The art of dissecting, or artificially separating and taking to pieces, the different parts of the human body, in order to an exact discovery of their situation, structure, and economy.—The word is Greek, ἀνατομή; derived from ἀνατέω, to dissect, or separate by cutting.

INTRODUCTION.

§. I. History of Anatomy.

This art seems to have been very ancient; though, for a long time, known only in an imperfect manner. —It probably first took its origin from the custom of sacrificing animals to the Deity; and as some parts only were appointed for sacrifice, and others for the use of the priests, those who were concerned in perform- ing this religious ceremony behaved to be as much masters of anatomy as to distinguish the one part from the other.

It was indeed impossible that any number of animals could be slaughtered, either for sacrifice or food, but those who performed the butcher's part behoved to be acquainted with the general situation of the viscera; and accordingly we find, by the directions given to the Jews concerning their sacrifices, that these things were well known in the time of Moses. It is also prob- able, that as for a long time every man was butcher for himself, the slight knowledge of anatomy which butchers can acquire was pretty general in every na- tion.

By viewing the bodies of slaughtered animals, how- ever, only a knowledge of Comparative Anatomy, as it is called, could be acquired. The knowledge of the internal parts of the human body might possibly origi- nate from the barbarous custom of human sacrifices on certain occasions. This made it necessary for the priests to acquire some knowledge of the internal structure of the human body, and they would not want opportunities from those slain in battle, or torn by wild beasts; accordingly we find in Homer's Iliad some degree of anatomical knowledge displayed, by his accurate details of some of the viscera wounded by weapons passing from certain external parts of the body.

The first hints we have of anatomy being adopted as a science or part of natural philosophy, are, That Thales of Miletum, and Pythagoras, about 700 years before Christ, made it a part of their studies.—A hundred years after this, Empedocles, in a little fragment preserved by Galen, discovers considerable anatomical knowledge, and is thought to have prevented Fallopius in the discovery of the cochlea and tube of the ear.

Alcmaeon of Crotona, a disciple of Pythagoras, is thought to have been the first who dissected animals with a view to learn their internal structure. This was done by Democrates of Alberda, with a philosophical, and by Hippocrates with a medical view, about 500 years before Christ.—Diodes the Caryfithian is said to have been the first who wrote the method and order of dissecting the parts of animals; but his works are now lost.—The next who had any reputation in anatomy was Praxagoras the Coan; of whom all we know is, that he distinguished the veins from the arteries, and believed that the latter became nerves as they grew smaller.

It is probable that the Greeks learned their knowledge of the arts from the eastern nations, as all the Grecian worthies esteemed it one of the best parts of their education to travel into those parts.—Egypt seems to have been originally a great seminary of learning. Under the first Ptolemies, Soter and Philadelphus, a school was erected at Alexandria, where, among other sciences, anatomy was publicly taught; the kings were sometimes present at the dissections of human bodies, and brutes were furnished by their command. Herophilus and Eratistratus were the successors of two of the first masters in this school, and each of them is said to have dissected several hundred bodies, from which probably the report arose of their having dissected living men. Eratistratus described the lacteal vessels of a kid, and the true origin and use of the nerves, in which last discovery Herophilus of Carthage has shared with him. By some he has been supposed to have known the circulation of the blood; and we are certain that he accounted for digestion by the mechanical action and pressure of the stomach, as some moderns have done. The works of these great men are lost, and all we know of them is from little scraps of improvements interspersed in the works of Galen.

Among the Romans, though it is probable they had physicians and surgeons from the foundation of the city, yet we have no account of any of these applying themselves to anatomy for a very long time. Archagathus was the first Greek physician established in Rome, and he was banished the city on account of the severity of his operations.—Aclepiades, who flourished in Rome 101 years after Archagathus, in the time of Pompey, attained such a high reputation as to be ranked in the same class with Hippocrates. He seemed to have some notion of the air in respiration acting by its weight; and in accounting for digestion, he supposed the food to be no farther changed than by a commination into extremely small parts, which being distributed to the several parts of the body, is assimilated to the nature of each. One Cassius, commonly thought to be a disciple of Aclepiades, accounted for the right side of the body becoming paralytic on hurting the left side of the brain, in the same manner as has been done by the moderns, viz. from the crossing of the nerves from the right to the left side of the brain.

From the time of Aclepiades to the second century, physicians seem to have been greatly encouraged at Rome; and in the writings of Celsus, Rufus, Pliny, Celsus Aurelianus, and Aretaeus, we find several anatomical observations, but mostly very superficial and inaccurate. Towards the end of the second century lived Claudius Galenus Pergamus, whose name is so well known in the medical world. He applied himself particularly to the study of anatomy, and did more in that way than all that went before him. He seems, however, to have been at a great loss for human subjects to operate upon; and therefore his descriptions of the parts are mostly taken from brute animals. His works contain the fullest history of anatomists, and the most complete system of the science, to be met with anywhere before him, or for several centuries after; so that a number of passages in them were reckoned absolutely unintelligible for many ages, until explained by the discoveries of succeeding anatomists.

