amounted to 104 (Conybeare and De la Beche); that they are flattened, with the transverse diameter greater than the longitudinal, and the two articulating surfaces of the bodies cayloid or cup-shaped as in Fishes. Though the annular part is distinct from the body, it is united to its sides. The spinous processes, which are long and prominent, form a continuous ridge above the spine, and are connected to each other by a process from the front of the one spine, which is inserted into a pit in the back of the other. Instead of proper transverse process, a certain number of the vertebrae are provided with two tubercles on each side of the body, of which the superior, convex, is articulated to the tubercle of the rib, while the other, which is concave, receives the head. In the inferior part of the vertebral column, these two tubercles, after approximating, are eventually identified into one.

The ribs, which are numerous, and extend from the occiput to the pelvis, are slender and trilateral in shape, bifurcated above, and attached to the vertebrae by a head and tubercle. In the perfect specimen of Mr de la Beche they amount to 31, and of these 17 appear to be cervical or anterior false ribs, with single tubercles; thus affording another mark of resemblance to the Saurial family in osteological characters.

The bones of the head, distinguished by the extraordinary size of the orbit, are similar to those of the Saurial Reptiles. The sternum, collar-bone, and scapula, though also similar to those of this family, bear a much closer resemblance to the figure of these parts in the Echidna and Ornithorhyncus. The humerus is short, thick, and sinuated; the bones of the fore arm flat, and probably constituting part of the fore or thoracic fin. The Carpus consists of three rows, the first containing three bones, the other two, four each. These are followed by five or six rows of flattened, irregularly cuboidal bones, gradually diminishing in size and number to the tips, and which represent at once the metacarpus and phalanges of the fore paw, used apparently chiefly as a fin or paddle. The pelvic extremities appear to have been less strong and perfectly constructed than the thoracic. The femur is smaller and shorter than the humerus; the tibia and fibula are flattened like the ulna and radius; the tarsus consists of two rows only, the first containing three, and the second five bones; and this in like manner terminates in five ranges of flattened bones, gradually diminishing in size, and which represent the metatarsus and metatarsal phalanges of the hind paw or paddle.

From the specimens hitherto discovered of the *Plesiosaurus*, it appears that the total number of vertebrae amounts to 90, of which 35 appear to be cervical, while the other 55 are dorsal and caudal, the regions of which are proportionally short. The head of this animal also is small and compressed, nor has it the large orbit of the *Ichthyosaurus*. Each rib consists of a vertebral and sternal portion, united at an obtuse angle, the former articulated by a single head to the transverse process, and the latter connected with its fellow by a transverse slip, so that the lower or abdominal ribs appear to have surrounded the abdomen with a complete cineture. The anterior part of the chest is occupied by two trilateral bones uniting in the middle, which, from their connection with the scapula, are believed to be the coracoid bones; and above these is a transverse piece, with a middle notch and lateral sinuated elevations, which is regarded as the sternum; while the scapula extends on each side like a buttress between the two. It is not improbable, nevertheless, that the middle portions named coracoid bones are the sternum, and the transverse bone the clavicles; and it is worthy of remark, that not only this bone, but the middle piece, closely resembles in figure and disposition those of the Echidna and Ornithorhyncus. The pelvis consists of three bones, a vertebral or superior, corresponding to the ilium, narrow and slightly incurvated; an anterior, ascending forwards, and broad, separating the pubis; and a posterior, short, forming the ischium. The humerus and femur are longer than in the *Ichthyosaurus*. There is a very short radius and ulna, and tibia and fibula, articulated with five carpal and tarsal bones; and the rest of both paddles consists of successive rows of flattened but long bones, contracted in the middle, and expanded at the extremities, representing the metacarpal and metatarsal digital phalanges. (Home, Phil. Trans. 1816, 1818, 1819, 1820; De la Beche and Conybeare, Geological Transactions, vol. v. p. 559; and Cuvier, Ossemens Fossiles, vol. v. part ii.)

**SECT. IV.—OSTEOLOGY OF THE FISHES.**

The Serpentine or Ophiad Reptiles present in their osteological characters an approximate transition to those of Fishes. While in the former order the skeleton is reduced to the spinal column, ribs, and head, in the latter class the spine and head only are left; and in some tribes the transition is still more distinctly marked by the presence of ribs.

The vertebra of a fish is distinguished from that of any other animal by the shape of its body. The cephalic and caudal, or anterior and posterior surfaces, are hollow cup-like cones, so that the union of each two vertebrae forms a double conical cavity, united by the base, containing a substance composed of concentric fibro-cartilaginous layers, with intermediate albuminous or gelatinous matter. By this cartilage the vertebral bodies are united; and on this the motions of the spine are effected. This motion, however, is chiefly lateral; for the spinous processes are so long, and the articulation so complex, that antero-posterior inflection or extension is nearly impracticable.

In the cartilaginous fishes, for instance the shark, sturgeon, and lamprey, the vertebral bodies form simple tubes, which, from the extreme elasticity of the constituent cartilage, propel the contained fluid to a considerable distance. Thus Sir E. Home saw the fluid projected to the height of four feet from the intervertebral cavities of the shark. (Phil. Trans. 1809.) In this order, also, the spine is infinitely more flexible, and its resilient power, when bent by the muscles, is almost incredible. On each side, also, the vertebrae are excavated, to form a canal for lodging the large blood-vessels.

The vertebrae of fishes are numerous, and not easily distinguished into classes. They may, however, be distinguished into two, according as the spinous process is above only, or above and below at once. Those with the dorsal spine only are denominated dorsal or abdominal vertebrae, and have commonly at the sides transverse processes for the attachment of the ribs. Those with the dorsal and ventral spines are distinguished as the caudal vertebrae. The last caudal vertebra is generally trilateral, flattened in the vertical direction; and its tip is marked with articular pits, which indicate the attachment of the small elongated bones which sustain the caudal fins.

The number of vertebrae varies. In the uranoscopus or star-gazer there are only 25, in the balista 17, and in the four-spined trunk-fish (ostacion) only 13; while in the sturgeon the number is 84, in the eel 115, and in the shark 207.

Though Fishes have no chest, and require none, since their respiratory organs are gills, all of them are not void of ribs. The ray, shark, symnathus, tetraodon, diodon, cy- Comparative Anatomy.

Comparative anatomy shows that fish have indeed no vestige of rib. But in the sturgeon, balista, etc., uranoscopus, pleuronectes, sea-wolf, and dory, they are in the shape of short rudimentary processes; in the trigla and loricaria their sides are horizontal; in the perch, carp, pike, and chetodon, they encompass nearly the whole upper region of the abdominal cavity; and lastly, in the silver-fish (zeus roemer), the herring, rhomboidal salmon, etc., they are united to a sternum. In the little animal named sea-horse (syngnathus hippocampus), several series of osseous tubercles of the skin, surrounding the body like belts, are supposed to represent false ribs. The sternum is limited to a small number of fishes. Besides those already mentioned, in the dory there is a series of minute flat bones disseminated along the lower edge of the belly, which is supposed to represent a rudimental sternum.

In size and number the ribs vary, though in the silurus, carp, and chetodon they are of largest proportional size; in the herring they are as fine as hairs.

The head. Cranium.

The head in the finny tribes is more an object of zoological than anatomical description. The chief points to be remarked are, that the cranium forms but a small part of the head; that the orbits are separated by a septum, sometimes membranous, occasionally, as in the wolf-fish, bony; and that there is on each side a large movable bone, corresponding to the quadrilateral of birds, not square, however, but oblong, which supports not only the lower jaw and palatine arches, but the gill-cover. In the cartilaginous fishes the sutures are early obliterated, and the cranium consists of an inseparable mass of cartilage. In the bony fishes the cranium is separable into numerous pieces, and in the perch they amount to 80. In the cranium of fishes the anatomist recognises more distinctly than in the superior orders the formation according to the vertebral type. Small in proportion to the whole head, the cranium appears like a direct continuation of the vertebral column. In the osseous division of the class especially, the cranium may be distinguished into the occipital or posterior vertebra, the spheno-parietal or middle, and the frontal or facial vertebra. The cavity thus formed is very small; yet small as it is, it is not exactly filled by the brain, between which and the bones there is interposed a pellicular fluid, contained in fine cellular tissue. The cranium of the osseous fishes also is widest between the ears, because the organ of hearing is contained within its cavity with the brain. In the cartilaginous it is quite different.

Though fishes are destitute of extremities similar to those possessed by the other three classes of the Vertebrata, they are not, however, without locomotive members. The thoracic extremities are represented by the pectoral fins, and the pelvic by the ventral. In short, it may be said that the bones of the thoracic and abdominal extremities are converted into osseous rays in the finny tribes.

In the Ray genus, in which the wing-like disposition of the pectoral fins gives the body a rhomboidal shape, they consist of numerous radiating cartilaginous lines, all attached to a cartilage parallel to the spine, divisible into two or three others, and articulated above to another adherent to the spine. Below there is a strong transverse bar common to the cartilages of both fins, and separating at once the sternum and clavicle. This transverse bar is also seen in the shark tribe; but their pectoral fins, which are much smaller, are not articulated with the spine.

In the osseous fishes, and in many others usually referred to the cartilaginous division, e.g. the balista, the pectoral fins are fixed to an osseous belt, which surrounds the body behind the gills, and which supports the posterior margin of their aperture. This belt consists of a single bone on each side, articulated to the posterior-superior angle of the cranium, and uniting below the breast with that of the opposite side. This bone, which may be regarded as a scapula, varies in shape and the angle which it forms with its fellow in different species. In fishes flattened vertically, the angle of union is acute; in those which are depressed, the angle is so obtuse as to form nearly a straight line. In many fishes, especially those of the order Thoracici, e.g. pleuronectes, cottus, zeus, chetodon, perch, etc., in the small unicorn (balista), and others, the superior part forms a large spine, which descends immediately behind the fin, and to which the adductor muscles are attached. This spine, which is movable, has been improperly named a clavicle.

The rays by which the membrane is supported are not directly articulated to this belt, but are connected by a row of minute flat bones, which may be compared to the corpus in the other three classes. When the first ray of the pectoral fin, however, is thorny, as in the harness-fish (loricaria), and some species of silurus, it is articulated directly with an osseous belt; and it is remarkable that some fishes, as the silurus and stickle-back, have the power of retaining this spinous ray erected against the body as a means of defence. This is effected by a cylindrical tubercle, on which the spinous ray is articulated by a hollow, bounded before and behind by an elevated process. When the spine is erected, the anterior process, entering a hole in the cylindrical tubercle, is locked in it by the spine revolving slightly on its axis, so that it cannot be indented unless by the spine revolving in the opposite direction.

The pectoral fins are so long that they answer the purpose of wings in several species of trigla, the trigla hipectoralis, the flying gurnard (trigla volitans), the springing gurnard (trigla evolans), in the scorpaena volitans, the tropical flying fish (exocoetus volitans), and some others. Their situation also is liable to vary. In the exocoetus they are near the gills, but in the bleennius and others they are remote. Lastly, they are totally wanting in a small number only, as the lamprey (petromyzon), the bag-fish (myxine, Lin.; gastroloranchus), the muraena, the cel genus, the sphyraenanchus, etc.

The abdominal or ventral fins, which correspond to the Abdominal pelvic extremities of the other classes, are so denominated or ventral because in the majority of fishes they are situate below the belly, and nearer the anal outlet than the pectoral. By this circumstance a numerous order are distinguished by the name of Abdominal Fishes (Abdominales).

In a small number of fishes, comprehending the gadus, bleennius, hirtus, callionymus, trachinus, and uranoscopus, the ventral fins are placed under the throat, below the aperture of the gills, and before the pectoral fins. This order is therefore distinguished by the name of Jugulares.

In the most numerous order of all, the ventral fins are situate behind and below the pectoral fins. These have therefore been denominated Thoracic Fishes (Thoracici).

The ventral fins consist of two parts—one formed of rays covered by a double membrane, apparent externally, and constituting the proper ventral fin; the other internal, representing the coxal bones of the pelvis, always supporting the pinnal rays, and often articulated with the bones of the trunk. It is never articulated, however, with the spine, nor does it form an osseous belt round the abdomen. The bones of which it consists are generally flattened, varying in shape, and in mutual contact by the internal margin. In the shark and ray genera only is there a single transverse bone, nearly cylindrical, to the extre- Comparative Anatomy.

The direction of the pelvic plane to the walls of the abdomen varies according to the shape of the body of the fish. In the flat fishes they are directed obliquely, and their inner margin forms the keel of the belly. In fishes with a broad or cylindrical belly they form a plane more or less horizontal.

In the Jugular and Thoracic Fishes, the pelvic bones are always articulated with the base of the belt which sustains the pectoral fins; and they vary much in shape and situation.

In the trachinus, uranoscopus, cottus, sciama, chetodon, and perch, these two bones are united by their inner margin. In the cuckoo-gurnard, in which they are united by the posterior tip only of their internal margin, they are broad, flat, and oval. In the sole and flounder genus (pleuronectes), in which the fins are attached to their anterior tip, they are united in a quadrangular pyramid, the apex of which is directed backwards and upwards, and the base forwards. In some of the stickle-backs these bones are altogether separate, and being long, receive in their middle a movable spine, which supplies the place of the ventral fin. In the dory (zeus faber, L.) they are flat and triangular, in mutual contact by their whole surface. In the silver-fish (zeus eomer) they are small and cylindrical.

In the whole of the Abdominal order, on the contrary, the pelvic bones are equally unconnected with the bones of the shoulder and with the osseous belt of the pectoral fins, and are confined to the middle-inferior part of the belly, not far from the anus. In general these two bones are separate from each other, and are retained in their situation by ligaments. In the carp, in which they are elongated, they touch only by their posterior third. In the herring, in which they are small and approximated, they are continuous with the minute bones of the sternum. In the pike they are broad and trilateral, approximated by their anterior tips, separate behind where the fin is attached. In the silurus, in which they are united, they form a round and often spinous shield before, while the fins are attached to the exterior-posterior margin. Lastly, in the cuirassier or harness-fish (loricaria), the pelvic bones are united in one piece, the posterior notch of which forms the anal aperture, while the fins are attached to its external margin.

The proper fin consists of a certain number of osseous rays, simple or bifid, supported by one or two rows of minute bones placed between them and the pelvic bones. On these small bones the constituent rays move, diverging or converging like the rods of a fan, while the whole fin may be inflected or extended by the minute bones moving on the pelvic, so as to adduct or abduct the fin.

In the cartilaginous fishes the structure is different. To the tip of each pelvic bone are articulated two principal cartilages, one external, forming a kind of toe with seven or eight joints; the other internal, supporting all the other rays of the fin, which often exceed thirty in number.

If we suppose these bones, like the minute ones of the pectoral fin, to represent the tarsus of the other three classes, it must follow that, in the locomotive extremities, the humerus, with the ulna and radius, and the femur, with the tibia and fibula, are obliterated. It is not unimportant to observe, that the general structure of the Vertebrata tends through various transitions to this termination. In the Amphibia the long bones of the extremities are shortened by removing the diaphysis, and leaving their articulating ends only. In the Cetacea the pelvic extremities are removed altogether. In the Chelomiad and Saurial Reptiles the same long bones of the extremities are much abridged; and in the Ichthyoid Reptiles, now extinct, but sharing by their structure a form of animal existence partaking of the reptile and fish at once, and perhaps intermediate between the two, this abbreviation is carried perhaps to its greatest possible degree, in leaving the articular ends only of the four locomotive extremities. Lastly, this reduction is merely preparatory to that exhibited in the whole class of Fishes, in which the three longitudinal bones so conspicuous in the higher classes of animals are completely obliterated, and those representing the hand or forepaw and foot are articulated directly to the shoulder and pelvic bones.

Besides the bones already mentioned as constituting the skeleton, there are observed in the osseous fishes minute bones, generally fork-like in shape, disseminated through all the muscular parts of the body. The purpose of these bones, which, as being totally insulated from the other parts of the skeleton, are denominated ossicula musculorum, is chiefly to afford points of support; and they are probably to be regarded as rudimental representatives of osseous parts, more completely developed in the higher animals.

It is further a curious circumstance, that the skeleton, which is so symmetrical in all the other classes and orders, of the finny tribes. In the Sole genus (Pleuronectes) this deviation is very conspicuous. Both eyes are placed on the same side of the mesial plane; and the side on which the eyes are placed is broader than the opposite one. The former is bounded by a convex margin, the latter by a concave one. The orbit towards the former is large, the other small and imperfect. Conversely, it is to be observed, that in the latter the maxillary and intermaxillary bones are larger than in the former. The sides of the inferior jaw are less discordant; and though in the Sole and Plaice those of the eyeless side are more straight and elongated than those of the other, in the Turbot (Pleuronectes maximus) they are nearly symmetrical.

CHAP. II.—COMPARATIVE MYOLOGY.

Though this is the proper place to consider the peculiarities of the muscular system of animals, the limits assigned to this sketch will not allow us to enter into details. We shall merely, therefore, take a cursory view of those points in which the myology of the lower animals differs from that of the human subject.

In general, in the lower animals, especially the Mammalia, Birds, and Reptiles, the muscles correspond in situation to those of the human subject; and whatever modifications they undergo consist in changes of figure, and in some few instances in changes in attachment. The former kind of changes may be in all cases pretty accurately estimated by the osteological characters of the class, order, or genus; for when the position, shape, or direction of a bone is altered, in the same proportion nearly are the attached muscles altered in their attributes.

Though in the lower animals, however, the zootomist traces muscles in general quite analogous to those of the human subject, in several instances this analogy ceases to be observed. In general the muscles of the lower animals are less numerous than those of the human subject; and this deficiency in number, though not much observed in the Quadrumania, is very remarkable in all the inferior orders of the Mammalia, and still more in the Birds and Reptiles. In general, also, these variations are most conspicuous in the locomotive extremities. Thus the small pectoral muscle, which is present in the Quadrumania, is wanting in the Carnivora and the whole of the Ungulated Animals and the Reptiles. The short supinator is present in the Canine and Feline genera, but the long is wanting; and both are absent in the Chiroptera, Rodentia, Pachydermata, Ruminantia, and... Solidungula, and in the whole class of Birds. Both pronators (teres and quadratus) are present in the Quadrupedans and Carnivora, but wanting in the Chiroptera, Ruminants, and Solidungula. The Rabbit, and perhaps the Rodentia generally, have the pronator teres; but as the radius is not very movable, its influence is trifling.

Myological peculiarities of the mole.

In the mole the rhomboideus is inserted into the cervical ligament, which is ossified; and it therefore elevates the head and neck on the scapula with singular force. This is effected still more remarkably by the occipital part of the rhomboideus, the fibres of which being parallel to the spine, pass below the proper rhomboideus to be attached to the transverse ligament and the middle of the cranium. The strong, thick, quadrangular collar-bone has two muscles, a supraclavarius and a subclavius. The large pectoral is very thick, and nearly as large as in birds.