About the end of the fourth century, Nemesius bishop of Emilia wrote a treatise on the nature of man, in which it is said were contained two celebrated modern discoveries; the one, the uses of the bile, boasted of by Sylvius de la Boe; and the other, the circulation of the blood. This last, however, is proved by Dr Friend, in his History of Physic, p. 229. to be falsely ascribed to this author.

The Roman empire beginning now to be oppressed by the barbarians, and sunk in gross superstition, learning of all kinds decreased; and when the empire was totally overwhelmed by those barbarous nations, every appearance of learning was almost extinguished in Europe. The only remains of it were among the Arabians in Spain and in Asia. They applied themselves chiefly to the study of physic; but as the Mahometan law, like that of the Jews, forbade its subjects to touch dead bodies, anatomy could be but little improved by them. Avicenna, however, applied himself to read and understand the works of Galen. By dissection, he found out what is commonly ascribed to Fallopius, namely, the muscles attollens palpebram superiorem.

By the intercourse of the Europeans next to Spain with the Arabians, learning began to be again introduced; and in the eleventh century, the school of Salerno in Sicily made a considerable figure in medicine. The gross ignorance and superstition of those days, however, prevented for a long time any improvements, and nothing was taught for two centuries afterwards but to understand the Arabian doctors. Anatomical improvements were particularly retarded by its being imagined a crime to dissect a human body; and this opinion prevailed till the 16th century. The emperor Charles V. ordered a consultation to be held by the divines of Salamanca, in order to determine whether or not it was lawful in point of conscience to dissect a dead body. In Muscovy, till very lately, both anatomy, and the use of skeletons were forbidden, the first as inhuman, and and the latter as subservient to witchcraft.

Mundinus was the first European author who joined directions to the authority of Galen and the Arabs. He flourished in the beginning of the 14th century, and his system was in such high reputation as to be the only one taught in the schools for a good number of years. In the university of Padua particularly, the professors were tied down by an express order of the academy to teach this book and no other.

In the beginning of the 15th century, learning revived considerably in Europe, and particularly physic, by means of copies of the Greek authors brought from the back of Constantinople; after which the number of anatomists and anatomical books increased to a prodigious degree.—The Europeans becoming thus possessed of the ancient Greek fathers of medicine, were for a long time so much occupied in correcting the copies they could obtain, studying the meaning, and commenting upon them, that they attempted nothing of their own, especially in anatomy.

Towards the end of this century, Jacobus Berengarius Carpus, became the reformer of anatomy and surgery at Bologna in Italy. He says that he had dissected above a hundred dead bodies; which procured him the same character that had formerly been given to Herophilus and Erasistratus, namely, that of dissecting living men.—He published two anatomical works; the one intitled *Ifigaeae*; and the other, commentaries on Mundinus, in which he corrected some erroneous descriptions; and added several discoveries of his own.

For some time the study of anatomy seems to have been peculiar to Italy, and several treatises were published on this subject by the Italians before any thing of a similar kind was produced in any other nation; but about the year 1536, Johannes Guinterius of Anderson, who had taught anatomy for some years at Paris, published his Anatomical Institutions. He was the first anatomist who gave a full and exact description of the muscles; he affirmed, that the muscles which surround the neck of the bladder consisted of transverse fibres; that they had several functions, such as shutting the bladder, and, after the emission of the urine, evacuating what is left in the passage.

In 1543, Andreas Vesalius of Bruges published his anatomy; which was of the utmost service, not only by the many important discoveries he made, but by his daring to correct Hippocrates, Galen, and the Arabians; which paved the way for others to rid themselves of the slavery to these authors, which universal custom had imposed upon them. His descriptions are minute, especially of the bones and muscles; in which he not only outdid all that went before him, but is scarce to be equalled by any modern author. His figures were also esteemed master-pieces of painting; though they would probably have been more serviceable to young anatomists, had they been represented in a flaccid state, as they are by Eustachius, and as they are to be seen in a dead body, than when represented in a strong state of action. He was the first anatomist that professed for a salary.

The criticisms on Galen and the ancients published by Vesalius when only 28 years of age, could not fail of procuring him a number of enemies; which, however, increased, instead of diminishing, his reputation. Among the rest, Jacobus Sylvius of Amiens who had been Vesalius's instructor, endeavoured to decry him; and besides thundering against him in his colleges, he wrote a scurrilous treatise against Vesalius, and in defense of Galen, which he entitled *Calumniatorum Vesalii repulsos*. Besides this he published several other anatomical treatises. He has been particularly serviceable by imposing names on the muscles, most of which are retained to this day. Formerly they were distinguished by numbers, which were differently applied by almost every author.

In 1561, Gabriel Fallopius, professor of anatomy at Padua, published a treatise of anatomy under the title of *Observationes Anatomicae*. This was designed as a supplement to Vesalius; many of whose descriptions he corrects, though he always makes mention of him in an honourable manner. These criticisms, however, were not well relished by Vesalius, though he was obliged to own himself handsomely dealt by. He published an answer, under the title of *Observationum Fallopiae Examen*. Fallopius made many great discoveries, and his book is well worth the perusal of every anatomist.

In 1563, Bartholomaeus Eustachius published his *Opuscula Anatomica* at Venice which have ever since been justly admired for the exactness of the descriptions, and the discoveries contained in them. He published afterwards some other pieces, in which there is little of anatomy; but never published the great work he had promised, which was to be adorned with copper-plates representing all the parts of the human body. These plates, after lying buried in an old cabinet for upwards of 150 years, were at last discovered, and published, in the year 1714, by Lancisi the pope's physician; who added a short explication text, because Eustachius's own writing could not be found.

From this time to the year 1628, though the number of anatomical authors was very much increased, there seems to have been no remarkable discovery made; only Andreas Libavius, tho' not properly an anatomist, ought not to be passed over in silence; because in 1616, from some unknown Paracelsian, he describes a method of transfusing the blood of one animal into another, as a cure for various diseases. But this year (1628) was rendered remarkable by the discovery of the circulation of the blood. This important phenomenon was first observed and demonstrated by Dr William Harvey, who now published his observations. Numbers of opponents immediately appeared; but he had the happiness in his own life to see them all give up their cause, and the whole medical world embrace his doctrine. Some, indeed have endeavoured to rob him of the honour of this important discovery, by pretending that he received it from some contemporary who did not publish it himself, as it would have been reckoned a mortal heresy in some countries. This, however, was never proved.

We now consider anatomical knowledge as approaching to its *ne plus ultra*—So many and so great discoveries were already made, that only the minutiae remained to be discussed by succeeding anatomists. Improvements, however, were still going on. In 1642, Wirtfungs, or Virtfungs, discovered the pancreatic duct; but he did not live to publish any treatise on this discovery, being killed by a bravo at his own door in Padua.—In 1651, or 1652, the lymphatic vessels were discovered by Thomas Bartholin; but this honour was also claimed by Olaus Rubick the Swede, and by the contemporary English writers ascribed to their their countryman Jolivius.

Numberless other discoveries, though of the least important kind, continued to be made.—In 1666, or soon after, Marcello Malpighius began to outdo all his predecessors in the exactness of his descriptions, and the new discoveries he made in the structure of the parts. What gave him so much the advantage over others was his extreme patience, and his methods of preparing the parts, particularly by long maceration. He had also the advantage of microscopes, which before his time were either never used, or in a very inaccurate manner.

At the same time flourished Laurentius Bellinus at Florence, and was the first who introduced mathematical reasoning in physic. In 1662, Simon Pauli published a treatise de Animalis Officis. He had long been admired for the white skeletons he prepared; and at last discovered his method, which was by exposing the bones all winter to the weather.

Johannes Swammerdam of Amsterdam also published some anatomical treatises; but was most remarkable for his knowledge of preserving the parts of bodies entire for many years, by injecting their vessels. He also published a treatise on respiration; wherein he mentioned his having figures of all the parts of the body, as big as the life, cut in copper, which he designed to publish, with a complete system of anatomy. These, however, were never made public by Swammerdam; but, in 1683, Gothofridus Bidloo, professor of anatomy at Leyden, published a work intitled Anatomia Corporis Humani, where all the parts were delineated in very large plates almost as big as the life. Mr Cowper, an English surgeon, bought 300 copies of these figures; and in 1698, published them, with an English text, quite different from Bidloo's Latin one; to which were added letters in Bidloo's figures, and some few figures of Mr Cowper's own. To this work Cowper's name was prefixed, without the least mention of Bidloo, except on purpose to confute him. Bidloo immediately published a very ill-natured pamphlet, called Galilaeus Cowperus citatus coram tribunali; appealing to the royal society, how far Cowper ought to be punished as a plagiarist of the worst kind, and endeavouring to prove him an ignorant deceitful fellow. Cowper answered him in his own style, in a pamphlet called his Vindiciae; endeavouring to prove, either that Bidloo did not understand his own tables, or that they were none of his. This last is most probable; and many people believe that these are the tables promised by Swammerdam, and which Bidloo had got from his widow.

Soon after, Ibrandus Diembroeck, professor of anatomy at Utrecht, began to appear as an author. His work contained very little original; but he was at great pains to collect from others whatever was valuable in their writings, and his system was the common standard among anatomical students for many years.

About the same time, Antonius Lievenshoek of Delft improved considerably on Malpighius's use of microscopes, and supplied what was wanting in Harvey's demonstration of the true circular motion of the blood. He was also the author of an hypothesis concerning the different texture of the blood and serum; but herein he is found to have been mistaken.

Frederic Ruyfus first appeared in print in 1665, and died only in 1730, occasionally publishing anatomical pieces during a course of 65 years. He was for a great many years famous for his method of injecting the most subtile vessels of the body, and for preserving all the parts in their natural colour and texture; both of which arts he is said to have received from Swammerdam, tho' he himself protests solemnly that he found them out by his own industry.