The common extensor of the fingers or fore toes is the only muscle which is common to man and all the quadrupeds. Of the proper extensors the horse has two on the side of the common extensor, but acting as an extensor of the fore pastern; another between the common extensor and the extensor of the pastern, and which seems merely an appendage to the former. The proper extensor of the index is wanting in the Rodentia, Ruminants, and Solidungula; and while the two latter orders are destitute of the long and short extensors of the thumb, and the feline, canine, ursine, and leporine genera have the former, they are destitute of the latter. Lastly, the lower animals are wholly destitute of the short muscles of the hand, which in man produce flexion, abduction, adduction, and opposition. In the Chiroptera only is there one extensor, and flexors of the fore toes.

Among the muscles of the pelvic extremities the gluteus maximus, or large muscle of the buttock in man, diminishes much in the Quadrupedans; and in the other orders is reduced to a very small size. The buttock in the Mammalia generally consists chiefly of the gluteus medius and minimus; and while the gluteus maximus is in the horse in a great part aponeurotic, the g. medius is so large as to produce those forcible and sudden extensions of the hind leg which constitute the kick.

In the leg the sartorius of the horse, the animal in which the muscles have been most studied, is large, and is distinguished by the name of the long adductor, in opposition to the gracilis, which constitutes the short adductor. The muscle representing the biceps of man is in all quadrupeds a uniceps, and the single head is attached to the ischium only. In the horse and dog it has been denominated the vastus longus.

The gastrocnemius externus et internus (gemellus), which constitute the calf of the human subject, diminish considerably in the lower animals; and the soleus, which is placed below them, also becomes small, and is particularly slender in the Ruminants and Solidungula.

The following muscles are wanting in the whole class of Birds. The diaphragm, the recti abdominis, and the pyramidalis; the muscles of the dorsal part of the spine, the splenius, the trapezius externus, or third head of the triceps; the supinator of the forearm or wing, as already mentioned, all those corresponding to the short muscles of the hand and fingers; the quadratus lumborum, the psoas parvus, the psoas magnus, iliacus internus, obturator externus, and the extensor longus pollicis pedis.

Two muscles, which occupy the situation of the pronators, act as flexors, showing the connection between the actions of inflection and pronation, and the occasional substitution of the latter for the former.

In this class, also, the gluteus maximus is of a pyramidal shape, while the true pyriformis is wanting. The gluteus minimus, which is attached to the anterior edge of the iliac bones, is the iliacus. In place of the pectineus there is a slender muscle, which extends to the knee, over which its tendon passes, and gliding behind the leg, its tendon is bifurcated, one slip going back to be inserted into the posterior part of the metatarsus, the other to be united to the perforated flexor of the first and last toe. This muscle, which is named the accessory femoral flexor, is the one by which birds are enabled to clasp a perch during sleep.

In Birds the great pectoral is a remarkable muscle in point of size. It consists indeed of three muscles, used in large pectoral, the middle, and the small, which occupy the sides of the vertical crest of the sternum, and constitute what is named the breast of the animal; and which are chiefly employed in the energetic motion of the wings in flying. These muscles are sometimes so large that they weigh more than all the other muscles of the animal together. In birds which fly much they are dark coloured and firm; in those which fly little, as the domestic poultry, they are white coloured, and in general soft. The same distinction is observed in the muscles of the two extremities. In birds much on the wing these muscles are dark coloured and firm, while those of the legs are comparatively lighter and more tender; and, conversely, in birds little on the wing and mostly on the legs, as the domestic poultry and many of the Grollar, the waders, swimmers, &c., the muscles of the wings are light coloured and tender, while those of the legs are dark coloured, firm, and strong.

The flexor muscles of the leg and toes of Birds merit notice. They consist of muscles corresponding to the long flexors, which are divided into three masses. The first consists of five portions, three of which may be regarded as constituting a single common perforated flexor. It rises by two bellies, one attached to the external condyle of the femur, forming a perforated tendon, which receives one of those of the muscle corresponding to the peronaeus; the other to the posterior surface of the femur, forming the tendons of the index and small toe. This muscle is further connected by intermediate fibres with the accessory femoral flexor,—a muscle placed on the internal surface of the thigh, and sending its tendon over the knee; and as the tendons are inserted into the ungual phalanges, when the accessory femoral bends the thigh the flexors of the toes inflect them also, and retain them in the inflected position. By means of this arrangement birds are enabled to clasp a perch or other small body when roosting, without continued muscular effort, and thereby to sleep on the perch. This mode of explanation, which was originally given by Borelli, has been controverted by Vieq d'Azyr; but apparently not on good grounds.

Among the class of Reptiles, while the muscles of the Ophidian family are confined to those of the vertebrae and rudimental ribs, in the Cheloniad these are obliterated, and the muscles of the neck, head, and tail, and those of the locomotive extremities alone, are left. In the other two classes of reptiles the muscles are in general analogous to those of the Mammalia.

There are not many instances of muscles which, though unknown in man, are found in the lower animals. Of these the most remarkable are the cutaneous muscle (panniculus carnosus), and the suspensory of the eye. The former was absurdly maintained to exist in the human subject, especially by Nicolaus Massa; but it is manifest that the assertion was derived from the dissection of the lower animals only. It was not long after demonstrated by Charles Etienne, that no fleshy pannicle or cutaneous muscle exists, such as is found in the lower animals; and that the only cutaneous muscles in man are the *latissimus colli*, the *epicranthus* or scalp-muscle, and those which are attached to the face, and which by their motion give expression to the countenance. The cutaneous muscle even is not found in the Quadrupeds, nor does it exist in the pig. In various other animals, however, it is found in different degrees of distinctness. It is very well marked in the hedgehog and porcupine—by its means they have the power of erecting their spines, and rolling themselves up—and in the armadillo and the ant-eater tribe. In the mole, also, we have seen it pretty well marked.

It is an interesting fact, that Galen originally observed that the lower animals possess a seventh muscle of the eye, or one more than man. The suspensory or infundibular muscle (*musculus choanoideus*), as it has been named, from its shape, especially in the Ruminants and Solidungula, has the apex fixed to the margin of the optic hole, and its base inserted a little behind the four straight muscles. In the Zoophaga and Cetacea it consists of four parts, so that these orders appear to be provided with 8 straight muscles. In the rhinoceros it consists of two portions.

There is yet another part, the muscles of which can scarcely be said to exist in the human subject, but which attain a very great degree of development in the lower animals. The coccyx of the human subject is expanded in the lower animals into a highly flexible prolongation denominated the tail (*cauda*), variable in length, but always consisting of separate vertebrae, articulated and movable on each other. While the coccyx of the human subject possesses two muscles only, the *ischio-coccygeus* and *sacro-coccygeus*, which are so insignificant in size that they scarcely serve to move the part, the caudal vertebrae of the lower animals are moved by muscles greatly larger, more numerous, and more powerful.

The tail is to animals a much more useful and powerful organ than the coccyx to man. It is a member which peculiarly belongs to them; and though in ordinary circumstances pendulous, it is made to assume a variety of motions of which no other organ is susceptible, and to perform duties which would be otherwise impracticable. With many, as the long-tailed monkeys, the sloths, the ant-eater, and the squirrel tribes, it is indispensable as an organ of prehension. The majority of animals, as the Ruminants, Solidungula, &c., use it as a whip or lash to drive away insects. The lion, tiger, and others of the feline tribe, lash their sides with it when enraged. The Cetaceous swimmers employ it as a rudder and oar in the waters. The beaver uses it as a trowel, to enable him to construct his clay-built dwelling. An organ employed so variously must consist of a muscular apparatus rather complex.

The different motions of which the tail of the Mammalia is susceptible may be referred to three heads,—one by which it is extended or elevated, another by which it is inflicted or depressed, and a third by which it is made to beat the sides. The combination or succession of these motions gives rise to secondary ones more complex in character. It may be twisted on its axis, or turned in a spiral direction. These motions are effected by three classes of muscles.

1st, The muscles which raise the tail are situate above; they are *musculi sacro-coccygei superiores*. Commencing at the base of the articular processes of the 3rd last lumbar vertebrae, or those of the sacrum and the caudal vertebrae, by fleshy slips, they are connected to tendons, which are inserted into the base of the first of the caudal vertebrae, which are void of articular processes. The second tendon goes to the next following vertebra, and so on to the 13th, each contained in a ligamentous groove, which forms an investment. The muscles of both sides acting together, elevate or incurvate the tail upwards.

The *interspinalis* and *spinalis obliquus* or lumbo-sacro-coccygeal are the continuations of the *interspinales dorsi et lumborum*. The spinous processes, however, becoming indistinct, or being represented by two tubercles, the attachments vary.

2d, The muscles which depress or inflect the tail downwards take their origin within the pelvis, and are prolonged to various extents along the inferior surface of the tail. Of these there are four pairs, the *ileo-coccygeus* of Vicq d’Azry, the inferior *sacro-coccygeus*, the *inter-coccygeus* muscles, and the *pubo-coccygeus* of the same author. The insertions of these muscles vary in different genera, according to the number of vertebrae of which the tail consists. The pubo-coccygeus is wanting in the raccoon, but it is distinct in the dog and opossum. The effect of the ileo-coccygeal and it, is to depress the tail and apply it forcibly to the anus.

3d, There are only two muscles which carry the tail to the sides of the animal—the *ischio-coccygeus externus*, and the *intertransversalis* of Vicq d’Azry; the former proceeding from the pelvic surface of the *ischium* below and behind the *acetabulum*, to the transverse processes of the caudal vertebrae, the second extending in a continued band between all the transverse processes.

The tail, therefore, in the Mammalia, consists of a series of successively decreasing vertebrae, moved by eight pairs of muscles.

In Fishes it is not easy to trace any analogy between the muscles and those of the other classes. Though the spine, head and fins, have appropriate muscular bundles, the natural or fascial distinctions are less evident than in the other three classes. It is important, however, to remark, that while the muscles which move the spinal column are placed in these classes, partly before, and chiefly behind the vertebrae, those of Fishes are placed on each side. Hence the lateral motion of the spine, which is inconsiderable in Mammiferous animals, Birds, and Reptiles, becomes very conspicuous in the finny tribes, especially in the motion of swimming, while the antero-posterior inflection or extension is altogether insignificant.

It is almost superfluous to remark, that, in the greater part of the finny tribes, the muscles are white or pale coloured. In a few only, for instance the salmon, trout, gurnard (coregonus), herring (*clupea harengus*), carp (*cyprinus*), and some others, are the muscular fibres of a pale flesh red. The circumstances on which these differences depend are not known; but it is supposed that in the latter sorts the proportion of oleo-albuminous matter is more abundant than in the former. The proportion of albumen, however, in the muscles of fish, seems in general to be small. They abound in gelatine and isinglass; and in some of the cartilaginous fishes especially, the greater part of the muscles seem to consist chiefly of gelatine in various degrees of consistence. This is particularly the case with the lamprey, the hag-fish (*myxine glutinosa*), and even with the sturgeon. The sterlet especially (*acipenser Ruthenus*), a small species of sturgeon found in the rivers of Russia, both European and Asiatic, abounds in gelatine; and the presence of this principle enables the inhabitants to use it in the preparation of a species of soup, the sterlet, which is esteemed a great delicacy. In some of the genus *Pleuronectes* this principle is also very abundant. Thus the Plaice (*Pleuronectes Platessa*), sole (*P. Solea*), and especially the turbot (*P. Maximus*), contain a considerable proportion of gelatine. On the proportion of this principle depends the quality of fish used. Comp. Anat.

as an article of food in nourishing without exciting. All fishes which abound in gelatine uncombined with oleo-albuminous matter may be safely used as articles of food; while those in which the latter ingredients predominate are invariably eaten with the risk of disordering the stomach and producing indigestion.

CHAP. III.—COMPARATIVE ANTHOLOGY, OR THE COMPARATIVE ANATOMY OF THE ORGANS OF SENSATION.

SECT. I.—THE ORGAN OF SMELL.

The organ of smell consists of the nasal cavities, those of the ethmoidal and turbinated bones, and the frontal, sphenoidal, and superior maxillary sinuses, all of which communicate with the nasal. The whole of these parts are invested by fine periosteum, lined by mucous membrane. The ethmoid bone is the essential organ of smell; and the others appear simply to multiply the extent of the membrane.

The ethmoid bone consists of a perforated plate, with a middle vertical one attached at right angles to it, and lateral portions composed of thin bony plates convoluted with various degrees of complexity and minuteness in different orders and genera of animals. These convoluted plates form what are denominated the ethmoidal cells. They may be represented as numerous tortuous canals, proceeding from the perforated plate forwards and outwards, approximating mutually, and forming numerous communicating cavities. Such nearly is the structure of these plates in the Edentata, Ruminantia, Solidungula, Pachydermata, and Carnivora, the last of which have more complicated cells than the first. In the dog they are numerous and extensive. In the Rodentia, for instance the porcupine, they are few—not above 3 or 4 on each side.

In Birds the internal side of each nostril is occupied by three orders of plates; the inferior turbinate or spongy bone; the middle, consisting of one plate convoluted on itself two turns and a half; and the upper, shaped like a bell, adhering to the frontal and lacrimal bones. These form three tortuous passages, varying in size and tortuosity in different genera. Though generally cartilaginous, these turbinate bones are membranous in the cassowary and albatross, and bony in the calao and toucan.

In the nostrils of Reptiles there are convoluted prominent plates, which, however, are merely membranous productions, unsupported by any bone.

In the Fishes, in like manner, there are membranous folds, the disposition of which is tortuous. They are, however, more regularly arranged than in the other classes. In the cartilaginous fishes they consist of semilunar folds placed in parallel tracts on each side of a broad plate, which divides the one side of the nasal cavity from the other. In the sturgeon, however, they are arranged in diverging plates, which are subdivided into more minute ones, like the branches of a tree. In the osseous fishes generally they consist of radiating plates disposed round a prominent central tubercle.

In these three classes the olfactory nerve is distributed to the membrane much in the same manner. This nerve, however, does not proceed farther than the superior turbinate bones; and the middle and inferior appear to be supplied with filaments of the fifth pair, the naso-ophthalmic branch of which is distributed to the nose in all the vertebrated animals. In the Mammalia, further, the spheno-palatine ganglion sends several filaments to the posterior part of the narine membrane.

By most zoological authors the trunk of the elephant has been described as an organ of smell peculiar to that animal. We are satisfied, however, from observing the motions of this body in the living animal, that it is an organ, not of smell, but of prehension. Cuvier, after adopting the ordinary view, has relinquished it, and, on the ground of personal inspection, admits that the sense of smell in the elephant is confined, as in other animals, to that portion of the nasal cavities which is contained within the bones of the head. The trunk of the elephant, therefore, will with greater propriety be noticed under a subsequent head.

The nasal cavities of the Cetaceous animals are not so much organs of smell as channels of respiration, and must also be noticed afterwards. It is sufficient here to remark, that in these animals the part of the cranium corresponding to the ethmoid bone is penetrated by no aperture, or, in other words, is not an ethmoid bone. It has therefore been asserted that the Cetacea have no olfactory nerve, and no sense of smell. This, however, is by no means established. Blainville and Jacobsen have observed in the dolphin nerves which they regard as olfactive; and Treviranus delineates nerves of the same character. By Otto and Rudolph, on the contrary, who have had frequent opportunities of dissecting the dolphin and whale, the existence of these nerves is denied.

Though almost all the invertebrate animals give proofs of the existence of the sense of smell, in none of them do we find any organ in which this sensation appears with certainty to be exercised. That these animals possess the faculty of smell, is inferred from the fact, that insects recognise their food at a distance; that male butterflies scent the female even when inclosed in cages; and that the ordinary flesh-fly deposits her eggs on tainted meat, and occasionally on fetid plants, in the belief that they are the proper nidus, though in the latter case the larve perish for want of the necessary sustenance.

Since odorous particles are evidently applied to the olfactory membrane of all aeropnoic animals by the medium of the atmosphere, and since the organ of smell is therefore situate in connection with the wind-pipe, it was conjectured by Baster, that, in insects at least, the organ of smell is situate at the entrance of the trachea or air-tubes. This conjecture derives some probability from the fact, that the inner tracheal membrane in these animals is soft and moist, and that those in which it is expanded into convoluted lacunae and tortuous vesicles, for instance beetles, flies, and bees, are remarkable for the nicety of their sense of smell.

The antennæ, in which this sense has been placed by some anatomists, appear to be rather organs of touch than of smell.

In the Mollusca the whole cutaneous covering seems to combine the character of an organ of touch or tact, and of smell. Like an extensive pituitary membrane, it is soft, villous, moist, and liberally supplied with nerves. The Articulata and Zoophytes seem much in the same state. But on all these points information is rather conjectural than positive.

SECT. II.—THE EYES; THE ORGANS OF VISION.

All red-blooded animals, without exception, are provided with two movable eyes, consisting of the same essential parts as those of man, forming globular organs, and placed in the cranio-facial cavities named orbits. In none are there more or fewer; and the exceptions to the general rule, either in relation to the presence of these organs, or number, are only apparent. Among the Mammalia, Blind indeed, there are two instances of blindness,—in the zemni though not blind rat (Mus typhlus, Lin.; Spalax typhlus, Pall.), and eyeless the golden mole (Talpa Asiatica, Lin.; Chrysochloris, animals Laccp. and Cuvier). But in neither of these animals are the eyes absolutely wanting; they are merely very minute, and covered by a thin fold of hairy skin, in which there is said to be no aperture. Much in the same manner the *muraena coccinea*, and the bag-fish (*myxine, Lin., gastrophranchus eacus*), though provided with eyes, are deprived of the use of these organs by the opacity of the conjunctiva. In the *Anableps* (*Cotitis Anableps, Lin.*), the cornea and iris are biparted by transverse bands, so as to give the animal the appearance of having two pupils in each eye, though the crystalline lens, vitreous humour, and retina, are single. This animal affords the only example of this structure among the vertebrated animals; but a similar arrangement is observed in the Cephalopodous Mollusca and cuttle-fish family.