It would be in a manner impossible to give an account of all the authors that have contributed since the beginning of the present century to bring the science of anatomy to that state of perfection in which it now is. The writings of Keil, Douglas, Chedelden, Winiford, &c. are too well known to need description. The latter is generally recommended as a standard for the students of anatomy. It is also superfluous to mention the reputation which Dr Monro at Edinburgh, and Dr Hunter at London, have deservedly acquired, on account of their anatomical knowledge. We shall only take notice of two remarkable improvements, not in the science itself, but in the method of teaching it, that have been made since the commencement of this century. The one is, by Johannes Baptista Bianchi, professor first at Bologna, and afterwards at Turin. He shewed his scholars a body entire, so prepared that he took off one part from another, and finished a complete system of anatomy before he had done: then he artificially joined all the parts together for a new demonstration, so that it could not be known they were ever separated. The other is the art of imitating all the parts of the body in wax; which was brought to the utmost perfection by Georgius des Noves, vel Novellas, professor of anatomy at Bologna; and figures of this kind were publicly shewn at London and Paris.

§ 2. Plan of the following Treatise.

The etymology of the word anatomy, as above given, implies simply dissection; but by this term something more is usually understood.

It is every day made use of to express a knowledge of the human body; and a person who is said to understand anatomy, is supposed to be conversant with the structure and arrangement of the different solid parts of the body.

It is commonly divided into Anatomy, properly so called; and Comparative Anatomy: the first of these is confined solely to the human body; the latter includes all animals, so far as a knowledge of their structure may tend to perfect our ideas of the human body*. *See Comparative anatomy.

The term anatomy may also have another and more extensive signification: it may be employed to express, not only a knowledge of the structure and disposition of the parts, but likewise of their economy and use. Considered in this light, it will seldom fail to excite the curiosity of people of taste, as a branch of philosophy; since, if it is pleasing to be acquainted with the structure of the body, it is certainly more so to discover all the springs which give life and motion to the machine, and to observe the admirable mechanism by which so many different functions are executed.

The human body is composed of solid and fluid parts. We shall not satisfy ourselves with giving a description of the former alone; but we shall likewise speak of the nature of the fluids, and of the reciprocal action of both upon each other. Of the Bones in General.

We begin with the bones, which may be considered as the great support of the body, tending to give it shape and firmness. But before entering into the detail of each particular bone, it will be necessary to describe their composition and connections, and to explain the nature of the different parts which have an immediate relation to them; as the cartilages, ligaments, periosteum, marrow, and synovial glands.

a. The bones are of a firm and hard substance, of a white colour, and perfectly inflexible. They are the most compact and solid parts of the body; and serve for the attachment or support of all the other parts.

b. Three different substances are usually distinguished in them; their exterior or bony part, properly so called; their spongy cells; and their reticular substance. The first of these, is formed of many laminae, or plates, composing a firm, hard, substance. The spongy, or cellular part, is so called, on account of its resemblance to a sponge, from the little cells which compose it. This substance forms almost the whole of the extremities of cylindrical bones. The reticular part is composed of fibres, which cross each other in different directions; this net-work forms the internal surface of those bones which have cavities.

c. The flat bones, as those of the head, are composed only of the laminae and the cellular substance: this last is usually found in the middle of the bone, dividing it into two plates; and is there called diploë.

d. Gagliardi, who pretended to have discovered an infinite number of claviculi, or bony processes, which he describes as traversing the laminae to unite them together, has endeavoured to support this pretended discovery by the analogy of bones to the bark of trees, in which certain woody nails have been remarked: but this opinion has not been confirmed by any certain observation. The resemblance of bones to trees has, with more probability, been observed in their formation. In bones it is by many supposed to arise from layers of the periosteum, which gradually ossify; and it is by the hardening of the albumen (a) in trees that the timber is formed. M. Duhamel, the celebrated academician, has endeavoured to prove the truth of this observation by a great number of facts (u).

e. We usually consider in a bone, its body and its extremities. The ancients distinguished the body or middle part, by the name of diaphysis; and divided the extremities into apophysis and epiphysis; an apophysis, or, as it is more usually termed, process, is an eminence or continuation of the body of the bone; whereas an epiphysis, is a part attached to the bone by means of an intervening cartilage. A great number of epiphyses, which in young subjects appear as separate bones, become, in process of time, so perfectly united to the body of the bone, by the ossification of the cartilage, as not to be distinguished from it in the adult state.

f. Different names are given to the processes of bones, varying according to their figure and size. If a process is large, and of a spherical shape, it is called capitulum, or head; if the head is flattened, it takes the name of condyle. Other processes are called mastoid, styloid, ceratoid, from their resemblance to a breast, a little, or the beak of a crow. Some are styled ridges or spines. All these terms are easily understood; we shall however speak of them again, when we consider the bones which have apophyses.

g. There are, in bones, cavities as well as processes; these cavities either extend quite through the bones, or appear only as depressions. The first of these receive the name of foramina, or holes; and these foramina are sometimes called canals, or conduits, according to their form and extent. Of the cavities which do not penetrate through the bones, some are formed for the articulations; when these are deep, they are called cotyloid; as the great articulating cavity of the thigh, with the os innominatum; glenoid, or scapuloid, when they are superficial; as the cavity of the scapula, which receives the head of the os humeri.

h. Of the depressions which are not useful in articulation, the largest, and those which are not equally surrounded by high brims, are called fossae. On the contrary, cavities with small apertures, are termed sinuses; other depressions take the name of furrows and fissures; when they are long and narrow; and there are some called digital impressions, from their resemblance to the traces of a finger on soft bodies.

a. We shall abridge this article, which is exceedingly diffuse in the generality of anatomical books; and will endeavour to describe it with all the clearness it will allow.

b. The skeleton is composed of a great number of bones, which are all so admirably constructed, and with so much affinity to each other, that the extremity of every bone is perfectly adjusted to the end of the bone with which it is connected; and this connection is termed their articulation.

c. Articulation is divided into moveable and immoveable. The first of these is named diarthrosis, and the second synarthrosis.

When a large head is received into a deep cavity, as is the head of the os femoris, it is called entarthrosis; anthrodes, when a round head is admitted into a superficial cavity; as the articulation of the arm bone, with the scapula. Both these allow motion to all sides.

d. If the articulation permits only flexion and extension, as the articulation of the tibia with the os femoris, it is called ginglymus; which properly signifies the hinge of a door, or window. In this the parts of the bones mutually receive and are received.

Vol. I.

(a) The albumen is the soft, white substance, which in trees is found between the liber, or inner bark, and the wood.

(b) M. Duhamel, with a view to support his system of ossification, fed different animals with madder and their ordinary food, alternately, during a certain time; and constantly observed, in dissecting their bones, distinct layers of red and white, which corresponded with the length of time they had lived on madder, or their usual aliment. The same trials, however, have been since made with the madder in England, and were found not to correspond with Duhamel's account of its effects. The synarthrosis, or immovable articulation of bones, is divided into the fixture and gomphosis. In the fixture, the two bones are mutually indented into each other; and of this, the junction of the parietal bones is an example. When the marks of this articulation were more minute, the ancients gave it the name of harmonia; but this variety of names seems to be useless. Gomphosis, is the fixing one bone into another, as a nail is fixed into a board; and thus the teeth are secured in their sockets. The perfect union or concretion of two bones, is called symphysis; as the lower jaw, which in infancy is composed of two distinct bones; but becomes one in a more advanced age, by the ossification of the uniting cartilage.

f. When bones are thus joined by the means of cartilages, the union is filled symcondyly; if by ligaments, syndesmosis.

a. Cartilages are white, solid, smooth, and elastic substances, between the hardness of bones and ligaments; and are usually placed at the extremities of bones.

b. Many of them ossifying in process of time, a greater number are observed in the fetus, than in the adult state: from the same cause the number of bones is greater in young than in old people; because it sometimes happens that a cartilage placed between two bones ossifies; and the three parts, which were before distinct, are united together. This takes place in the sternum.

c. The great use of the cartilages is in the articulations; where, by their smoothness, they facilitate motions which the bones alone could not execute with so much freedom. They are likewise useful in the formation of the voice, and for the attachment of muscles. The cartilages, as well as the bones, are insensible (c), not because they are destitute of nerves, (being formed, according to M. Duhamel's observations, from the periosteum); but because the closeness of their texture prevents their nerves from receiving, or transmitting any impressions. The soft parts, which become callous or scirrhouss, lose (d) their sensibility from a similar cause.

a. The periosteum is a fine (e) membrane, which covers almost all the bones. This membrane, though of a very thin texture, is composed of a great number of layers, which usually offish one after the other, as the body advances in age.

b. Havers pretended to have discovered, that the periosteum is composed of two sorts of fibres; one of which are placed close to the bone, longitudinally from one end to the other, deriving their origin from the dura mater, which passes out of the cranium in different places; and goes to distribute itself to all the bones in the body. The other order of fibres he supposed to arise from the tendons and muscles. He affirms that they are not longitudinal like the first, but that they follow the same direction as the parts from which they are produced.

c. The periosteum has sanguiferous and lymphatic vessels, and is said to be supplied with nerves (f) from the neighbouring parts: it supports the vessels which go to distribute themselves through the substance of the bones, the periosteum internum, and the marrow.