The general shape of the eye depends on the medium in which the animal lives. It is nearly spherical, or approaching the spherical shape, in man and the quadrupeds moving along the surface of the earth; that is, in the lowest and most dense region of the atmosphere. The cornea merely forms a slight convexity, in consequence of being the segment of a smaller sphere than the rest of the eyeball; yet in the porcupine, opossum, &c., this difference is inconsiderable. To show the degree of this convexity, it is merely requisite to compare the axis or antero-posterior diameter with the transverse diameter of the ball, as exhibited in the following table:

| Axis | Tr. Diam. | |------|-----------| | Man and ape | 137 | 136 | | Dog | 24 | 25 | | Horse | 24 | 25 | | Ox | 20 | 21 | | Whale | 6 | 11 | | Porpoise | 2 | 3 | | Owl | 13 | 12 | | Vulture | 13 | 16 |

According to the measurements of the younger Soemmering, the axis of the human eye, taken in a beautiful Tyrolese girl of 20, is to the transverse diameter as 100 to 95; that of the eye of the magot (*simia inus*) as 85 to 84; and that of the bat (*vespertilio auritus*) as 12 to 11. In the raccoon (*urus lotor*) and lynx (*felis lynx*) alone the axis is exactly equal to the diameter. In all the other vertebrated animals, it is, as in the measurements of Cuvier, less than the transverse diameter at the rate of from 9 to 33 or 45 per cent. In the horse it is as 186 to 212, in the seal as 130 to 142, in the Indian elephant as 135 to 180, and in the black whale (*balena mysticetus*) as 20 to 29. In the owl it is as 17 to 18, in the golden falcon as 14½ to 16, in the ostrich as 18 to 19½, and in the swan as 7 to 10. In the Reptiles and Fishes it is always less at the rate of from 3 to nearly 10 per cent. In the cuttle-fish, which may be taken as a general example of the invertebrated classes, it is much greater, the axis being to the diameter as 80 to 57. (D. W. Soemmering de Oculorum Hominis Animaliumque Sectione Horizontali Commentatio. Goetting, 1818, fol.)

In Fishes and the Cetacea which inhabit the sea, the anterior part of the eyeball is much more flattened, and in many fishes it resembles a hemisphere with the plane surface before and the convex behind. In the ray genus the superior part is also flat, so as to give the eye the appearance of the quadrant of a sphere, cut through two large circles perpendicular to each other. In some fishes, especially the burbot (*Gadus Lota*), the cornea is convex.

In Brains which occupy the elevated regions of the atmosphere, the deviation from the spherical shape is in the direction opposite to that of fishes. On the anterior part, which is sometimes flat, sometimes shaped like a truncated cone, is chased a short cylinder, closed by a very convex, and occasionally hemispherical cornea, always belonging to a much smaller sphere than the posterior convexity.

These differences in shape depend on the proportion between the density of the medium in which the animals live and that of the aqueous humour. In the higher regions of Comparative Anatomy, the atmosphere, in which the air is very much rarefied, the refracting power of the aqueous humour is much more considerable than at the surface, occupied by quadrupeds; and hence it is more abundant in the former than in the latter class. Its refracting power, however, would be almost extinguished in a watery medium, from which it could differ but little in density; and hence it is either trifling or absolutely wanting in the inhabitants of the deep. In the cuttle-fish family it is entirely wanting.

The crystalline lens in Fishes, which is nearly spherical, projects through the pupil, and leaves little room for the aqueous humour. The lens is also very convex in the Cetacea, the Amphibious Mammalia, the diving birds, as the cormorant, and the marine and aquatic Reptiles. Affecting the oblate spheroidal shape in the Mammalia, it becomes extremely so in man, and still more in Birds. Its consistence is greatest in animals in which it is most convex; and hence it is matter of common observation, that the crystalline of fishes is particularly firm. It also contains rather more albumen than the lens of the Mammalia. The crystalline lens occupies least proportional space of the eyeball in man, and most in fishes.

The comparative spaces occupied by each of the humours may be understood from the following table, in which the axis of the eye, or the space occupied by the whole three humours, is represented by unity.

| Axis | Tr. Diam. | |------|-----------| | Man | 137 | 136 | | Dog | 24 | 25 | | Horse | 24 | 25 | | Ox | 20 | 21 | | Whale | 6 | 11 | | Porpoise | 2 | 3 | | Owl | 13 | 12 | | Vulture | 13 | 16 |

On the proportion of the total volume occupied by each of the three transparent parts there are few accurate facts. It may be remarked, however, that the human eye among the Mammalia is that in which the vitreous humour is proportionally most abundant. It is estimated to be twenty times more copious than the aqueous. In the ox it is only ten times, and in the sheep nine times the quantity of the aqueous.

In the Mammalia generally, the sclerotic is comparatively elastic, soft, and yielding; but in all animals in which the eye deviates from the spherical shape, as the Cetacea, Fishes, and Birds, this membrane is strengthened by greater solidity and thickness of tissue, or supported by accessory parts of a hard unyielding structure.

In the eye of the whale these two parts, the hard and soft, are naturally distinguished in a very striking manner. The lateral parts of the sclerotic are nearly an inch thick, and very hard. The posterior part is about one and a half inch thick, and softer, because the spaces between the firm fibres are filled with oily substance. The posterior part presents for the optic nerve a canal one and a half inch long, the walls of which are formed chiefly by fibres in direct continuity with the dura mater—the only fact, it may be observed, which favours the statement of the ancient anatomists, that the sclerotic is derived from the dura mater. The sclerotic of the porpoise, though only two or three lines thick, has the same structure as that of the whale. In the seal it is thick before and thicker behind, but the middle zone is thin and flexible.

The sclerotic in Birds is thin, flexible, and elastic behind, with a bluish glistening aspect, and without distinct zones of fibres. The optic nerve enters, not by a hole, but an oblique canal. The anterior part consists of two plates, between which is enchased a zone of thin, hard, oblong, osseous Comparative Anatomy.

Imbricated over each other so as to give the anterior part of the eyelid a great degree of hardness, and a figure unsusceptible of change. Though these plates are nearly flat in most birds, and form an annular zone slightly convex, they are broad, arched, and concave internally in the owl genus, and form a bell-shaped tube, with the posterior aperture oval and the anterior round. This may be denominated the osseous ring (annulus ossium, zona ossae). In the ostrich it is narrow and flat.

Among the Reptiles, the Cheloniads possess an osseous zone, consisting of plates inclosed in the membrane without being continuous with its substance. They are also found at the lateral part of the sclerotic in the chameleon and some of the Saurial Reptiles, as the Crocodilus Sclerops and Lucius, the monitor, and the iguana (D. W. Soemmering). It is also an important character in the structure of the eye of the Ichthyosaurus, which indicates the connection of that animal with the Saurial tribe, that its sclerotic was provided with an osseous zone, consisting, as in these, of 13 separate pieces.

In Fishes the sclerotic is cartilaginous, homogeneous, semi-transparent, elastic, and, though thin, firm enough not to collapse. In the ray it is expanded into a tubercle, by which the eye is attached to a peduncle or stalk. The sclerotic of the sturgeon is so thick that it resembles a cartilaginous sphere, with the external part hollowed for the humours and membranes.

In the Cephalopodous Mollusca it forms behind a truncated cone, with the apex at the bottom of the orbit containing the gangliform swelling of the optic nerve, and several glandular parts, with the eye before.

The cornea has often been represented to be merely a continuation of the sclerotic; and though this is easily disproved by accurate dissection of the human eye and that of our ordinary domestic animals, its inaccuracy is much more manifestly demonstrated in the animal world at large. In the whale and rhinoceros the margins of the two membranes penetrate reciprocally. In man and the ox the corneal margin is enchased within the sharp imbricated edge of the sclerotic. In the tope-fish (equalus milandra, Lin.; galens, Cuv.) the cornea is observed distinctly passing within the sclerotic in the manner of imbrication. The cuttle-fish is destitute of cornea; and as there is no aqueous humour, the crystalline lens is covered by a fine thin membrane, extended beneath the conjunctiva.

In all animals provided with eyelids, the mucous membrane, after being folded behind the eyelids, is reflected forwards over the sclerotic and cornea, in the form of a thin, transparent membrane. In those void of eyelids, as most fishes are, the skin, passing into mucous membrane, is continued directly over the cornea, without forming any angular fold, and adheres strongly. This is very distinct in the cel, which may be flayed without leaving any trace at the site of the eyes, except a round, translucent spot. The same peculiarity is remarked in Serpents and in the cuttle-fish family. In the zemni, golden mole, blind cel, and hag-fish, it has been already stated that the cornea is covered by opaque mucous membrane.

The choroid coat exists in all animals yet examined. It is always very vascular. The inner layer, which has been distinguished by the name of tunica Ruyshiana, can scarcely be said to exist in man, small quadrupeds, and birds. In the large quadrupeds, however, especially the Cetaceous animals, it appears in the form of a distinct simple membrane like epidermis. The lateral and anterior parts of the membrane are always invested by a semifluid, viscid substance, of different shades of black or brown black (pigmentum nigrum); chocolate brown in the hare, rabbit, and pig; deep red brown in some birds; and purple red in the coloum. The absence of this dark-coloured pigment, which is not unfrequent, is observed in albinos, both human and animal, for instance white rabbits and white mice. The transparency of the Ruyshian membrane then shows the choroid of its natural red colour; and the pupil is red and contracted, and the eye intolerant of light.

In the Zoophaga, Ruminantia, Pachydermata, So. The lidungula, and Cetacea, the concave or inner surface of the Ruyshian membrane is diversified with colours of metallic lustre, more or less brilliant and something iridescent. In the ox it is of bright metallic green, changing to sky-blue; in the horse, buck, buffalo, and stag, it is a silvery blue passing to violet; in the sheep of a pale golden green, sometimes bluish; in the lion, cat, bear, and dolphin, of a pale gold yellow; and in the dog, wolf, and badger, of a pure white, surrounded by blue. This coloured part of the inner choroid surface, which occupies chiefly the side opposite to that on which the optic nerve enters, is named the tapetum. The use of it is by no means obvious. The explanation of Monro in reference to the tapetum of the ox, that it represents more distinctly to that animal the colour of his natural food, is not only frivolous, but inapplicable to the other genera.

The tapetum is wanting in all Birds and Fishes, excepting the ray, in which there is at the bottom of the eye a beautiful silvery-coloured space, produced by the transparency of the Ruyshian tunic, through which the tint of the choroid is seen.

In Fishes generally the choroid consists of two distinct separable membranes; the external, the proper choroid gland, white, silvery, or golden, very thin and not vascular; and the inner or Ruyshian, black, and consisting of a network of vessels. Between these two membranes is a body of a bright red colour, consisting of numerous tortuous vessels, convoluted and inclosed in pulpy filamentous tissue. Its general shape is that of a thin cylinder, encompassing the optic nerve like a ring, which, however, is incomplete at one side. This is the choroid gland,—a body about which there has been some difference of opinion, but which appears to be glandular rather than anything else. Its vascular structure is well seen in the globe-fish, percua labrax, and cod, in which they are very large, and form numerous anastomotic communications. They are generally covered by a white, opaque, viscid fluid.

The choroid gland is wanting in the Cartilaginous Fishes, the eye of which approaches more nearly to that of the Mammalia in this as in other circumstances. The choroid of the ray and shark genera is a threefold tissue of vessels, thick and consistent; the tunica Ruyshiana is very thin and semi-transparent; and between these is a layer of silvery matter with metallic lustre.

In the cuttle-fish genus, though between the sclerotic and choroid there are several glandular bodies, there are none between the choroid and Ruyshian tunic. The choroid is thick, soft, and vascular; the Ruyshian thin, firm, and dry; and though there is no tapetum, the whole interior surface of the eye is covered by deep purple, semifluid, viscid varnish.

Ciliary processes are found in all the Mammalia, Birds, Cillary several Reptiles, and even in the cuttle-fish among the processes Mollusca; but they are wanting in almost all fishes.

The indented border of these processes is more distinct, and is converted into a genuine fringe in the large animals, as the ox, horse, rhinoceros, and whale, in which the angle applied to the capsule is more acuminate than in other animals. In the Carnivora, particularly the lion, the base of the plates is shorter in proportion to the other sides than in the previously mentioned animals, so that the opposite angle is more prominent; nor is the The ciliary plates of Birds are mere serrated striae, without sufficient prominence to make them undulate in fluid. In the owl they are fine, closely set, and numerous; in the ostrich they are larger and more numerous; and in all, their extremities adhere firmly to the capsule of the lens.

In the tortoise the ciliary processes are so short that they are recognised only by the impression left on the vitreous humour; in the crocodile, however, they are distinct, and terminate each by an angle nearly right. They are indistinct in the toad, and imperceptible in the ordinary lizards and serpents.

The ciliary body and processes are large and distinct in the tope-fish; but if they are seen in any other of the cartilaginous fishes, they are wholly wanting in the osseous, in which the Ruysschian tunic is directly continuous with the weez.

The utility of these processes in retaining the lens in its position is nowhere so distinctly seen as in the eye of the cuttle-fish family, and especially the many-feet of the ancients (polypus octopoda). In these the ciliary processes form a large diaphragm or zone, in the aperture of which the crystalline lens is truly chased. They penetrate a deep annular furrow which surrounds the lens, dividing it into two unequal hemispheres, and cannot be detached without laceration.

The iris, of the same intimate structure as in man, is of a deep tawny or brown in the Mammalia, and marked with fewer coloured stripes than the human iris. In Birds it is of a uniform lustreless colour, varying according to the species, bright yellow, red, or clear blue. In the microscope it appears like a net-work formed by the intersection of numerous very minute fibres. The area is so fine that when the viscid varnish is removed it becomes transparent, and the iris appears of the same colour on both sides. In Fishes, conversely, the iris is so thin and transparent that the area is seen through it, of a golden or silvery brilliance, showing its direct connection with the choroid. Intermediate in metallic splendour is the iris of the Reptiles. The vessels, however, are greatly more conspicuous, especially in the crocodile.

The central aperture or pupil, though round in man, the Quadruped, many of the Carnivora, and Birds, is not of that shape when contracted in all animals. In the feline family it consists of two elliptical segments, which form angles above and below, and which approach mutually so as to form a slit nearly vertical. In the Ruminants it is oblong transversely, and forms at its greatest contraction an oblong or transverse slit. In the horse, in which it is also transverse, its upper margin is distinguished by a five-pointed festoon. In the whale it is oblong transversely, and in the dolphin it is heart-shaped. The pupil of the crocodile resembles that of the cat; in the frog and gecko it is rhomboidal; and round in the tortoise, chameleon, and common lizards. In the ray among Fishes the upper margin forms several radiating slips like the branches of the palm-tree, gold-coloured without, dark within. In the dilated state these slips are folded backwards between the upper margin of the pupil and the vitreous humour; but when the eye is pressed they are erected, and close the pupil like a blind.

The motion of the pupil is voluntary in the parroquet, and is indistinct in most of the Fishes.

The pupillary membrane is well known to exist in the fortuses of all the Mammalia; but it is not determined whether it is found in the chick of birds.

On the subject of the retina in the lower animals the most important point is the structure of the melanoplectic or pectiniform membrane (pecten, marsupium nigrum) of Birds. In this class the optic nerve forms not a round disk, as in the Mammalia, but a narrow white line, the margins and extremity of which are in continuity with the retina. Along this line is suspended a plicated or convoluted membrane, very fine and vascular in structure, like the choroid, from which, however, it is quite distinct, and entering a depression of the vitreous humour almost like a wedge. Its vessels, which proceed from a proper branch of the ophthalmic artery, are distributed in a minute arborescent form, among the folds of which the marsupium consists; and from these vessels the black viscid pigment with which its folds are covered appears to be secreted. The plicae or membranous folds vary in number. In the cassowary they are only 4; in the brown owl (S. aluco) 5; in the common owl, ostrich, Guiana macaw, and merganser, they are 7; in the flamingo 9; in the falcon and swan 11; in the vulture and goose 12; in the duck, large heron, woodcock, and coot, 13; in the stork and partridge 15; in the crane 17; in the pheasant 20; in the turkey 22; in the jackdaw 25; and in the thrush 28. According to the observations of the elder Soemmering, to whom we are indebted for these numbers, the number of folds, though variable in different species, is the same in the same. In most birds the folds are arranged in a pectiniform order. On the use of this organ different opinions have been entertained by Petit, Haller, and Home; but all of them are conjectural.

In the Reptiles and many Fishes, between the optic nerve and the retina is a small tubercle, from the margins of which the latter membrane appears to rise; and radiating fibres are perceived more distinctly than in most quadrupeds. In many other Fishes the connection of the retina with the optic nerves resembles that of Birds. Thus, in the salmon, trout, herring, mackerel, cod, dory, and moon-fish, the optic nerve, after passing through the Ruysschian tunic, appears to be parted into two long white processes, which, following the outline of this membrane parallel but not contiguous to each other, are connected with the retina by their opposite margins.

In all animals provided with ciliary processes the retina terminates at and is connected with the gray pulpy zone denominated ciliary ligament. In those without ciliary processes, as the Fishes, it terminates suddenly at the attached or large margin of the area.

In several of the reptiles the retina presents the yellow spot of Soemmering. The principal peculiarities of the humours have been already mentioned.

Of the appendages the most important are the lacrymal gland and nictitating membrane.

In the Ruminants the lacrymal gland consists of two or three bodies, each composed of granules, each provided with a separate short excretory duct. In the hare and rabbit, in which the gland is large, there appears to be only one excretory duct, which perforates the upper eyelid near its posterior angle.

A gland peculiar to certain species, and wanting in man, that of Harder, is situate at the external or nasal angle, and presents an aperture under the third or nictitating eyelid, from which issues a thick viscid fluid. It is found in the Ruminants, the Rodentia, the Pachydermata, and in the sloth genus.

The caruncle exists in the Ruminants as in man, and appears to consist of numerous aggregated follicles. It is wanting in the Rodentia.

In the Cetacea, as in most animals which live under water, there is neither gland nor lacrymal passages; and they are represented apparently by lacunae below the upper eyelid, which discharge a thick mucilaginous fluid.

Birds, though destitute of caruncle, have both lacry- Comparative Anatomy.

The third eyelid or nictitating membrane.

In warm-blooded animals generally, that is, in the Mammalia and Birds, the labyrinth or essential part of the organ consists of three semicircular canals, with a globular enlargement to each (ampulla), a cavity common to these canals named vestibule (vestibulum), and a conical tapering canal, divided into two compartments by a longitudinal septum. This may be named the bilocular cone (conus bilocularis). These parts consist of membranous substance inclosed in the bony walls of the pyramidal or auditory bone. In all the Mammalia the bilocular conical canal is convoluted in a spiral form, and hence is denominated, as in man, the cochlea—a name, however, which is applicable to it in this class only.

The organ of hearing in the Mammalia consists of the same parts nearly as in man. In some, indeed, for instance the guinea-pig (cavia), and porcupine, the cochlea makes three turns and a half; and, conversely, in the Cetacea only one and a half. In most of the Zoophaga, and in the hog, elephant, and horse, the cochlea is much larger in proportion than the semicircular canals; but in the hare it is small, and in the mole very small. In the Cetacea, while the cochlea is very large and fully developed, its spiral is on the same plane throughout; and the semicircular canals are so small, that their existence was long denied by Camper, till they were demonstrated by Cuvier in a fetal whale. In general the labyrinth of the Mammalia is greatly smaller in proportion to the head than in Birds.

This part, which is membranous, is inclosed in the solid compact substance of the temporal pyramid, so closely that its existence appears to be identified with the latter. Researches, however, on the labyrinth in the fetus of the Mammalia, and especially in those of whales, demonstrate the fact that it is in a completely membranous form, distinct from the bony inclosure; that in shape and constituent parts it exists previous to the bony inclosure; and that the latter is afterwards moulded round the different parts as they acquire their full development. It is also to be observed, that in the mole the semicircular canals are seen within the cranium without preparation, and the cochlea is merely inclosed in fine cellular tissue. In the bat family, also, both parts are seen without bony inclosure.

The tympanum forms a cylindrical or spheroidal cavity in Typhlops, most of the Mammalia. In most of the Digitata the mastoid process consists of a slight prominence of the tympanum only as it is identified with the latter; but in the cavia, guinea-pig, hog, the Ruminants, and Solidungula, it is represented by a long process of the occipital bone. In most of the Zoophaga and Rodentia the parietes of this protuberance, which are thin and hard, form by their separation a large cavity. In the hog only it is occupied by a firm cancellated structure.

All the Mammalia, except the ornithorhyncus, have the tympanal bones as in man; the hammer (malleus), anvil bones (incus), orbicular bone and stirrup (stapes). The lenticular bone, which is rarely found in the adult, is probably only an epiphysis of the anvil. They are articulated with each other so as to admit of motion, and are moved by the same muscles as in the human subject—the internus mallei, externus mallei, laxator tympani, and stapedius. In the ornithorhyncus, however, there are only two tympanal bones.

In all the Mammalia, except the Cetaceous, the ear External is provided with a bony external canal (meatus); and aperture, most of the Mammalia, except the Cetaceous, have a cartilaginous funnel-shaped opening (concha) attached to the outer margin of the bony meatus, and which serves to...

Collect the sonorous vibrations, and direct them to the meatus. The other exceptions are among the Insecti- vora, the mole, and some of the shrew genus; among the Rodentia, the zemi or blind rat, and some of the rat- mole genus; among the Edentata, the pangolin or scaly ant-eater; and among the Amphibia, the morse and sev- eral species of seal; and the ornithorhynchus paradoxus.

The tympanum of the Cetacea is peculiar. It con- sists of a bony plate, convoluted on itself like a buccinum, unless that the thick side, instead of containing a spiral cavity, is entirely solid. The opposite side is thin, with an irregular margin. The anterior extremity of the tym- panum is open, and there commences the Eustachian tube, which ascends along the pterygoid process, and, pe- netrating the maxillary bone, terminates at the upper part of the nose. This direction of the tube and position of its orifice is so much more necessary, because, since these animals have no external bony meatus, and the ear-hole scarcely admits a pin, the vibrations of the air reach their organ of hearing entirely by the Eustachian tube, and because the Eustachian tube also in these animals conveys odorous impressions to the part in which the sense of smell appears to reside. The aperture by which it communicates with the nose is provided with a mem- branous valve, which prevents the water from entering when the animal expels it by his nostrils.

In Birds, of the three semicircular canals the vertical is largest, and obliquely directed forwards and outwards; the second is horizontal and turned outwards; and the third, which, like the first, is vertical, crosses the second, and is turned in the direction opposite to that of the first. The vestibule is small and nearly spherical. The bilocu- lar cone, which is obtuse at the apex, is situate obliquely backwards and outwards below the inferior part of the cranium. The longitudinal septum consists of two nar- row cartilaginous plates connected by a thin membrane. The posterior canal is short, and, as in the Mammalia, is separated from the tympanal cavity by the membrane of the fenestra rotunda; while the anterior, which is larger, communicates directly with the vestibule. The whole of these parts are inclosed, as in the Mammalia, in the compact bone of the pyramid.

The posterior and inferior walls of the tympanal cavity are formed by part of the occipital bone; the lateral aper- ture is large, and the cavity superficial; and its anterior part is closed by the posterior superior cornu of the quad- rilateral bone and a membrane. The inner wall presents the two apertures—the oval or vestibular, and the round or cochlear. In this class, however, while the upper is round or triangular, the lower is distinctly elliptical,—a disposition the reverse of what is observed in man. The Eustachian tube or tympano-guttural canal is entirely os- seous. The tympanal cavity contains only one ossiculum, consisting of two branches; the first attached to the tym- panum, corresponding to the malleus; the second closing by an oval or triangular plate the vestibular aperture, and therefore corresponding to the stapes of the Mammalia. By Carus the incus is supposed to be represented by the quadrilateral bone.

The external meatus is short, and opened by a simple aperture, while the absence of external ear is compensat- ed by a ring or zone of fine elastic feathers with thin barbs, between which the air passes very easily. In the owl tribe it terminates in a large cavity, the margins of which are covered by a smooth valvular fold of skin.

The ear of the Reptiles is remarkable for the last ap- pearance of the bilocular cone, and the first of the sac- cular apparatus which is found in the Fishes. In the cro- codile and lizard this part appears, as in Birds, in the shape of a conical tube, divided by a cartilaginous partition into a double canal, one separated by the membrane of the round hole from the tympanal cavity, the other communicating with a membranous sac containing three very small friable stones, not harder than starch. There are also three semi- circular canals of considerable size, each forming a large circumference. In the frog and toad, while the three canals Lithopho- form almost a complete circle, the sac contains an amylaceous sac ceous friable stone; but the bilocular cone is no longer and amy- observed. In the salamander, also, in which the three canals form together a sort of equilateral triangle, the sac which is below contains a single amylaceous stone. The same arrangement is observed in the Cartilaginous Fishes, unless that the sac contains two amylaceous stones, nearly oval in shape, suspended in a gelatinous semifluid pulp. In the Osseous Fishes it is a little different. The three semicircular canals terminate in a membranous sac, which is divided by septa into compartments which contain one, two, or three small stones suspended in gelatinous fluid. These minute stones, however, instead of being soft, fri- able, and amylaceous, as in Reptiles and cartilaginous Fishes, are as hard as rock, and white as porcelain. These parts are situate on the sides of the cranial cavity, and are fixed to it by cellular tissue, vessels, and osseous or cartilaginous processes. This sac, in the fluid of which the extremities of the auditory nerve are distributed, is believed to correspond to the bilocular cone of the higher classes.

These membranous cavities are contained, in the bony fishes, in the general cavity of the cranium; and while only the middle of the canals is inclosed in the bone of the cranium, the extremities and the sac are quite free. The sturgeon, which belongs to the cartilaginous order, is the first in which the canals are entirely inclosed in the cra- nial cartilage; but even in this a membrane is interposed between the cranium and sac, which is free. In the ray and shark genera, again, these organs are entirely in- closed in the cartilage of the head.

The tympanal cavity, in like manner, is modified, and eventually disappears as we descend in the scale. Though present in the tortoise, crocodile, and lizard tribe, it is superficial and open; it becomes membranous behind in the Ranine tribe, and communicates directly with the back of the mouth; and in the Serpentine reptiles it entirely disappears, so that the handle of the osseous plate by which the oval aperture is closed is suspended in the soft parts with its free extremity below the skin, near the articulation of the lower jaw. In the lizard tribe, also, Cochlear the round or cochlear aperture is seen for the last time.aperture In the Chelonid, for instance, the Batrachoid, and the Serpentine, the aperture disappears, and the oval or ves- tibular aperture is left; and in the salamander both dispa-Vestibular pear, and there is no communication between the external aperture part of the cranium and the labyrinth. This arrangement disappears. is continued in the fishes.

In the molluscous animals the labyrinthine membrane is a simple sac, globular or ovoidal, containing pulpy matter, in which is suspended a small body, which is osseous in the sepia and amylaceous in the many-feet (polypus), in which the filaments of the auditory nerve are distributed.

Our limits do not allow us to enter into the detailed description of the organ in the other Invertebrate animals.

SECT. IV.—THE ORGAN OF TASTE.

Though the sense of taste is seated chiefly in the tongue in animals, yet that organ performs, in all the classes, so important a part as an instrument of prehension, that it cannot with much justice be distinguished by the former title only. In the present section, therefore, we must regard it as one of prehension as well as of taste. In the Mammalia and Birds the tongue is a muscular organ invested by mucous papillated membrane, supported by a proper bone, the hyoid, which serves as a point of support in its various motions. In the Ranine Reptiles it is also muscular, attached to the margin of the lower jaw. In the salamander, however, it is attached as far as the tip, and is movable on the sides only. In the crocodile it is attached so generally, both by tip and margins, that it was long asserted that the animal was tongueless. In the stellio and iguana it is as movable as in the Mammalia; and in the scinc and gecko to this property is added that of being bifid, or divided by a longitudinal notch into two pointed tips. In the ordinary lizard, tu-pinambis, monitor, &c., the tongue is remarkable for its great extensibility, and terminates in two long, flexible though semi-cartilaginous extremities. That of the chameleon is still more extensible, and forms, by a peculiar arrangement of vessels, a cup-like extremity. The tongue of the blind worm (anguis fragilis) and amphibrama is also bifid at the tip. The cartilaginous fishes are void of tongue, while in the bony division of the class this organ is represented by a hard protuberance, attached to the middle branchial bone.

In some of the Mammalia, however, the tongue is not exclusively muscular. In the singularly long, extensible, and tortuous tongue of the giraffe, Sir Everard Home describes a peculiar arrangement of vessels, which he represents as a substitute for muscular motion. Though Sir Everard does not appear to understand the exact nature of this arrangement of vessels, all the circumstances tend to show that it is that denominated erectile. These vessels, from the account given, are large, numerous, and communicate freely; and it would be impossible to discover the reason of such a vascular system, unless for some purpose of this description. (Phil. Trans. Comp. Anat.)

When the tongue is protruded it becomes perfectly black or bluish-black, evidently from the injection and detention of the blood in its elongated and anastomosing veins. By means of this mechanism the giraffe not only elongates the tongue to the distance of about twenty inches or two feet beyond the mouth, but twists it round the soft leafy twigs of the trees on which he feeds. It is not improbable that a similar vascular arrangement exists, though in less degree, in the tongue of the deer, and in the long projectile tongue of the animals of the ant-eater tribe, as the Tamanoir, Tamandua, &c.

The erectile arrangement is still more distinctly presented in the tongue of the chameleon. The researches of Mr Houston of Dublin show that the tongue of this animal consists of two parts,—a prehensile, which is anterior, and provided with a glandular apparatus for secreting the viscid fluid by which its tip is covered, and insects are entangled; and an erectile, which is posterior between the prehensile and the hyoid bone, in the form of a trellis-work of innumerable minute anastomosing blood-vessels, not very dissimilar to those of the cavernous body in animals generally, and inclosing a central tube connecting the prehensile portion to the hyoid bone. The effect of this arrangement is, that when the vascular network is injected with blood, the anterior part of the tongue is rapidly darted out at the insects on which the animal lives. The injection of these vessels, and the consequent projection of the tongue, is not independent altogether of the will of the animal; for the veins by which the blood is returned pass through a slit in the tendon of the internal cerato-maxillary muscles, which are always contracted in order to protrude the hyoid style, and thereby tend, by compressing the veins, to inject the erectile part, and project the tongue. (Trans. R. I. Acad. 1828, and Dublin Hospital Reports, vol. v. p. 487.) The same arrangement is in all probability found in several of the lizards, the tongues of which, like that of the chameleon, are darted out suddenly, and become of a dark-blue colour at the moment of projection.

In all the Mammalia the tongue is invested by a papillated muco-villous membrane, in which the papillae are of the same general characters as in man—granular, mushroom-like, or fungiform, tubercular or calycoid, and conical or acuminated. The only differences consist in the size and abundance of the fungiform papillae, in the number of the calycoid and the mode of their arrangement, and in the shape of the conical papillae and the mode of their termination. In the Ruminants especially, the conical papillae are numerous, long, slightly incurved, and each terminating in a horny but flexible style slightly incurved backwards. The tongue of the dolphin and porpoise, examined even by the microscope, presents no distinct conical papillae, but is covered by minute eminences, each penetrated by a small aperture.

In the tongue of the dog genus there is a ligamentous Worm of substance extended longitudinally from the hyoid bone to the tip of the member. This, which has been vulgarly absurdly distinguished by the name of worm of the tongue, and has been absurdly supposed to be the seat of hydrophobic rabies, is merely a central pillar of support for the muscular fibres to act with greater steadiness and effect, and which enables the animal to protrude and expand the tongue in lapping water or other fluids better than he could have otherwise done. A similar central ligament is found in the opossum.

The tongue of Birds is generally more or less horny, and almost cartilaginous. That of the woodpecker and wryneck is peculiar in consisting of two parts,—a basilar or posterior, loose and fleshy; and an anterior projectile, long, smooth, acuminated, and covered laterally with four or five stiff spines directed backwards, which make the organ a sort of barbed arrow. The soft, loose, or basilar part of the tongue contains the aperture of the glottis; and the surface is covered with minute spines pointed backwards, and each of which is placed in the centre of a fleshy papilla.

As a prehensile organ of very singular construction, Trunk of the trunk of the elephant deserves particular notice; and the it cannot be more conveniently introduced than under the present section, since it is used not only to convey food, but drink, into the mouth. The trunk may be described as a cylindrical tubular organ, consisting of integument, a sort of fibro-cartilage, muscles, fat, and a membrane of villous character internally. This tube contains two long canals continued from the nostrils, parallel to the axis of the trunk, and separated throughout by a partition of adipose substance about two fifths of an inch thick. From the extremity to the middle part of the intermaxillary bone, in which the tusks are fixed, these canals are nearer the anterior-superior than the posterior-inferior part of the tube, the latter wall being thickest; and their diameter is the same throughout. At this part they undergo a sudden incursion, approaching the anterior surface of the intermaxillary bone, and form a semicircular bend with the convexity turned forwards. Here also they are so narrow that, without a muscular effort on the part of the animal to dilate them, fluids could not ascend beyond this point; and hence this forms the only valvular contrivance, either to impede the progress of fluids upwards, or to propel them downwards, at the will of the animal.

Above this curvature each canal is dilated before the upper part of the intermaxillary bone, and again is contracted where it bends back to enter the bony nostril; and the curvature is protected before by the nasal cartilage, which is oval, convex in the male, and flat in the female. Both canals are lined by a dry, greenish-yellow coloured membrane, marked with superficial intersections (rugae), inclosing rhomboidal spaces, and some venous branches.

Though the muscular fasciculi of the trunk are numerous, they may be referred to two orders,—those forming the substance or inner part of the organ, and those by which it is invested. The former, which are transverse, and cut the axis in different directions, consist of numerous small muscular packets proceeding in various directions, some running from the inner membrane to the circumference of the tube, others directly from right to left, and others crossing the two former obliquely. All these little muscles are inclosed in cellular tissue, containing white homogeneous fat; and all of them terminate in slender tendons, some of which cross the layers of the longitudinal muscles in their course to the external covering, while others are attached to the internal membrane.

Cuvier calculates the number of these minute transverse muscles in the trunk of the elephant to be not fewer than 30,000 or 40,000. (Plate XXXVII. fig. 13.)

The longitudinal muscles, which are external, may be distinguished into anterior, posterior, and lateral bundles. The first extend from the anterior surface of the frontal bone, above the nasal bones and cartilages, in parallel bundles, connected by tendinous intersections downwards on the trunk. The posterior extend from the posterior surface and inferior margin of the intermaxillary bones, and form two layers which meet on the median line along the lower surface of the trunk. The lateral muscles form two pairs, one of which, descending between the anterior and posterior muscles to the middle of the trunk, may be regarded as a continuation of the orbicular muscle of the lips, or the representative of the nasalis labii superioris; while the other, which is attached to the anterior margin of the orbit, and is expanded over the root of the former, may be supposed to correspond to the levator of the upper lip.

The whole of these muscles are supplied by a very large branch of the infraorbital or second branch of the trigeminal nerve, which, entering on each side between the lateral and superior muscle, is distributed to the whole of the trunk.

With such a construction, it is not difficult to understand the numerous motions of the elephant's trunk. While the longitudinal muscles are employed either to shorten the tube, to bend it upwards or downwards or to the side, or by means of the tendinous intersections to give it peculiar inflections, it is manifest that the transverse ones, which act as antagonists to the longitudinal, may also either dilate or close the canals, or incurve or alter the direction of particular parts.

The foot of the Lacerta Gecko and the house-fly presents a prehensile apparatus of peculiar construction for walking along surfaces, in opposition to the action of gravity. In the former animal the plantar surface of each toe presents sixteen transverse slits, leading into an equal number of pouches, which by means of appropriate muscles are capable of forming an equal number of vacuæ, so that the atmospheric pressure is employed with muscular effort to support the animal in his unnatural position. A similar apparatus is found in the upper surface of the head of the sucking fish (echeneis remora); and something approaching to it, though less distinctly, in the foot of the walrus. (Home, Phil. Trans. 1816.)

CHAP. IV.—COMPARATIVE ANATOMY OF THE ORGANS OF VOICE.

Under this head our limits allow us to mention very few circumstances.

In the American long-tailed monkeys (sagajous) the cuneiform cartilages form, by means of adipose cellular tissue, before the upper extremity of the ventricle of the glottis, a large cushion like a spherical segment, which, touching that of the opposite side, causes the air to whistle through the canal in its course to the mouth, and occasions the flute-like voice of some of these animals, as the weeper (s. apella) and the capuchin (s. copacina). In the Voice of howler (s. seniculus), so remarkable for its morning and the howler evening yelling, though the larynx is similar in general appearance, characters to that of the common sagajous, in having the two rounded cushions before the ventricles, the hyoid bone is arched in the form of a spherical chamber, with a large quadrilateral aperture, and each ventricle opens into a membranous sac, lying between the epiglottis and the adjoining wing of the thyroid cartilage. The air, which passes between the vocal chords, is therefore partly impelled into this osseous and elastic cavity of the hyoid bone, and probably by its resonance in this situation gives the voice of these animals the deep-toned howl by which they are known in the American forests.

Among the Zoophaga, in the dog the cuneiform cartilages are large, the arytenoid small, the vocal chords well marked, and the ventricles deep. In the feline tribe the anterior ligaments, though destitute of cuneiform cartilages, are thick, and separated from the back of the epiglottis by a broad, deep furrow. The posterior ligaments, though neither free nor sharp-edged, are distinguished from the anterior by an appearance of greater firmness, more regular fibres, and by an intermediate furrow. The approximation of the anterior ligaments towards the glottis forms a sonorous vault, in which the air may be forcibly vibrated by the posterior. In the bear the cuneiform cartilages assume the shape of styles, and their posterior extremity forms a distinct eminence, not above, but without the arytenoid cartilages, while the ventricles are merely deep fissures.

The kangaroo has neither cuneiform cartilage, anterior ligament, nor ventricle; and it may even be said to be void of vocal chord, while the margins of the glottis are much separated in the middle. This arrangement appears to indicate that the animal is almost destitute of voice. In the opossum, in which there is merely a small inferior ligament susceptible of tension, voice is limited to a whistling sound.