(c) In the course of this treatise mention is often made of the sensibility or insensibility of different parts, and it will perhaps not be amiss to give the outlines of a system, which cannot but be interesting to all anatomical readers.—Baron Haller was the first who publicly asserted, that living animals, whose cartilages, ligaments, capsules of the joints, tendons or periosteum were cut, burnt or torn, shewed no signs of uneasiness; and that the wounds of all these parts were cured without any bad symptoms.—In his publication on this subject, he allows feeling to the teeth; but not to the other bones; because they are destitute of nerves.—He ventures to deny sensibility to the marrow, not from any experiments of his own on living animals, but because it is a fatty substance without nerves.—He tells us, that when the dura mater was torn or burnt, with oil of vitriol, the animal seemed insensible of the injury; that with the pia mater it was the same; but that the moment the brain itself was wounded, the body of the animal was exceedingly convulsed—he makes the same conclusions from similar experiments on the peritoneum, pleura, and pericardium, and concerning the mediastinum, from its analogy to them as a membrane. He describes the cornea as insensible, because it nerves cannot be demonstrated, and it is often pierced with a needle without pain.—From a variety of interesting experiments, which he has fully related, he concludes, that all these parts are perfectly insensible; that they have been unjustly accused by physicians as the seat of many painful diseases; and that their insensibility argues their being destitute of nerves—he will not allow the pain and inflammation of the arm, which sometimes are the consequences of bleeding, to proceed from the tendon or aponeurosis in that part; but attributes them to an injury done to the median nerve; or to some branch of the musculo-cutaneous nerve.—He affirms, that the phrenitis has not its seat in the dura mater, or the pleurisy in the pleura.—That in the gout, the skin and subcutaneous nerves, and not the ligaments or capsules of the joints, are the seat of pain.—There are the most important points of the Baron's system, but his opinions have been much controverted; and the late Dr Whitt, in particular, favoured the public with many tenable arguments in refutation of this doctrine, which, however, if not thoroughly received in its full extent, is now in a great measure admitted.—The ingenious Dr Hunter, who appears to have remarked the insensibility of some of these parts before the Baron's publication of his system, supposes that the Baron has gone too far in asserting, that they have absolutely no sense of feeling. He thinks that experiments on brutes are not sufficient to ascertain the more exquisite sensations of the human body; and is of opinion, that the Baron has been led into an error in surgery, in supposing that the effects of wounds of the tendons, ligaments, &c. are so very simple as to heal without any bad symptoms.—Before concluding this note, however, it is proper to observe, that some of the parts supposed by Baron Haller and others to be wholly insensible, and which really appear to be so in a sound state, have been found to acquire considerable sensibility by disease; an inattention to which circumstance has been the principal cause of that apparent contrariety of facts with which this subject has been perplexed.

(b) The growth of a new nail is a familiar instance of what is here advanced.—At its first formation it is soft, and of exquisite sensibility; but as it approaches to a harder texture, its sensibility gradually decreases, and it becomes at length capable of being cut or pared, without any appearance of pain or feeling.

(e) It is common with the generality of anatomical authors, to ascribe great sensibility to the periosteum. But this opinion is repugnant to the system mentioned in a former note; and it appears to be very probable, that this membrane, if not quite insensible, possesses, however, but a very obscure degree of feeling.

(f) Authors, who allow great sensibility to a part, consequently suppose it to be plentifully supplied with nerves.—But the nerves of the periosteum, if it contains any, have never yet been demonstrated. d, In all parts of the bones which are exposed to friction, the periosteum is wanting; as at the joints, and in the parts of the teeth which are above the sockets: it is likewise deficient wherever tendons or muscles are attached to bones; the tendons in these places performing the office of the periosteum.

e, Cartilages are covered with a membrane, called perichondrium, which, in its use and structure, resembles the periosteum.

a, The marrow is a fat, oily substance, filling the cavities of bones. That which is found in the great cavities of long bones, is of a much firmer consistence than that which is found in the cells of their spongy part. The first of these only is known by the name of marrow, the latter being usually called the medullary substance.

b, The marrow is inclosed by a very fine and transparent membrane; in some places it is of a reddish colour, where it is supplied with a great number of blood-vessels, which it receives from those of the periosteum. Anatomists file this membrane, membrana medullaris, or periosteum internum; from its lining the cavities of bones. It furnishes an infinite number of vesicular processes (c) which inclose the marrow. The medullary substance is likewise surrounded by a very delicate membrane; so that neither the marrow, nor the medullary substance, are in immediate contact with the bones.

c, There are, in the periosteum internum, vessels destined for the secretion of the marrow; and likewise absorbents which take up the oil and return it again to the circulation.

d, It is probable that the marrow is renewed by a kind of circulation. When the absorbents take up more of it than the secretory vessels are able to separate, it gradually decreases. It is for this reason, that little is found in the bones of people who die of lingering diseases.

e, The marrow was formerly supposed to be intended for the nourishment and renewal of the bones; but its oily consistence seems sufficiently to contradict this opinion. Its principal use is, probably that of preserving the bones moist (h), the natural heat of the body keeping it constantly sufficiently liquid to be infused between the bony fibres, which it may soften and render less brittle.

f, The ancients were of opinion, that the bones were more filled with marrow at the new than at the full moon. The claws of craw-fish too, which are not filled with marrow, but with actual muscles, were likewise considered as being more or less filled according to the state of the moon: but a thousand observations have convinced us of the absurdity of this and many other opinions; and we are in these days thoroughly persuaded, that the moon has no more power over the marrow of the bones, or the claws of craw-fish; than it has over an infinite number of other things which it was supposed to influence, before a taste for true philosophy took place amongst us.