In the Solidungula, in which the cuneiform cartilages are completely concealed by the mucous membrane, there is neither superior ligament nor proper ventricle; but an aperture in the lateral wall of the laryngeal membrane, above the vocal chord, leads into a large, oblong, sinuous cavity, situate between this membrane and the thyroid cartilage, and covered chiefly by the thyro-arytenoid muscles, by which it may be compressed; and above the anterior commissure of the vocal chords, or below the base of the epiglottis, is an aperture on the mesial plane, leading into a cavity below the vault formed by the anterior margin of the thyroid cartilage. This cavity, which may be named the infrathyroid, is superficial in the horse, of the ass, and its aperture is large; while in the ass, with a small, round aperture, the cavity is large, capacious, and globular in every direction, and allows the latter animal to make his voice re-echo in the singularly harsh sound denominated the bray. Conversely, though the lateral cavities are equally large in both animals, the apertures in those of the ass are small, round, and situate nearer the epiglottis than the vocal chord, while those of the horse are large, oblong, and situate immediately above the vocal chord on each side. On the latter peculiarity appears to depend the neigh of the horse.

In the Cetacea we recognise neither vocal chords nor glottis, that is to say, an aperture variable in size according to... According to the will of the animal; but the superior part of the trachea, which represents the larynx, forms a hollow pyramid or funnel, rising into the posterior part of the nostrils, in which only it opens, while on the sides is left a passage for the food. This pyramidal funnel is formed by an elongated triangular cartilage, corresponding to the epiglottis, attached by membrane to the arytenoid cartilages, which also take the shape of scalene triangles, with the small side connected to the cricoid cartilage. Strictly speaking, therefore, the Cetacea have no larynx, and probably no vocal organ; and the superior part of the trachea, with the nostrils, serves merely to admit the atmospheric air for the purposes of respiration.

Birds are distinguished by possessing not only a glottis or laryngeal aperture similar to that of the Mammalia at the upper end of the trachea, but a second, denominated the inferior glottis or larynx, at the lower end, near its bifurcation. The former, which is composed of four cartilages, or six, according as the cricoid consists of one or three pieces, on the middle of the posterior part of which is a small round bone, articulated with two oblong longitudinal bones, parallel, and forming between them in the posterior wall of the windpipe a longitudinal slit, susceptible of approximation by means of muscles, is intended merely to regulate the admission of air into the windpipe, or its expulsion from that tube, and to close more or less accurately its superior orifice.

The inferior larynx consists of a membrane projecting from each side of the inferior aperture of the trachea. This aperture is divided into two, occasionally by an osseous anterior-posterior middle bar, occasionally by the angle at which the two bronchial tubes unite. Since the first bronchial arc has the same curvature as the last tracheal ring, the second and third, which are arcs of larger circles, are less convex without, but more prominent within, than the former. Over this prominence the tracheo-bronchial membrane forms a fold, which, half closing on each side the inferior tracheal aperture, forms a plate susceptible of vibrating by the motion of the air, and producing sound. This apparatus, which constitutes what is named the inferior larynx, or rather glottis, is of two kinds, one void of proper muscles, the other provided with muscles.

In the former kind of larynx the state of the glottis is altered only by those muscles which depress and elevate the trachea. The depressors are two pairs, the sterno-tracheal and the glosso-tracheal, the latter attached to the bifurcated bone and trachea. There are no proper elevators; but the windpipe is raised by the mylo-hyoid muscle through the ligaments which connect the hyoid bone to the superior larynx. In the quiescent or relaxed state, and while the trachea is depressed, the bronchial rings approximate, and the second and third even gliding below the first, the glottis may be elongated. When the trachea is elevated by these pairs of muscles, the bronchi are at the same time dragged upwards, and the second and third arcs are separated from the first; and while the external prominence of the glottidial membrane diminishes in length, its tension is augmented. These forms of larynx without proper muscles may yet be subdivided into two sorts, as they have or have not lateral pouches, membranous or osseous. These are observed in the male duck (anas) and the merganser (mergus), but never in the female; and to this perhaps the harsh and deep tone of the voice of the male bird is to be ascribed. The larynx without muscles and without pouch is observed in all the gallinaceous order without exception.

The forms of larynx provided with proper muscles may be distinguished into three subdivisions.

The first, which has only one proper muscle on each side, is observed in the whole of the falcon genus, e.g. the eagle, hawk, falcon, buzzard, sparrow-hawk, and goshawk; in the owl genus and the majority of the waders and swimmers, as the heron, bustard, woodcock, lapwing, rail, coot, gull, cormorant, and some of the passerine birds. In these birds, in which the motions of the lower larynx are necessarily limited, the voice is not variable or extensive in its notes.

The second form of larynx has three pair of proper muscles, a constrictor of the glottis, an auxiliary constrictor, and a laxator or opener of the glottis. This kind of larynx is observed in the whole of the parrot genus and psittacoid birds generally, as the toucan, macaw, calao, &c.

In the third kind of musculo-membranous larynx there are no fewer than five pair of muscles, the longitudinal levator of the demiannular cartilages, the posterior levator of the same cartilages, the small levator, the oblique levator, and the transverse levator. This quinque-muscular larynx is found not only in all the birds properly named whistlers or warblers, as the nightingale, hedge-sparrow, blackbird, thrush, goldfinch, lark, linnet, canary, chaffinch, &c., but in others whose tones are more monotonous, as the swallow, sparrow, stork, crossbill, &c., and even in some the tones of which are harsh and positively disagreeable, e.g. the jay, magpie, crow, raven, &c.

The differences remarked in the notes of these three divisions of birds with the quinque-muscular larynx depend not so much on anatomical peculiarities as on the timbre of their larynx, and on the mobility of the trachea in relation to the larynx, and on the tracheal membrane having dilatations and contractions.

On the whole, the inferior larynx of birds is to be regarded in three lights: 1st, As the reed of a wind-instrument, like a hautboy or clarionet, in which the notes vary as the lower glottis varies in its position to the windpipe; 2nd, as an instrument susceptible of uttering different tones, according to the distance between the mouth-piece and vent, or as the windpipe is elongated or shortened; and, 3rd, as an instrument capable of uttering different notes by varying the diameter of the mouth-piece, or as the superior glottis is widened or contracted.

The only bird in which the inferior larynx is wanting is the vulture.

The vocal organ of the Reptiles consists of the superior larynx only, analogous to that of the Mammalia. This is a cartilaginous apparatus, composed in general of five distinct pieces at least in the large individuals of the Saurial genera, as the crocodile and alligator, and forming a broad cavity behind, before a narrow slit, bounded by two vertical pillars. The glottis, however, is entirely membranous; and there are neither vocal chords nor ventricles. There are nevertheless two muscles, one for opening and another for shutting the glottis. When these act, and the air is made to vibrate against the anterior pillars, it gives a slight whistling sound only. In the iguana, tuipinambis, lizard, tortoise, and serpent, the arrangement of parts is nearly the same; and these animals, therefore, can utter only slight hissing sounds. In the chameleon the pillars are furnished with a tense, vibrating membrane, a fleshy tubercle which contracts the glottis, and a membranous pouch opening below, between the lower laryngeal cartilage and the first tracheal ring. In the frog tribe, so remarkable for their croaking noise, the vocal chords are large and prominent. The males have also two membranous pouches, opening by a small aperture, not in the larynx, but deep in the lateral part of the mouth. When the frog croaks these pouches are inflated, and swell the skin on each side below the ear. Though these sacs are wanting in the female frog, and toad both male and female, as well as the tree-frog, there is beneath the throat a single pouch on the median plane. A general view of the nervous systems in different classes of animals shows that the only common part is an axzygos tubercle, situate at the anterior extremity of the spinal chord, connected by means of two lateral bundles or peduncles to the rest of the system. This mass, which corresponds to what is denominated the cerebellum in man, is connected in the vertebrated red-blooded animals with several pairs of tubercles, forming generally a larger mass than itself, and connected to the rest of the system by two longitudinal bundles or limbs, which mingle with and intersect those of the cerebellum. These anterior-superior tubercles, which constitute the brain proper, present numerous modifications in figure, disposition, and magnitude, and even in presence, in the different orders of the animal world.

In the vertebrated animals the brain or central part of the nervous system consists of the vertebral or funicular portion, named the spinal chord, and the cranial or cephalic portion, properly denominated the brain.

The funicular portion has the shape of a cylinder flattened on its superior or dorsal and inferior or sternal surfaces. It consists of two similar chordiform productions, united on the mesial plane, and marked at the line of junction by linear longitudinal furrows, of which the superior is most deep and distinct. This, however, which was observed by Blasius in several animals, is denied by Bellingeri, who asserts, from various observations, that though in some parts the superior furrow penetrates more deeply than the inferior, in the general course of the chord the latter is the deepest. (De Medulla Spinali Annotationes Anatomico-Physiologicae. Auctore C.F. Bellingeri, Aug. Taurinorum, 1823.) This discordance appears to depend on the circumstance that the sternal or inferior furrow is in truth deeper and more distinct in man, the monkey tribe, and a few Mammalia, than the dorsal; whereas in most others, as the coati, raccoon, horse, &c., the dorsal furrow is of the same depth as the sternal; and in the mole, murine, and leporine genera, it is deeper and more distinct than the sternal. In Birds and the cartilaginous Fishes the sternal furrow is deepest; in Reptiles the dorsal and sternal are nearly equally deep; and in the osseous Fishes the dorsal is the deepest. On each side of the chord also, there is a slight longitudinal depression commonly called the lateral (sulcus lateralis).

The breadth and thickness of the spinal chord vary in different regions. The lower cervical portion is in general the broadest and thickest; at the upper dorsal region it is somewhat more slender, becoming thicker again at the lower dorsal region; and after again becoming more slender in the lumbar region, it is expanded into a filamentous brush-like termination of different lengths in different classes, and even in different orders. These enlargements at the superior dorsal and lumbar regions are believed by Serres to correspond with the origins of the thoracic and pelvic extremities; and each swelling he represents to predominate over the other, as the animal habitually employs the one or the other kind of members. It is remarkable in illustration of this principle, that in the Cetacea, which are void of pelvic extremities, the lumbar enlargement is wanting; and in the amphibious Mammalia, the pelvic extremities of which are feeble, this enlargement is also inconsiderable.

The spinal or funicular brain consists of white cerebral matter on the surface and gray matter in the centre, the former being most abundant, unless in the sacral region, where both are nearly equal in quantity, or the gray rather predominates. In the Mammalia the gray matter is in greater proportion to the white than in the other three classes, in which the white matter progressively augments.

The sternal and dorsal longitudinal lines indicate the original formation of the chord in two lateral portions, with an intermediate cavity denominated the spinal canal. This exists only during the formation of the chord in the human fetus, in some of the Mammalia when adult, and in the other three classes. Its disappearance in the human fetus, and in that of various Mammalia, is represented by Serres to depend on the progressive deposition of gray cerebral matter on the inner or central surfaces of the component pillars of the chord. Though obliterated in man, in whom the gray matter is abundant, it is not hermetically sealed in the monkey tribe, in which some traces of it are left. In the Amphibia and Cetacea it is larger than in the monkey tribe; its diameter augments in the Carnivora, feline, canine, and ursine, in which the gray matter is thinner than in the former; and in the Rodentia it is said to be largest of all among the Mammalia. Lastly, in the birds, reptiles, and fishes generally, in which the gray matter is scanty and the white predominates, the spinal canal is large and distinct.

The lateral regions of the spinal chord are connected with a double series of nerves by means of two rows of nervous filaments, an anterior and posterior, separated by a longitudinal membrane of fine white tissue, with a serrated or festooned border. This membrane, which is named the denticulate, is the same in the Mammalia and Birds. That these nerves do not issue from the spinal chord, must be inferred not only from the phenomena attending the original development of the nervous system, but especially from what is observed of their comparative size, and that of the chord in the inferior classes. In that of fishes especially, while the chord is small and slender, and by no means fills the vertebral canal, it is remarkable that the nerves which supply the voluntary muscles are exceedingly large. Thus, in many both of the cartilaginous and osseous divisions, as the sturgeon, dog-fish, ray, wolf-fish, cod, &c., the nerves which supply the pectoral fins are large, broad chords, two or three of which seem to contain more substance than the whole spinal chord itself.

The chord is expanded at its cephalic end into a thick bulb of the eminence denominated the spinal bulb, the surface of chord, which presents three pairs of eminences. These eminences are developed in various degrees in the different classes and orders. In some of the Mammalia the anterior pyramids or pyramidal bodies are more distinct than in man, for instance the ape tribe, the Cetacea, Carnivora, Ruminants, and Rodentia. They are small in most Birds, all the Reptiles, and the Cartilaginous Fishes. In the osseous division they assume the appearance of two parallel chords at the base of the brain. The olivary bodies, less prominent in the ape than in man, are still less so in the Cetacea, and progressively through the Amphibia, Carnivora, Ruminantia, Rodentia, and Insectivora, and the other three great classes of vertebrated animals. Conversely, the restiform bodies or posterior pyramidal eminences, from man through the ape tribe, the Cetacea, Amphibia, to the Ruminants, Carnivora, and Rodentia, increase in size.

Though the brain of the Mammalia presents the same parts, and is arranged nearly in the same order, as that of man, it varies in its proportions to the rest of the body; in its proportions to the cerebellum and spinal bulb; in general figure; in the presence, absence, and number of convolutions; in the configuration of its central surface; in the communication of its central with its external surface; and in the manner of its connections with the cerebral nerves. As it is impossible in this sketch to examine all Comparative Anatomy.

These circumstances fully, we shall confine our attention to the notice of a few only.

It is not easy to ascertain the proportion of the mass of the brain to that of the rest of the body. Excluding as much as possible the ordinary sources of fallacy, in small animals the brain is proportionally larger; yet in this respect man is surpassed only by a small number of animals, habitually lean, and with little muscle, as bats, small birds, &c. While the proportion of brain in man to that of the whole person varies from a 22d to a 35th part, that of the monkey tribe varies from a 22d to a 42d part; and in the baboon it is only the 104th part of the body. Among the Mammalia, the Rodentia have in general the largest proportion of brain, and the Pachydermata the smallest; and while the hare has a brain about the 300th part of the size of the body, that of the elephant, the most sagacious of animals, is about the 500th part the size of his body. It is also remarkable, that while the brain of the horse is only a 400th part of the size of his body, that of the ass amounts to a 254th part. The Reptile brain becomes excessively small, that of the turtle being rather more than the 5000th part the size of his body; and in some of the Fishes, not all, it appears to attain the maximum of decreasing proportion, that of the tunny being so small as the 37,000th part of his body, while the brain of the carp is so large as to approach the proportion of the elephant. It may be doubted whether, under such circumstances, any precise conclusions can be drawn from results so variable and so little to be expected.

The proportional weight of the brain to that of the cerebellum is, excepting in the case of one species of ape, the saimiri, greater in man than in any other animal. The ox is equal to man in this respect, and the dog approaches him. The animals most remote are the Rodentia, as the beaver, rat, and mouse, &c.

The convolutions, which are so numerous and so deep in man, diminish both in number and size in the Quadrupedina and Carnivora, and are nearly obliterated in the Rodentia. In the Ungulated animals, however, and especially in the Ruminants and the horse, the convolutions are numerous; and even in the dolphin among the Cetacea, they are numerous and deep. In all the Mammalia the cerebellum is foliatted.

On the whole, the peculiar character of the brain of man and the ape family consists in the existence of the posterior lobe and digital cavity. The brain of the Zoophaga is remarkable for the small size of the nates or anterior pair of the bigemious eminences in proportion to the testes or posterior pair. In the Rodentia the organ is distinguished for the large size of the nates, and the want or superficial nature of the convolutions. In the Ungulated division of animals, i.e., Pachydermata, Ruminantia, and Solidungula, the brain is remarkable for the large size of the nates combined with the number and depth of the convolutions; while that of the Cetacea is remarkable for its height and breadth, and the want of olfactory nerves. It is further to be observed as a general distinction between herbivorous and carnivorous or zoophagous animals, that in the former the nates are larger than the testes, whereas in the latter the testes are largest. Lastly, Man and the Quadrupedina are the only animals which possess genuine olfactory nerves. In the other quadrupeds they are represented by the mammillary processes of the ancients; and in the Cetacea they have not yet been unequivocally demonstrated.

The brain of Birds is at once recognised by consisting of six distinct tubercles, two representing the cerebral hemispheres, two representing the optic eminences, one the cerebellum, and one the bulb of the chord. The hemispheres are void of convolutions, but the cerebellum is marked by transverse parallel striae corresponding to the laminae of the mammiferous brain. There is neither middle band (corpus callosum), vault, nor septum. The ceiling or vault of the aqueduct or passage from the third to the fourth ventricle is not, as in the Mammalia, surmounted by the bigemious eminences, but is merely a thin plate corresponding to the valve. Each optic eminence contains a cavity communicating with the others by the Sylvian aqueduct. The anterior eminences (corpora striata) are not striated with alternate white and gray matter, as in the Mammalia. Between the anterior and the optic eminences are four rounded tubercles, best seen in the ostrich, which are to be regarded as entirely heterologous to the structure of the mammiferous brain, and connecting the cerebral structure of Birds with that of Reptiles and Fishes, in which also these tubercles are observed.

The Reptile brain is smooth and unconvoluted. The optic eminences, which are situate behind the hemispheres, are uncovered, and contain a ventricle communicating with the third. At the extremities of the latter are the anterior and posterior commissures, but there is neither soft commissure nor bigemious eminences. The hemisphere presents an anterior eminence, which, however, in the brain of Birds is unstriated. The cerebral valve is, like that of Birds, unsurmounted by bigemious eminences.

In the class of Fishes the structure becomes still more simple. The tubercles of which the brain consists are placed in a row; and their increase in number only demonstrates the decomposition of the organ, and its resolution into simple integrant parts. The two representing the hemispheres are ovoidal, unconvoluted, and contain a ventricle, in which is seen the eminence analogous to the striated bodies. The optic eminences, situate beneath the hemispheres, though small, contain each a cavity, as in the two oviparous classes already noticed. Lastly, there are in several genera, under the common vault of the hemispheres, occasionally two, occasionally four tubercles, variable in shape and proportions, but which would be analogous to the bigemious eminences, were they not, like those already mentioned in Birds, situate before and above the optic chambers. In the cartilaginous fishes, in which these tubercles are not observed, the anterior or striated eminences are obliterated. The cerebellum does not cover the fourth ventricle.

Behind the cerebellum are two tubercles, which in the ray give origin to the fifth pair, and are very distinct in the pike, trout, salmon, and perch. These tubercles are peculiar to this class.

The cavities in the interior of the optic eminences in Birds, Reptiles, and Fishes, are observed in the fetal brain of the Mammalia during its early growth.

It is almost superfluous to mention, that, in the two warm-blooded classes, Mammalia and Birds, the brain, with its investments, fills completely the cranial and vertebral cavities. In the Reptiles, however, in which the brain does not approach the cranial walls, we remark the first departure from this arrangement; and in the Fishes it is so completely violated that the brain and chord occupy but a small proportion of the cranio-vertebral cavity; and between the former and the osseous walls there is a quantity of fine but very loose filamentous tissue, containing in its cells a large quantity of pelucid fluid. Though this arrangement gives this the appearance of a white jelly-like substance, it is not gelatinous, as is generally represented, but merely a pelucid fluid, sometimes pale straw-coloured, occasionally with a reddish tint, contained in numerous communicating cavities of a tissue which appears to represent the arachnoid of the warm-blooded animals. The pia mater in the reptiles and fishes is reduced to a filamento-vascular web, accompanying the blood-vessels.

The dura mater undergoes some peculiar modifications in different orders. In the duckbill a bony plate is contained between the laminae of the falx; and the same structure is found in the porpoise, perhaps in the other Cetacea. An osseous tentorium with a quadrangular aperture is found in the coatis and marten, and the feline and ursine families; and an osseous partition consisting of three parts is found in the dog, horse, Cape ant-eater (orycteropus), the wombat, and the seal. The bony tentorium is also found in the woodcock and others of the feathered class. In the red but cold-blooded animals the dura mater forms neither falciiform nor tentorial process.

On the nerves or ramified chords of the nervous system a few words must suffice. In fishes the tenth or pneumogastric consists not of a common trunk, but of three orders of filaments, the first and largest of which are distributed to the gills, and correspond to the pulmonary nerves of the Mammalia; the second, slender, are distributed to the muscles of the tongue and the surface of the oesophagus; and the third terminate in a large nerve which traverses the body longitudinally immediately beneath the lateral line. The phrenic nerve is wanting in birds, reptiles, and fishes.

In the Mollusca the nervous system consists of a number of whitish cerebral masses distributed in different parts of the body, with one or two more conspicuous than the rest, and supposed therefore to represent the brain, placed transversely over the oesophagus, which it encompasses with a nervous collar.

In the Articulata the nervous system consists of two long chords extending along the belly, and expanded at various intervals into gangliform knots or enlargements. The first of these, which is situate on the oesophagus, rarely exceeds the others in size. Among the Zoophytes hitherto examined the nervous system assumes either a radiated or an arborescent form.

PART II.

COMPARATIVE ANATOMY OF THE ENTROPHIC ORGANS.

CHAP. I. THE LIMITROPHIC ORGANS.—SECT. I.

THE ORGANS OF DIGESTION.—§ 1. THE TEETH.

Though genuine teeth are found in three classes of animals only, viz. the Mammalia, the Reptiles, and the Fishes, yet all the orders of these classes are not provided with teeth. Thus, among the first class, the ant-eater tribe, the pangolin, the echidna and ornithorhyncus, and the whales—among the second the chelonians—and among the third the sturgeon—are altogether destitute of these organs. In all the invertebrated classes, the jaws, when present, are provided with notches varying in number. The echidnoderma alone have genuine teeth, inserted in a mechanical apparatus very different from ordinary jaws.

Though in general structure the teeth of the lower animals resemble those of man, in some respects they differ considerably. These varieties consist either in some change or modification of the constituent parts of the teeth, or in the addition of some other substance to those parts.

The first variety to be noticed is of the former description.

Though in the Quadrupeds and Zoophaga the bony matter of the teeth is quite similar to that of man, in other orders this substance appears in the form of a very hard, compact, and more regularly fibrous substance than bone, and to which the name of ivory (dub) is applied. It is chiefly in the canine or tearing teeth that this substance is found to represent the bony pillar of the teeth; and it is principally among the Pachydermata, and some of the Amphibia and Cetacea, that this change is observed.

The ivory of the elephant is the most tender, and that which most rapidly becomes yellow on exposure to air. It is readily distinguished from the ivory of other animals by the curve lines which radiate from the centre to the circumference of the tooth in various directions, and which form by intersection regular curvilinear lozenges.

The ivory of the hippopotamus is greatly harder and whiter, and is on that account preferably employed for the preparation of artificial teeth. A transverse section of this substance shows striæ extremely delicate and regular. In this animal, also, not only the canine but the incisor teeth consist of this substance. The tusks of the Ethiopian boar (sus ethiopicus) consist of ivory similar to that of the hippopotamus. In those of the ordinary boar, though no striæ are recognised, there is sometimes a mixture of brown substance disposed in layers. The ivory of the teeth of the morse, though void of striæ, is compact and susceptible of polish nearly as brilliant as that of the hippopotamus; and its character is, that the central pillar of the tooth consists of minute round grains, indiscriminately aggregated, like pebbles in puddingstone. The axis or pillar of the molar teeth of this animal, which are without internal cavity, consists of similar minute grains. The ivory of the dugong is homogeneous and without striæ. That of the teeth of the white whale or cachalot resembles the bone of human teeth in its satin-like appearance. The ivory of the tusk of the narwal is very compact and homogeneous in appearance.

The most singular structure of teeth among quadrupeds is observed in those of the Cape ant-eater (orycteropus). The teeth of this animal, which have the appearance of two cylinders conjoined, consist of an infinite number of minute straight parallel tubes, so that their transverse section resembles that of a rush. As these tubes are closed only at the triturating surface, it is there only that the tissue of the tooth is compact; and when the enamel is worn, the upper orifices of these tubes begin to be exposed. There is, therefore, no general cavity in the interior of the tooth. These teeth are also void of root. A similar tubular structure is observed in the two molar teeth of the ornithorhyncus, and in the teeth of some fishes.

The enamel (lamella citrea, cortex striatus) presents Enamel peculiarities in the lower animals, as well as the bone of the tooth.

While the enamel of the human tooth is confined to the crown, in several of the lower animals, as the morse, it envelopes the tooth all round; and in the molar teeth of this animal, which, indeed, are void of cavity, it is thicker under the root than at the crown. A similar arrangement is observed in the old or adult teeth of the cachalot, which, when their cavity is obliterated by the full deposition of osseous substance, are also covered with enamel below.

The texture or constitution of the enamel is best seen in the grinders of the elephant. The section of a tooth in the germ exhibits fibres similar to those of asbestos or fine velvet. The fracture of the enamel is more distinctly fibrous than that of the bone, and the fibres are everywhere perpendicular, or nearly so, to the surface of The hardness of this substance may be inferred from the fact that it strikes fire with steel. These component fibres, however, are not always rectilineal. Most frequently they describe curves with the convexity of incursion towards the crown and the concavity towards the root. This arrangement at least is observed in the ruminants. The distinction between the enamel and bony matter is recognised by a gray line, and another whiter which belongs to the latter substance.

The enamel varies chiefly in thickness in different animals. The tusks which project from the mouth are generally observed to be less white, less hard, and more similar to bone or ivory than the other teeth; and on this account, probably, the existence of enamel has been denied in the tusks of the elephant. It is nevertheless certain that the external layer of these tusks presents radiating fibres, though it is by no means so hard, or possesses the same grain, as the enamel of the other teeth. Enamel is more apparent, though thinner, in the tusks of the morse, dugong, and boar; and it is quite as distinct in those of the hippopotamus as in the other teeth of that animal. Lastly, the enamel of the teeth of the cachalet, which is very thick, shows in its section only striae parallel to the surface of the osseous substance.

Teeth may be distinguished according to the mode in which their component tissues are arranged into three sorts. 1st, When the enamel invests the axis all round, and does not penetrate the latter, the tooth is said to be simple (dens simplex). Such is the character of the human teeth, and those of the Quadrumanana and Zoophaga, and several other animals, and all the reptiles.

2nd, When the enamel is folded as it were round the bony part, but without inclosing it, so that the latter forms a continuous band several times folded on itself, and sections of the tooth in every direction divide repeatedly the component substances, the tooth is said to be compound or complex (dens multiplex vel compositus). A good example of this structure is seen in the grinders of the elephant.

3rd, When the base or root of the tooth is simple, and the folds of the enamel and bone penetrate only to a certain depth, they are said to be semicompound. Examples of this modification of arrangement are seen in the grinders of the ruminating animals.

In the compound, and part of the semicompound teeth, the enamel is covered by a third substance; and as the latter is arranged, especially in the former sort, so as to leave intervals between it and the next layer of enamel, this substance serves to fill all these intervals, and consolidates the component lobes of the tooth even before their osseous parts are united below. This substance, which is denominated by Cuvier cement, by Tenon cortex ossaeus, and by Blake crusta petrosa, though less firm than either bone or enamel, is dissolved by acids more slowly than the former, and sooner becomes black in the fire. In the teeth of the elephant and cabiai it forms half their mass at least. In most genera it presents no apparent organization, and resembles a sort of crystalline tartar incrusted on the tooth. In the cabiai, however, it presents numerous pores very regularly arranged. Tenon was of opinion that it arose from ossification of the membrane which enveloped the tooth; Blake ascribed it to deposition from the opposite surface of the enamel membrane; but Cuvier ascertained that it is deposited by the same membrane and the same surface as the enamel. This accurate observer found, on inspecting the germs of the teeth of the elephant, that when the internal membrane of the dental capsule has deposited the enamel, it undergoes a change of structure, and becomes thick, spongy, opaque, and reddish, to furnish the cement, which is then deposited, not in regular crystalline fibres, but in random drops.

The teeth of the Reptiles consist of hard, compact, osseous matter, invested by a thin covering of enamel, and without cement.

The teeth of Fishes vary much in structure. They are Teeth of either simple or compound. The simple teeth are those fibres which consist of bone invested by enamel. They may be distinguished into two species, according to their mode of attachment. The first are the simple teeth, which are not implanted in alveoli, but merely attached to the gum, or fixed by articulation to the jaw, as those of the shark tribe; the second are simple teeth growing in alveolar cavities, as is observed in the majority of fishes, the pike, dory, &c. The simple teeth attached to the gum are chiefly distinguished by their fibres intersecting in the manner of the cancellated tissue of bones, and being therefore at first light, porous, and spongy, and becoming afterwards uniformly hard and compact like ivory.

The compound teeth, which consist of an infinite number of minute tubes mutually aggregated and invested by a common covering of enamel, form plates of different sizes, adhering to the bones of the jaws or palate by an intermediate membrane only. In some they affect the disposition of the quincunx; in others they occupy the whole breadth of the upper jaw at least, as in the ray as seen on the small scale, and in the same manner in larger fishes; others are in straight transverse bars; others assume the shape of a circular segment, or the figure in heraldry denominated the chevron.

In the wolf-fish the jaws are provided with eminences composed of fibres or tubes proceeding from the base to the circumference, and which are connected to the jaw by a substance more spongy than the rest of the bone.

After their first formation the teeth retain nearly their original shape in the Zoophaga, man, and the Quadrumanana. In the two latter only their crowns begin to be worn, rendering the incisor and canine less pointed by the use of food partly vegetable; but in the zoophagous tribes they undergo no detrition whatever. In the herbivorous animals, however, the crown begins to undergo detrition more or less rapidly; and in no long time the superior layer of enamel is entirely worn off, and the surface of the tooth exposes the succession of bone or ivory, enamel, and cement. These substances are well seen in the teeth of the Rodentia, for instance the hare; those of the Pachydermata, as the elephant; the Ruminants, as the stag, sheep, and ox; and the Solitudinula, as the horse. In all these animals the enamel, which is hardest, forms prominent lines or ridges; while the bone and cement are indicated by depressions.

This detrition, which is purely mechanical, might proceed to such an extent in the herbivorous quadrupeds as to destroy the whole of the crown of the tooth, and leave the process of mastication to be performed by the jaws only. It appears to be chiefly to obviate this inconvenience that the dentition of the elephant, the Ethiopian Successor boar, and perhaps all the Pachydermata, is conducted in a successive manner through a series of six or eight sets of teeth at least. In the former animal, in which this process has been best observed, and was ably explained many years ago by Mr John Corse Scott (Phil. Trans. 1799), each half-jaw, whatever it contains, exhibits at one time only one complete grinder and part of another behind it, the prominent parts of which are placed obliquely to the horizon, forming an inclined plane, so that the anterior parts are worn before the posterior. The anterior complete one, which is employed in mastication, undergoes progressive detrition till its anterior portion is worn down to the level of the jaw. In this state the fangs of the anterior part of the tooth begin to diminish, rendering the tooth narrow before; while the crown of the poste-

Comparative Anatomy.

The posterior begins to be worn, and undergoing the same detrition, the posterior fangs also begin to give way. While this process, however, is advancing, the posterior tooth, of which only the anterior part was appearing above the gum, gradually rises, with its crown forming a plane inclined from before backwards, similar to that of the anterior grinder. When this posterior tooth has been raised sufficiently to allow its anterior margin to be used in mastication, the residue of the anterior tooth drops out altogether, and the posterior one continues to rise and advance rapidly, until it is completed, when it is found to be much larger than the previous tooth, and to consist of a greater number of plates of ivory and enamel (denticle). In no long time this new tooth, which undergoes the same process of detrition, is succeeded by another one, the anterior margin of which rises first behind the posterior one of its predecessor, and which passes through the same stages of growth, detrition, and shedding. This process is repeated at least seven or eight times, and each succeeding tooth is larger, and contains a greater number of ivory and enamel plates than its predecessor. The elephant has thus 7 or 8 grinders in each half-jaw, or 28 or 32 grinders respectively; yet there are never more than one tooth and part of another, or at most two, that is, eight teeth in the upper and lower jaws, at the same time. Though the disappearance of the fangs of the anterior tooth is ascribed to absorption—which indeed is a good general name—yet the true reason is the fact that the maxillary or dental vessels of the elephant are unable to sustain more than one tooth in each half-jaw at once; and that since these vessels gradually transfer their blood to the new tooth, while those of the old one shrink and are obliterated, as the new tooth grows the old one is actually dehematized or atrophied. The order in which the teeth of the elephant succeed each other is nearly the following. The first or milk grinder, composed of 4 eburne-vitreous plates (denticle), cuts the gum eight or ten days after birth, is well formed in six weeks, and completely out in three months. The second, which consists of 8 or 9 plates, is completely exposed at the age of two years; the third, consisting of 12 or 13 plates, at six years. The fourth to the eighth grinder consist of plates varying in number from 15 to 23; but the period at which these teeth appear has not yet been determined. This process has been shown to have taken place also in the gigantic fossil animal named the mastodon.

A similar process of displacement and renovation takes place in the poison-teeth of serpents, and in the teeth of the shark, diodon, and tetraodon tribes. In the wolf-fish (anarrhicus lupus) the teeth are shed along with the spongy membrane in which they are contained, exactly as the horns of the stag.

In the horse, in which the process of dentition has been carefully observed, it is usefully employed to determine the age of the animal. The milk incisors appear at the end of 15 days; the four middle ones, or the nippers, are shed at 30 months; the four following ones at 42 months; and the four external, or the corner teeth, at 54 months. The permanent corner teeth do not grow so quickly as the other incisors; and by these especially the age of the horse is determined. At first they scarcely rise above the jaw. Their middle then presents a hollow filled with blackish tar, the margins of which are worn down as the tooth rises from the gum, and is rubbed against the corresponding one; and it diminishes progressively from 54 months to 8 years, when it is altogether obliterated. The hollow of the other incisors is obliterated at a later period than that of the corner ones; and the age of the animal is then estimated from the length of the incisors, which continue to increase.

The first two molar teeth appear in each jaw and on each side about the 8th day, the next at the 20th, and the complementary or small anterior grinder about the 5th or 6th month. The first posterior molar appears about the 11th month, and the second in the 20th. At the 30th or 32d month the first two milk grinders are shed, the third in the 3d year; and about the 5th or 6th year the last posterior grinder appears. The milk grinders are longer from before backwards than the permanent ones, which are themselves contracted in this direction, as they are pressed by the posterior grinders; from which it results that the dental crowns of young horses are oblong, while those of the old are quadrangular.

In the Mammalia the teeth are always implanted in the jaw-bones, and never, as in other animals, in the tongue, palate, &c. The only exception to this rule is the echidna.

The three kinds of teeth, incisor, tearing, and grinder, are found together only in Man, the Quadrupedana, the men of Zoophaga, the Pachydermata except the elephant, the teeth and two-horned rhinoceros, in the hornless Ruminants, and in the Solidungula; but, of all these animals, in man only are the three forms of teeth arranged in an uninterrupted series, and in such a manner that those of the lower jaw are applied to those of the upper. In one other animal only, now extinct, the anoplotherium, is this continuity of arrangement observed.

In the Quadrupedana and Zoophaga, and all those in which the canine are larger than the other teeth, there is a gap on each side of the jaw to receive the canine of the opposite one. In the ursine genus there is a large empty space behind each canine tooth. In the hedgehog, shrew, phalanger, and tarsier, in which the canine are shorter than the other teeth, a space is left between them and those opposite. In the maki tribe, proper bat, colugo, and camel, there is a large interval between the upper incisors. Lastly, the Ruminants want the incisors of the upper jaw, and the morse those of the lower.

Some animals provided with the three classes of teeth lose the incisors at a certain age; for instance several of the bat tribe, and the Ethiopian hog. Other Mammalia have only two sorts of teeth, for instance incisors and grinders, separated by an interval without canine, as the wombat and all the Rodentia, in which there are only 2 incisors in each jaw; the kangaroo, which has two below and 6 or 8 above; and the cavy or hyrax genus, which have 2 above and 4 below. The elephant has grinders and two tusks planted in the superior intermaxillary bone, but no inferior incisors or canine teeth.

Animals may possess grinders and canine teeth without incisors, as the sloth tribe and the dugong. The grinders, which are most essential, are most rarely wanting; and when others are deficient these are present, as in the armadillo tribe, the orycteropus, the ornithorhyncus, two-horned rhinoceros, and lamantin. The jaws of the dolphin are provided with uniform conical teeth all round, while the cachalot or white whale has them in the lower jaw only. In the narwal there are only two long spiral tusks implanted in the intermaxillary bone, and of these one is often wanting.

Lastly, teeth are entirely wanting in the ant-eater tribe, Absence of pangolin, and echidna, which are therefore arranged among the teeth, the Edentata. In the whale the teeth are represented by plates of the laminated, fibrous, bluish substance distinguished by the name of whale-bone.

§ 2. ORGANS OF INSALIVATION.

Under this head ought to be noticed the modification which the salivary glands undergo in the lower animals. Our limited space, however, obliges us to proceed immediately to notice the peculiarities of the other divisions of the alimentary canal. § 3. OESOPHAGUS, STOMACH, AND INTESTINAL TUBE.