a, The synovial glands are small spherical bodies (i), of the synovial and exceedingly vascular, supposed to secrete a fluid of viscid glands, a white mucilaginous nature, which serves to lubricate the joints. They are placed in small cavities in the articulations, so as to be capable of being gently compressed by the motion of the joint, which expresses their juice in proportion to the degree of friction. When the synovia is wanting, or is of too thick a consistence, the joint becomes stiff and incapable of flexion or extension. This is what is termed ankylosis. The synovia, become acrid and inflamed, is usually considered as the cause of the gout; which the Greeks have called arthritias, a word signifying a disease of the joints.

a, Ligaments are white, glistering, inelastic bands, of the ligaments, or of a compact substance, more or less broad or thick; serving to connect the bones together. They are distinguished by different names, adapted to their different forms and uses. Those of the joints are called either round or bursal. The round ligaments are white, tendinous, and inelastic. They are strong and flexible, and are chiefly found in those articulations which are capable of flexion and extension; as in the joints of the elbow and knee. The bursal or capsular ligaments, surround the whole joint like a purse, and are to be found in the articulations which allow motion every way; as in the articulation of the arm with the scapula.

a, The word skeleton, which by its etymology implies simply a dry preparation, is usually understood to signify an assemblage of all the bones of an animal united together in their natural order. It is said to be a natural skeleton, when the bones are connected together by their own proper ligaments; and an artificial one, when they are joined by means of wire.

b, The skeleton is generally divided into the head, trunk and extremities. The first division includes the bones of the cranium and face. The bones of the trunk, are the spine, ribs, sternum, and bones of the pelvis.

c, The upper extremities on each side, contain the two bones of the shoulder, viz. the scapula, and clavicle; the bone of the arm or os humeri; the bones of the fore arm; and those of the hand.

d, The lower extremities, on each side of the trunk; consist of the thigh-bone, and the bones of the leg and foot.

CHAP. II.

Of the Bones of the Head (k).

a, The head is of a roundish figure, and somewhat oval (n.)

(c) The marrow is likewise supported in these cavities by the bony filaments of the reticular substance of the bones.

(h) Havers, who has written professedly on the bones, describes the canals by which the marrow is conveyed thro' every part of their substance; and divides them into longitudinal and transverse ones. He speaks of the first as extending through the whole length of the bone; and of the latter, as the passages by which the longitudinal ones communicate with each other. The transudation of the oil through the bones of the skeleton, seems to prove that some such passages do actually exist; but it is very difficult, if not impossible, to demonstrate them satisfactorily.

(i) It is now much doubted, however, whether the appearances in the joints, which are generally called glands, are anything more than assemblages of fat.

(k) The description of the bones will be, to many readers perhaps, dry, tedious, and difficult to be understood. It is a subject which seems to preclude all attempts at variety or elegance of style. All the bones have one great use, that of inclosing and supporting the other parts of the body; and the reader may defer the reading this part of the work oval (l). Its greatest diameter is from the forehead to the occiput; its upper part is called *frons*, or the crown of the head; its anterior or fore part, is called the face; and the upper part of this is called the forehead; its posterior or hind part, is called the occiput; its sides are called the temples; and its inferior part, the basi.

b. The bones of the head may be divided into those of the cranium, and face.

Sect. i. Of the Bones of the Cranium.

a. There are eight bones of the cranium, viz., the coronal bone or os frontis; the two parietal bones or os bregmati; the os occipitis; the two temporal bones; the sphenoid bone; and the os ethmoides or cribriforme.

b. The six first are considered as proper to the cranium, and the two latter as common both to the cranium and face.

c. These bones are all harder at their surface than in their middle; and on this account they are divided into two tables, and a middle spongy substance called diploe.

a. In this, as in all the other bones, we shall consider its figure, structure, processes, depressions, and cavities; and the manner in which it is articulated with the other bones.

b. The os frontis has some resemblance in shape to the shell of the cockle. Externally it is convex, its concave side being turned towards the brain. This bone, in the places where it is united to the temporal bones, is very thin; and has there no diploe. It is likewise exceedingly thin in that part of the orbit of the eye which is nearest to the nose. Hence it is that a wound in the eye, by a sword, or any other pointed instrument, is sometimes productive of immediate death.

In these cases, the sword passing through the weak part of the bone, penetrates the brain, and divides the nerves at their origin; or perhaps, opens some blood-vessel, the consequences of which are soon fatal.

c. We observe, on the exterior surface of this bone, five apophyses or processes; which are easily to be distinguished. One of these is placed at the bottom and narrowest part of the bone, and is called the nasal process; from its supporting the upper end of the bones of the nose. The four others are called orbital processes. They serve to form the orbits, which are the cavities in which the eyes are placed. In each of these orbits there are two processes, one at the interior or great angle, and the other at the exterior, or little angle of the orbit. They are called the angular processes. Between these a ridge is extended in form of an arch, and on this the eyebrows are placed. It is called the orbital or superciliary ridge; and in some measure covers and defends the globe of the eye. This arch is interrupted near the nose by a small pit, in which the tendon of the musculus obliquus major of the eye is fixed.