The muscular tissue of the oesophagus consists, in most of the Mammalia, of spiral fibres twisted in two opposite directions, the external from before backwards, the internal from behind forwards. This arrangement, which was first observed in the Ruminantia, was supposed to explain the process of rumination. This opinion, however, is refuted by the fact that the arrangement is not confined to this order, but is very general among the zoophagous and other animals which do not ruminate. In the kangaroo the direction of these fibres is, as in man, transverse in the internal layer, and longitudinal in the external.

The oesophageal mucous membrane is covered by epidermis, which extends to the cardiac opening of the stomach in man, the Quadrumania, and all the Zoophaga. This membrane, as well as the mucous, is thrown, by the action of the muscular tunic, into longitudinal folds, which are effaced only when the oesophagus is distended. In the tiger, lion, and lynx, there are large transverse valvular folds, and smaller ones in the civet and cougar—an arrangement connected probably with the carnivorous habit.

The stomachs of the lower animals vary considerably in shape, in the insertion of the oesophagus, in the disposition of their muscular tunics, and in the simplicity or complication of their cavities. These characters it is impossible in such a sketch as the present to consider in detail; and we shall confine our attention to those peculiarities which are most striking in the digestive organs of the animal world.

The stomachs of the Mammalia may be distinguished into the simple and compound. Those of man, the Quadrumania, zoophagous and most of the herbivorous tribes, belong to the former order. This simple form of stomach, however, may be generally distinguished into two parts, a cardiac and a pyloric, more or less separated from its other by a central transverse contraction of its annular muscular fibres. This is particularly seen in the horse, man, murine family, and many other animals which occasionally feed both on animal and vegetable matter. In the human stomach this contraction is represented in Plate XXXVI. fig. 4. In the porcupine, however, there are three pouches. This contraction depends on a strong annular band of muscular fibres at this part of the organ. In the pure carnivorous animals, however, as the feline family, the annular fibres, which are very thick, are nearly equally so from the cardiac to the pyloric end.

The compound stomachs, or those which contain more cavities than one, are found in the sloths, and the ruminant and cetaceous animals chiefly.

In the first tribe the stomach of the Uman, or two-toed sloth, is two-fold. The first cavity is large and globular, but tapering behind into a conical appendage, separated by a semilunar fold; while a large cul de sac on the left of the cardia opens into a canal which proceeds at first backwards, and then turning to the right, enters the second cavity by a narrow aperture. The second, which is small, tubular, and folded under the former from left to right, is distinguished by a semilunar fold into two halves, the first of which opens into a small cul de sac on the right side of the first cavity. The inner membrane of both cavities is smooth, and without villi. A similar arrangement is found in the Ai, or three-toed sloth, with this exception, that the appendage of the second gastric cavity is divided into three compartments by two longitudinal bands. This canal seems analogous to the arrangement of the ruminating stomachs, in so far as it may allow the alimentary matters to pass occasionally from the oesophagus directly into the second stomach.

The stomach of the hyrax, ashkoko, or Cape cavy, also consists of two pouches, separated by a middle partition, in which there is an aperture for mutual communication. In the hippopotamus the cardia communicates with three pouches, two of which are cognizable without, and with a long tubular bowel, the interior of which is divided across by several valvular folds.

In the kangaroo the stomach receives the oesophagus near its left extremity, which is small and bifid (Plate XXXV. fig. 8); and forming a larger cavity on the right, passes upwards, making a turn, and crosses to the left before the oesophagus, makes another turn, and again crosses the mesial plane to the right, where it terminates in a tapering cavity at the pylorus. In this course it presents internally a longitudinal band (L, L, L), extending all round to near the pyloric end, and crossed by valvular membranous folds, which divide the cavity into cells not unlike those of the colon, especially in the horse. The mucous epidermis is continued from the oesophagus over the space marked c, c.

The stomach of the Ruminants consists of four distinct quadrilobed communicating cavities. The first, denominated the cardia, is a large bag occupying the left side of the rumen, abdomen chiefly, marked externally by two saccular appendages, and separated within into four parts. (Plate XXXV. fig. 1, A, A, A, A.) Its inner surface, upon which the epidermis is continued, is occupied by flat papillae. By a pretty wide aperture (n, n), with rounded margins, this communicates with the second cavity named the Kingswood (καρδιοπάχες, reticulum, le bonnet), which is distinguished by the rhomboidal and polygonal cells, into which its inner membrane is moulded. An aperture at the further end of this (c) leads into the third or smallest cavity, termed the Manplies (γύμνος, omasum, le feuillet), from the numerous concentric crescentic folds formed by its inner membrane (fig. 2, e and p). These folds amount to about 40 in the sheep and 100 in the ox. The smallest of them, between the aperture from the second into the third cavity, are puckered or collected towards their further end by a transverse membranous fold, which acts as a valve to the aperture between this and the fourth cavity. This one, generally named the Red (γύμνος, abomasum, la caillette), is of an elongated pyriform shape, slightly incurved on itself (fig. 2, d), and is marked internally by longitudinal folds (p) incurved according to the curvature of the cavity itself; and terminating near the pyloric end in rugae or irregular duplicatures (r). This is the structure of the gastric cavities in the ox.

In the camel, dromedary, and lama, the stomach is equally complicated, though the structure is a little different. In the first of these animals, which may be taken as an example of the others, the Paunch or first cavity is a large bag, divided into two compartments on the posterior part, by a strong band passing from the right side of the cardiac orifice longitudinally downwards (L, L, fig. 3), and forming one border of a groove leading to the orifice of the second. From the left margin of this band proceed eight muscular bands, nearly at right angles, and intersecting with others, form cellular cavities on the left side of the paunch (s); while on the right side there are similar cells, though smaller, and wholly unconnected with the longitudinal band. From the left margin of the cardia, in like manner, proceeds a broad muscular band (m, fig. 3) to the aperture (a) of the Paunch into the Kingswood, after which it takes another direction (m, fig. 4) towards the Manplies or third cavity, within the orifice of which it terminates (c, fig. 4). The Red or fourth chamber is much the same as that of the bullock (d, p, b, fig. 5), and the only peculiarity is, that after terminating in (II) the pylorus, it opens in a small cavity (o) which leads into the duodenum (Δ). From this description, for the particulars of which we are indebted to the accurate account of Sir E. Home, it results that the stomach of the camel differs from that of the ox and other horned ruminants chiefly in the possession of the quadrilateral cells in the second stomach. Into these the water is conveyed by the animal when drinking, and in these it remains. By the action of the muscular band (m), the aperture between the Paunch and Kingshood is opened, and the water is directed into it so as to fill its cells. When these are filled the surplus runs off into those of the first stomach, where at least those on the left side of the long band may be regarded as part of the general cellular structure. These cells are represented of a large size in fig. 5, in which they appear like oblongs with rounded corners. They are always larger on the left side of the band, in the Paunch, than those in the second stomach.

Both in the bullock and in the camel, and in all the Ruminants, the first and second stomachs only are covered by mucous epidermis.

In the Cetaceous animals similar complication of the gastric cavities is observed. In the bottle-nose porpoise, which may be taken as an example, the oesophagus, which is large and capacious, terminates in a spheroidal or oval flask-like bag (fig. 6, a, a) with an aperture a little below the cardiac, consisting of rose-like annular folds, and leading into a second cavity. This, which corresponds to the ruminant kingshood, is nearly spherical in shape (fig. 7, n), and presents valvular folds more circular than in the ruminants, and intersected by others so as to give it the honeycomb appearance characteristic of this cavity. From this another aperture leads into the smallest cavity of the three (c, fig. 7); and thence into the fourth, which is long, cylindrical, and slightly incurved. The third cavity is remarkable for presenting in its inner membrane numerous apertures of mucous glands.

Birds are distinguished by possessing a stomach consisting of three cavities. The first is the crop, which may be regarded as a mere expansion of the oesophagus, and confined chiefly to land birds. It is filled not only with food, but with small stones; and its chief purpose seems, by mechanical comminution, to supply the place of the teeth in dividing the granular aliment, and bruising or killing the animals swallowed. It is found chiefly in the granivorous birds. It is wanting in the ostrich; in the piscivorous birds, and most of the GALLIFORMES.

The second is the glandular crop or subsidiary stomach (ventriculus succenturiatus, bullbus glandulosus), a membranous-glandular sac, which may be also regarded as an oesophageal dilatation. It is larger when the crop is wanting; and though, when conjoined with it, it is always very glandular, and may be therefore regarded as a chemical solvent of alimentary substances, it appears to supply the want of the crop, which is certainly chiefly a mechanical apparatus. The glandular crop or subsidiary stomach is remarkable for the number and size of the glandular bodies contained between its mucous and muscular tunics. These glands, though variable in shape, are generally conical; and some consist of several glands conjoined in one common peduncle (Plate XXXVI. fig. 3). All of them are hollow, and secrete a fluid which is discharged by one or more minute apertures, and which is of essential importance in the solution of the food. In some instances, as in the American ostrich (fig. 2), they are few in number, and occupy only a small part of the posterior wall of the oesophagus.

The gizzard or proper stomach of birds may be considered as a horny mucous membrane, somewhat cartilaginous, continuous with that of the oesophagus, and covered by two strong thick muscles, the fibres of which converge to a point. (Plate XXXVI. fig. 1.) In the carnivorous and piscivorous genera of birds, especially those in which the crop is wanting, the gizzard loses its muscular character, and is converted into a membranous pouch.

The stomach of Reptiles does not present those dilatations observed in Birds; and when it changes its diameter or capacity, it is only progressively and insensibly. Its general diameter, nevertheless, is proportionally larger than in the two classes already noticed. Most generally without cul de sac, its shape is spheroidal, more or less oblong; its membranous walls are thin and transparent; its muscular layer almost imperceptible; the cellular identified with the mucous tissue; the situation of the cardia indeterminate; and the pylorus, without valve, is distinguished by a simple tapering contraction of the gastric walls, and the appearance of the structure proper to the intestines.

In this class of animals, further, digestion appears to be less regulated by fixed principles than in the other two. It is evidently not confined exclusively to the stomach. The oesophagus of the turtle is provided with numerous large, firm, pointed processes, which in all probability contribute to the mechanical division of the food, so much the more requisite as the Chelonian Reptiles are toothless. Except in the crocodile, the Saurian Reptiles are destitute of large arch or proper cardiac cavity. In the Ophidian or Serpentine Reptiles the stomach has the figure merely of a dilated sac between the oesophagus and intestines, and presents no curvature. It is probably in connection with this modification of structure that we find animals remain for days in the oesophagus of serpents; and this tube appears to be to a certain extent capable of digesting aliment as much as the stomach. The best mark of distinction in such circumstances is the cessation of epidermis.

In no class of animals does the stomach vary more in shape, structure, and situation, than in Fishes; and perhaps the general character of the alimentary canal in this class is most justly given by representing it as deviating from those attributes of regularity which we find in the higher classes. While in the Mammalia and Birds it is always distinguished by its spheroidal or pyriform enlargement between two tapering extremities, and by being much more dilated than any other part of the alimentary canal, in the Reptile class it begins to part with this character; and it loses it altogether in the Fishes. In most of the finny tribes it is often not more capacious than the oesophagus; and it is distinguished from this tube only by the villous character of its internal membrane. In general, also, the situation of this pyriform dilated sac is transversely across the body in the Mammiferous class. In the feathered tribes this character also is slightly set aside, and partly from the alteration in shape, partly from that of position, the stomach occupies less of the transverse diameter than of the longitudinal extent of the body. Among the Reptiles this character, though still retained in the Chelonian, and even in the Saurian, is gradually enfeebled in the Ophidian; and in the Fishes it may be said to be entirely obliterated, since the organ occupies much more longitudinal extent than transverse width of the body.

The first character of the alimentary tube of fishes is the width or capacity combined with shortness of the oesophagus. The latter character is manifestly associated with the absence of lungs and consequent want of chest; so that between the throat and abdominal cavity, the interval, which corresponds only to the space occupied by the heart, is extremely abridged. The oesophagus consists, as in the other classes, of a mucous membrane surrounded by a muscular tunic; but the mucous membrane is distinguished by the firmness and whiteness of its corion, which in some genera approaches to the consistence of horn or cartilage, and by the presence of conical papillae, sometimes of great hardness, and which appear to Compara- act mechanically on the food. It is almost superfluous to notice the facility which the large capacity of this tube affords fishes for swallowing their prey. Most of them are voracious in the extreme; and it is not uncommon to find the stomach and oesophagus crammed to the throat.

The figure and position of the stomach of Fishes are so variable, that it is difficult to give a character of general application. Though in many genera, especially of the Jugulares, it consists of a cylindrical sac with a slight dilatation immediately below the cardia, in others it is oblong ovoidal, as the ray and shark tribe; and in others, as the sole, dory, and flat fishes generally, it is orbicular. In the sturgeon it consists of a cylindrical tube incurved twice on itself. In none is there more than one cul de sac, the depth of which varies as the part corresponding to the pylorus is more or less remote from the fundus. When the limits of the stomach are indistinct, the situation of the cardia is equally so. In the lamprey (petromyzon) and pen-fish (synognathus pelagicus) the whole tube is of a uniform size from the mouth to the anus; and much the same may be said of the carp genus. The genera in which it forms a distinct dilatation or cul de sac are chiefly the following; the eel (muraena anguilla), conger (m. conger), the bullhead genus (codus), the scorpaena horrida, labrus genus, perch, cuckoo gurnard, mackerel, herring, salmon, morayenus genus, mullet, and silurus Bagre. In the anableps the dilatation disappears; and in the chetodon ciliaris and some others it is a large sac incurved in an arch-like bend.

The intestinal canal in most of the Mammalia is very similar to that of man; and the chief differences of different orders and genera are found in the difference of longitudinal extent either of the whole intestinal tube or the comparative lengths of its several parts.

From the time of Grew to that of Cuvier, and most modern anatomists, it has been a point of some importance to determine the length of the intestinal tube in relation to that of the body. This comparative length, which is greatest in the Mammalia, diminishes successively in the Birds, Reptiles, and Fishes. It has been occasionally stated by different anatomists, that the intestinal tube is longer, easter paribus, in granivorous than in carnivorous animals, and conversely. When we come, however, to compare the different lengths of this tube in the several tribes, we find that this statement demands modification. In the ape family its length varies from 5 to 8 times that of the body; in several of the lemur tribe from 4 to 6 times, the smaller length being in this case compensated by the size of the caecum; and in others of the lemur tribe, e.g. the lori, the intestine is only three times the length of the body. Among the Chiroptera there are two examples of very great contrast in this respect. While the intestine of the noctula or great bat (vespertilio noctula, Lin.) is the shortest of all the Mammalia, and scarcely does more than exceed the length of the animal's body, that of the roussette (pteropus) or East India bat, which lives chiefly on vegetable matter, is at least 7 times longer than its body. A similar instance of the meeting of extremes is found in the Marsupial order, in which the marmoset and cavapolin have intestines only 2½ times longer than the body, while that of the phalanger is more than 11 times longer. In the plantigrade or ursine family, which occasionally live on vegetable matters, the proportional length approaches to that of the ape.

In the carnivorous animals the intestine, though generally short, varies from 3 times to 8 times the length of the body. The former is the proportion in the lion, wild cat, ocelot, cougar, and weasel; and the latter in the hyena. Some of them also vary among themselves. Thus the intestine of the wild cat is greatly less than that of the domestic animal. The proportion is very great among the Rodentia, in several of which it is 8, 10, 12, or 16 times longer, as in the agouti, than the body of the animal. Among the murine tribe, however, it undergoes a diminution. Among the Edentata, again, especially the sloth tribe, it diminishes very much, being only about 3½ times longer than the body in the Ai and Unau. This brevity is so much the more extraordinary that these animals are void of caecum, and live on vegetable matters; but, in all probability, the duplicature of the gastric cavities in some degree compensates this deficiency.

The intestinal tube attains its greatest proportional length in the Ruminant animals, being at least 11 times longer than the body, as in the goat, and 28 times longer in the ram. This immense length is supposed to compensate the absence of dilatation in the large intestines, and the small size of the caecum. In the Soltungula, again, which are remarkable for the large size of the caecum, the length of the intestine diminishes much, being 8 times longer than the body in the zebra, 9 times in the ass, and 10 times in the horse.

Lastly, it is a singular circumstance, that in different species of the same genus the comparative length varies much. We have already noticed the difference between the length of the intestine in the wild and in the domestic cat. The wild and tame boar is a similar instance of the same, the intestine being only 9 times longer than the body in the former, and so much as 13½ times in the latter. It is possible that such differences may depend on the different habits of the animal in his wild and domestic condition. This explanation, however, is totally inadequate to account for the difference in the comparative length of the intestinal tube in the Asiatic and African elephant, being 10 times longer than the body in the former species, and only 7 times in the latter. The same may be observed of two animals very closely allied, if not of the same genus, the echidna and ornithorhyncus. The intestine of the former animal is 7 times longer than his body, while that of the latter is only 5 times.

In Birds generally the intestine is shortest among those genera which prey on animals and fish; it varies from twice to five times the length of the body. In the gallinaceous and passerine birds, which live on grains, it is always longer and more capacious than in those which live on animal substances. In the cassowary, which is granivorous with a short intestine, the intestine is divided by contractions into distinct pouches, to compensate for the brevity of the tube. It must be remarked, nevertheless, that in several birds which prey on fishes, the intestinal tube is proportionally longer than in those which feed only on grain; and the proportional length is not diminished in birds living indiscriminately on animal and vegetable aliment.

The intestinal tube of the Reptiles is still shorter than that of Birds, and often it does not exceed twice the length of the body. It is longest in the Chelonia, and shortest in the Ranine and Serpent tribe. In the tadpole, however, a singular peculiarity is observed. The intestinal tube of the tadpole of a frog is nearly ten times longer than the space between the muzzle and the vent (anus); whereas, after the animal has become a frog, the intestine is only twice as long as this space.

In the class of Fishes the intestinal tube is still shorter and more direct in its course to the vent or outlet. In a few which live chiefly on marine vegetables, for instance some of the chetodon genus, it is about six times longer than the body of the animal; and in a few of the carp genus (viz. cyprinus cepatus) it amounts to ten or twelve times longer than the body. In others, however, of the same genus, for instance the cyprinus murra, it is scarcely as long again, showing here once more an instance of the conjunction of extremes not easily explained. In most vertebrated animals the intestinal tube may be distinguished by natural marks into two divisions, one extending between the pyloric end of the stomach to a part of the tube, where it becomes wider and more capacious; the other from this to the vent or outlet. In some instances, however, this distinction is very obscurely and imperfectly marked. In the Mammalia, in which the distinction is observed, it is indicated by one or more appendages, which, if large, are denominated cæcæ, and if slender and long, are termed vermiciform processes. Man, the orang, and the wombat (phascolomys), are the only animals which are possessed at once of cæcum and vermiciform appendage. In the other genera of the ape tribe, in the maki of the lemur, in the colugo among the Chiroptera, the ichneumon, many of the carnivorous tribe, the opossum and kangaroo, the Rodentia except the dormouse, the Cape ant-eater, the Pachydermata except the hyrax, the Ruminants, Solidungula, and Amphibia, there is only a cæcum without vermiciform process. The cæcum is wanting in the sloths, the bat tribe, the Ursine except the ichneumon, the marten, pine-marten, weasel, &c., the dormouse, and all the Cetaceous animals.

The presence of cæcum or vermiciform process, however, is not necessary to distinguish the canal into two portions. The inner or mucous surface of the ileum is always villous and uniform; and the whole intestine, except its superior or pyloric portion, is convoluted in proportion to its length, and moves about freely in the abdominal cavity; whereas the colon is more or less fixed at different points, it is shorter and more capacious, and its inner membrane is merely mucous without long villi. A mark equally general is the semilunar duplicature of mucous membrane placed between the ileum and colon, and named the ileocolic valve. In the sloth and armadillo tribes, which want cæcum and vermiciform process, this and the slight difference of diameter are the only marks of distinction between the ileum and colon. In all the other Mammalia which are destitute of cæcum the whole tube is of the same calibre, occasionally diminished towards the vent; and the division into ileum and colon is no longer cognizable.

In all the Mammalia with one cæcum, it appears in the form of a production from the large intestine beyond the part at which it receives the ileum; and though variable in its diameter and structure, it bears a general resemblance to the colon in these respects. In herbivorous animals, and even in some that are omnivorous, as the ape and lemur tribes, it is generally large and puckered by tendinous bands. To this, however, an exception is observed in the Ruminants, in which the cæcum is moderate in size and unpuckered. It is small and unpuckered in the kangaroo-rat and wombat; while, conversely, in the colugo and brown phalanger, which are believed to be chiefly zoophagous, it is very large and puckered.

In the zoophagous animals generally both the colon and cæcum are of small calibre, little different from that of the ileum; and both the colon and cæcum are destitute of cells or compartments. In herbivorous and several omnivorous animals, on the contrary, the inner surface of the colon is divided by longitudinal and transverse bands into a number of cells or compartments. From this rule, however, there is an exception in the wombat, kangaroo, and the Ruminants. In the Rodentia the colon is cellular at its commencement only.

In birds the canal is provided with two cæca, one on each side, not far from the vent. In the omnivorous and granivorous these cæca are generally long and capacious. While they are very large in the nocturnal predatory birds, they are either obliterated or wanting in the diurnal predatory birds, in the green woodpecker, the lark, and the cormorant. In the heron, bustard, and grebe, there is a single small one; in the cassowary two very slender; and in the merganser, diver, &c., they are short and thick.

In all birds the short bowel between the insertion of the cæca and the cloaca is a little wider and more capacious than those between the pylorus and the cæca; and this is the only circumstance which indicates in this class the distinction of the tube into ileum and colon.

In the reptiles the intestinal tube is generally void of cæca or appendage; and the only distinction consists in the one part of the tube, which is long and slender, being joined to another which is short and thick, and in the presence of a semilunar membranous fold at the point of insertion. In the iguana alone has a genuine cæcum been observed.

The distinction into small and large intestine, or ileum and colon, is still less obviously observed in the class of fishes. It sometimes happens that the difference of capacity is inverted, and that the calibre of the portion which terminates at the vent is actually smaller than that of the part connected with the stomach. This arrangement is observed in the ray, shark, sturgeon, and even the bichir; in the synaptus, trunk-fish, and balista. In other instances the diameter is the same throughout; and the only distinction is derived from the anatomical characters of the inner membrane. In the lamprey, sea-devil, rough star-gazer, radiated sole, holocentrus sago, carp tribe, morayrus, and mullet, it is impossible to distinguish the intestine into large and small.

Fishes resemble Reptiles in being destitute of cæcum Pyloric ap. at the junction of the small and large bowel. In many of pendages them, however, there is attached to the intestine, some- of fishes where below the pylorus, a variable number of small intestines terminating in blind ends, similar in size and structure to the intestine with which they communicate. These tubes, which have been not very happily named pyloric appendages (appendices pylorice), in so far as they are most frequently connected rather with the part of the bowel corresponding to the duodenum, vary in number from 2, 4, 6, or 8, to 80 or 180 in some genera, and even their number is not the same in different species of the same genus. Thus, while there are 6 in the smelt (salmo eperlanus), there are 68 in the s. lacustris, and 70 in the salmon (s. solar). In like manner, though there are 18 in the anchovy (clupea encrasicolus), there are 24 in the herring (c. harengus), and fourscore in the shad (c. alosa). In some, as the cod and pollach, they consist of several large trunks ramified into numerous small ones.

These appendages, however, are wanting in the cartilaginous fishes with free branchiae, in most of those with form of the fixed branchiae, in the Apodes, and in several of the tho-appen-radic and abdominal order. In the sturgeon and some others they are represented by a series of communicating cavities inclosed in the intestinal membrane, which is covered by a cellulo-muscular tunic and peritoneum (Plate XXXVI. fig. 5), and which assumes the external appearance of a pancreas.

Among the cartilaginous fishes the brevity and directness of the intestinal tube is compensated by a peculiar dis-value of position of the intestinal mucous membrane. This consists in part of the membrane projecting like a broad fold or process from the inner surface of the intestine, and winding round from the pylorus to the anal or lower extremity (fig. 7 and 8). This, which is denominated the spiral valve, may be easily understood from these figures, which represent the arrangement as it is observed in the shark. In the sturgeon, in which it is found in the last portion of intestine (fig. 6), its peculiarities have been described by the writer of this article in the Wernerian Transactions, vol. vi.

In all the Mammalia the intestinal tube terminates Rectum, in a distinct bowel denominated the rectum, the mucous membrane of which is continuous with the skin at the This rule can scarcely be said to be violated in the case of the echidna and ornithorhynchus, in which there is an aperture at the lower part for the urine and the semen of the male and the ova of the female. These anomalous and singular animals form a transition to the mode in which the intestinal tube terminates in the three genuine oviparous classes. In Birds, Reptiles, and most of the cartilaginous Fishes, the intestinal tube terminates in an outlet common to it with the urinary organs, denominated generally the cloaca. In the sturgeon, however, it has been shown, in the paper already mentioned, that there is a distinct urinary outlet; and that consequently this animal cannot be said to have a cloaca. In the greater part of fishes, while there is one vent for the excrement, there is another common one for the urine, the ova, and the spawn.

On the subject of the liver, spleen, and pancreas, it is impossible to enter with any interest in this sketch.

**CHAP. II. SECT. I.—THE HEMATOPHIC ORGANS.**

The Mammalia and Birds agree in having a heart consisting of two pairs of chambers, a venous auricle and ventricle, and an arterial auricle and ventricle. The Eustachian valve is often wanting in the Mammalia. It is wanting, for instance, in the lion, bear, and porcupine; while it is broad and muscular in the seal, and assumes a spiral direction along the upper walls of the right auricular sinus in the elephant.

It was at one time imagined that the aquatic Mammalia were distinguished from the terrestrial by the foramen ovale being open and forming a communication between the two auricles. This, however, is a mistake, at least in the adult animal; for neither in the otter, the seal, nor the porpoise or dolphin, did Cuvier find this aperture previous; and it may be inferred, that when it is open, it is an abnormal remain of the fetal structure. In the ornithorhynchus, also, according to Sir Everard Home, it is impervious. In the porcupine and elephant, in which there are two anterior vene cara, the blood of the left anterior cara, which opens in the sinus near the aurico-ventricular aperture, is conveyed directly into the right ventricle.

The reptile heart, the first in the cold-blooded division, varies somewhat in the several tribes. In the first three, the Cheloniad, Saurial, and Ophidian, it consists of two auricles and one ventricle, divided in some instances into communicating chambers. In the Batrachoid family, on the contrary, it always consists of one auricle and one ventricle, the interior of which is unilocular or undivided. In several of the Turtle tribe, among the first family, the ventricle consists of a pulmonary chamber, in which the blood is more particularly directed to the pulmonary artery, and a general or aortic chamber, which is above, and from which the blood is conveyed into the aorta. In the crocodile the ventricle is divided into three chambers, communicating by several apertures. One is inferior and to the right, and communicates with the right auricle by a large aperture provided with two valves. On the left, and before, is the second chamber, receiving the orifice of the left descending aorta. Behind is an aperture leading into the smallest chamber of the three, situate at the middle of the base of the heart, and receiving the common trunk of the pulmonary arteries. The left chamber is above. In the Ophidian or Serpentine family the ventricle is divided into two chambers, a superior and inferior, separated by an imperfect partition, which allows the two to communicate.

The heart of the finny tribes is as simple as that of the Ranine reptiles, which indeed constitutes the preparatory step in the descending scale of organic forms. It consists, as in these animals, of two chambers only, an auricle and ventricle. The former receives the blood from the body at large, and transmits it to the ventricle, which is almost unilocular. From this a single vessel conveys it, not to the body at large, but to the gills, from which it is again collected by several branchial veins.

Of the blood-vessels of the four vertebrated classes it is superfluous to speak in any detail.

The most remarkable circumstances are the minute subdivisions which in some classes the arteries undergo previous to final distribution. In the Ruminants, and several of the Pachydermata, the branches of the carotid artery, instead of uniting by the communicating vessels, are subdivided into a great number of minute vessels, which form round the pituitary gland a communicating plexus, denominated by the ancients Rete mirabile.

In the slow lemur (lemur tardigradus) Sir A. Carlisle found the subclavian artery, after entering the axilla, divide into 23 arterial cylinders of equal size, and the iliac on the brim of the pelvis into at least 20 equal-sized tubes, which in both cases surrounded the principal artery, reduced to a small vessel, and, proceeding along the extremity, were distributed chiefly to the muscles. (Phil. Trans. 1800.) A similar arrangement, carried to a still greater extent, was found in the Ai or three-toed sloth, in which the axillary and iliac arteries were divided into about 60 or 65 cylindrical parallel tubes. In the slender lemur (Lemur loris) these vessels are subdivided into 4 or 5 only.

In fishes in which the unilocular ventricle sends its blood to the gills only, the heart is pulmonary, and the arterial system is destitute of central impulsive organ. In the sturgeon, which is one of the best examples of the distribution of the arterial system in the finny tribes, the blood, which is distributed in the branchiae by the large artery, is collected in numerous vessels, which may be regarded as analogous to the pulmonary veins of the warm-blooded classes, but which have thick parietes like arteries; and these uniting, form a large vessel, which is lodged in a cartilaginous canal formed by the continuous bodies of the vertebrae. This vessel is further void of compressive or elastic tunics, and the blood moves through it as through an immovable and inelastic tube. From its sides, however, a series of arterial vessels issue, which forthwith assume the usual characters of arterial tubes. In many other fishes the parietes of the large artery adhere in part to the semi-osseous canal in which it is lodged.

**SECT. II.—THE ORGANS OF AERATING CIRCULATION.**

The lungs of the Mammalia are in all essential points perfectly similar to those of the human subject.

The lungs of Birds differ chiefly in not presenting distinct lobules, in having the air-vessels larger and more distinct, in the branchial tubes not becoming quite so small, and in terminating not alone in the pulmonic vesicles, but in perforated parts of the surface of the lungs, which lead into large air-sacs, communicating with all parts of the body, and forming an accessory lung. In the ostrich, which may be taken as a general example, there are four of these cells or aerolabous sacs. The first, which is anterior, extends from the apex of the chest to the iliac bones, between the first ribs and heart above, and between the lower ribs and a cell which surrounds the intestines. It is divided into four chambers, the first two communicating with the lungs by large apertures, while the fourth opens in the iliac bones. Behind this large sac are two small ones, between the iliac bones and the peritoneal sac. Before it is another small one occupying the lateral regions of the apex of the chest, and communicating with sacs in the axilae and neck. Besides these, the stomach, liver, heart, and intestines are surrounded by sacs. All of these communicate by saccular processes with the cavities of the bones. By this peculiar arrangement Birds possess the greatest extent of respiratory surface of all classes of animals. The lungs of Reptiles are distinguished by consisting of large sacs, subdivided by membranous partitions into polygonal cells, which again are subdivided by smaller slips into smaller cells. In these cells the bronchial tubes are not ramified, but divide abruptly in them at the surface of the lung. Some idea of this arrangement may be obtained from the lung of the ordinary land-tortoise (Testudo Graeca, Plate XXXVII. fig. 1). The sacs or large cells are smaller and more numerous in the turtle (fig. 2); but the general disposition is much the same.

The young of the Batrachoid family, and several of the water-lizard tribe, are provided with fimbriated or ciliated processes attached to the neck, and which are in all respects similar to the gills of fishes. These gills disappear as the animal grows; and when it assumes the true ranine or reptile character, vesicular lungs like those of other reptiles, and which had continued in a hitherto latent and rudimental state, are developed, and the animal breathes as others of the same tribe.

A peculiar form of respiratory organ is found in the lamprey or seven eyes, and the two species of hag-fish, (Myxine, Lin.; Gastrobranchus, Bl.; and Gastrobranchus Dumeril). The former has on each side seven apertures leading into cylindrical tubes, in which the branchiae are contained. (Plate XXXVII. fig. 3.) In the two species of hag these tubes are dilated into ovoidal cavities, in which the water is received, and on the membrane of which the branchial vessels are distributed. In this respect, therefore, the hag-fish approaches to the mode of respiration among the cephalopodous Mollusca, in which the branchiae are inclosed in a cavity. Lastly, in the Aphrodite aculeata, which may be taken as an example of the respiration of worms, there is a series of tubes like tracheae and bronchi, proceeding from the surface to the interior, and in which the water containing the air requisite for respiration is received. (Fig. 6.)

**SECT. III.—SECRETORY ORGANS.**

Under this head ought to be described the urinary organs of the four vertebrated classes. Those of the Mammalia agree in consisting of kidneys more or less lobulated, ureters or excretory tubes, a reservoir or urinary bladder, and a urethra opening on the same mucous surface with the organs of generation. In the three oviparous classes considerable changes are made. Though in Birds and Reptiles the glandular organs denominated kidneys are left in the shape of aggregated glands with the two excretory tubes, the bladder is withdrawn, and the ureters open in the cloaca. The only apparent exceptions are the ostrich and cassowary, in which the cloaca is so organized that it may serve as a bladder or temporary receptacle of the urinary secretion. In the Reptiles the presence of this organ is variable, being found in the Cheloniad and Batrachoid; and the iguana, tupaianbis, chameleon, stellio, and dragon, among the Saurial tribe; but wanting in the crocodile, lizard, agami, gecko, and the whole Ophidial tribe. In Fishes it is not less variable. While the ray and shark tribe are destitute of bladder, and the ureters terminate in a cloaca, this receptacle exists in the sea-devil, lump-fish, globe-fish, and others of the cartilaginous division.

A peculiar secreting organ, deserving notice, is the poison gland of the poisonous serpents. It is a glandular body situate on each side above the upper jaw, behind and below the eyes, with a considerable cavity, which opens into a long excretory tube, lying along the outer surface of the upper jaw, and opening in the tubular tooth, represented at fig. 17 and 18; and which is movable in an articulation, and may be erected, as in fig. 18, or depressed, as in 16, at the will of the animal. The poisonous serpents are therefore distinguished from the innocuous by the presence of the erectile movable tubular fangs. Fig. 15 is the head of Comparative Anatomy.

**PART III.—REPRODUCTIVE ORGANS.**

Under this head we mention only the nipple-bag (mamillium mamillare), or secondary uterus of the Marsupial animals (Plate XXXVII. fig. 7); the nipples (fig. 8); and the manner in which the fetal animal, in a very imperfect and embryal form, becomes attached by the mouth to the nipples (fig. 10). The Marsupium, therefore, ought to be regarded, not as a mere pouch in which the young may take refuge after they are grown, but as a subsidiary uterus, combining the character of the Mammae of the other orders.

The Mammalia are peculiar in possessing a uterus. In the other classes this organ is withdrawn, and the ovary (fig. 11) and oviduct alone are left. In the ovo-viviparous animals, as the ovo-viviparous shark, the oviduct (fig. 12) resembles that of the common fowl. In the lower classes the ova are hatched out of the body entirely.

In the space assigned to this article, it was impossible to treat fully of a subject so extensive as the structure of the animal world; and while the author has arranged its divisions in such a manner as to show in what order it may be most easily and advantageously studied, he has introduced only those topics which are most indispensable, and most require illustration. For more complete details, therefore, he refers the reader to the following works.

1. *Leçons d'Anatomie Comparée* de G. Cuvier, Membre de l'Institut National, &c.; recueillis et publiées sous ses yeux par C. Duméril, chef des Travaux Anatomiques, &c. Cinquantes. Paris, tome i. 1799.—tome v. 1805. 2. Blumenbach's *Manual of Comparative Anatomy*; with additional Notes by William Lawrence, Esq. F.R.S. Second edition, revised and augmented by William Coulson Lond. 1827, 8vo. The notes are derived chiefly from the work of Cuvier and the papers of Sir E. Home in the *Philosophical Transactions*. 3. Gore's Translation of *Cuvier's Introduction to the Comparative Anatomy of Animals*. Lond. 1827, 2 vols. 8vo. The arrangement of this work, in which the author examines the forms of organs as they ascend, from the lowest to the highest classes, diminishes its general interest. 4. *Lectures on Comparative Anatomy*, in which are explained the *Preparations in the Hunterian Museum*. By Sir Everard Home, Bart. Lond. 1823, 6 vols. 4to. This work consists of the papers read by the author at the Royal Society, and published in their Transactions. Though entitled, therefore, *Lectures on Comparative Anatomy*, it embraces a much more extensive field, and contains a great number of physiological and pathological papers. This renders it at once rather desultory and prolix. It contains, nevertheless, a great number of facts illustrative of peculiarities of structure in the animal world; and it is particularly valuable by the number of engravings with which it is embellished. It can scarcely be said to possess any arrangement whatever.

5. *Recherches sur les Ossements Fossiles, où l'on rétablit les caractères de plusieurs animaux dont les Révolutions du Globe ont détruit les espèces*. Par M. le Bar. G. Cuvier, &c. Nouvelle édition. Tome i. 1822, Osteology of the Elephant, Hippopotamus; tome ii. partie i. 1822, Osteology of the Rhinoceros, Horse, Hog, Damian, and Tapir; tome iv. 1823, Osteology of the Deer and Ox, the Bear, Hyena, Lion, Glutton, Wolf, and Dog; tome v. partie i. 1823, Osteology of the Reptiles, the Ichthyosaurus and the Plesiosaurus; partie ii. 1823, Rodentia, Edentata, Monotrema, Amphibia, and Cetacea. Paris, 1824. These papers contain much accurate osteological description.