ed. In each orbit, under the external process, a considerable depression is observed, in which the lachrymal gland is lodged.

d. In the anterior part of the os frontis, there is a considerable discontinuation of it, which is filled up by the cribriform part of the os ethmoides.

e. The internal view of this bone affords us an elevation in form of a ridge, which has been called the spinous process; it passes from the anterior to the posterior part of the bone, dividing it into two considerable fossae, in which the anterior lobes of the brain are placed. To this ridge is attached the extremity of the falx, as the membrane is called which divides the brain into two hemispheres. Besides these two fossae, there are many depressions which appear like digital impressions, and owe their formation to the prominent circumvolutions of the brain.

f. In young subjects the forehead is formed of two distinct bones; so that in them the sagittal future extends from the os occipitis to the nose. This bone is almost everywhere composed of two tables and a diploe. These two tables separating from each other under the eyes, form two cavities, one on each side of the face, called the frontal sinuses. These sinuses are lined with a soft membrane, called membrana pituitaria. In these sinuses a mucus is secreted, which is constantly passing, through two small holes, into the nostrils which it serves to moisten.

g. The os frontis is joined by future to many of the bones of the head, viz., to the parietal, maxillary, and temporal bones; to the os ethmoides; os sphenoides; os uncini; and os naso. The future which connects it with the parietal bones, is called the coronal future.

a. The parietal bones are two in number; they are of the parietal very thin, and even transparent in some places. The tal bone, particular figure of each of these bones, is that of an irregular square, bordered with indentations thro' its whole circumference, except at its lower part. It will be easily conceived that these bones, which compose the superior and lateral parts of the cranium, and cover the greatest part of the brain, form a kind of vault. On their inner surface we observe the marks of the vessels of the dura mater.

b. The os parietalia, are joined to each other by the sagittal future; to the os sphenoides, and os temporum, by the squamos future; to the os occipitis, by the lambdoidal future (m); so called from its resemblance to the Greek letter lambda; and to the os frontis, by the coronal future.

c. In new-born infants, the os parietalia are separated from the middle of the divided os frontis, by a portion of the cranium then unossified. When the finger is applied to this part, which is called the fontanelle, the dilatation of the brain, and of the vessels of the dura mater, may be easily felt. And in midwifery, the feel of this part, which, in natural labours, is

work till he meets with a skeleton.—That part, however, which relates to the teeth is excepted, as being a branch which ought to be understood by every body, independent of the skeleton.

(l) The bones of the fetus being perfectly distinct, and the muscles in young persons not acting much, the shape of the head is supposed to depend much on the management of children, when very young. Vesalius, who has remarked the difference in people of different nations, observes for instance, that the head of a Turk is conical, from the early use of the turban; whilst that of an Englishman is flattened by the chin-strap.

(m) The lambdoidal future is sometimes very irregular; being composed of many small futures, which surround so many little bones called os trigonum, tho' sometimes improperly, as they are not always triangular. is the first to present itself, is an indication of the state of the fetus, whether it be living or dead. Every blow on this part, in children, is liable to be attended with the most fatal consequences; and it is not without reason, that experienced nurses cautiously defend it from injury, by applying a linen cloth to it several times doubled.

a. The occipital bone forms the posterior and inferior parts of the skull; it approaches near to the shape of a lozenge, and is indented throughout three parts of its circumference.

b. There is a considerable hole in the inferior portion of this bone, called the foramen magnum; thro' which the medulla oblongata passes into the spine. The nervi acceffiorii, and vertebral arteries, likewise pass thro' it. Besides this, there are usually four other holes peculiar to this bone, and two which are common to it and the os temporum; these foramina serve for the passage of the blood-vessels and nerves. At the sides, and a little on the anterior part of the foramen magnum, are two processes called the condyles, one on each side; they are of an oval figure, and are covered with cartilage.

c. The external surface of this bone, which is very irregular, affords attachment to several muscles. On looking over its internal surface, we perceive the appearance of a crest, formed by a very prominent ridge; which rises upwards from near the foramen magnum, and by two transverse sinuities, one on each side of the ridge. This crest occasions the formation of four fossae, two above and two below the sinuities. In the latter are placed the lobes of the cerebellum; and in the former, the posterior lobes of the brain. The two sinuities serve to receive the lateral sinuses.

d. In the upper part of this bone is seen a continuation of the sinuity of the longitudinal sinus. The cuneiform process (which is the name given to the great apophysis at the fore part of this bone) is made concave for the reception of the medulla oblongata.

e. The occipital bone is thicker and stronger than either of the other bones of the head, tho' irregularly so; at its inferior part where it is thinnest, it is covered by a great number of muscles.

f. The reasons for so much thickness and strength in this bone seem to be, that it covers the cerebellum, in which the least wound is of the utmost consequence; and, that it is by its situation more liable to be fractured by falls than any other bone of the cranium. For if we fall forwards, the hands are naturally put out to prevent the forehead's touching the ground; and if to one side, the shoulders in a great measure protect the sides of the head; but if a person falls backwards, the hinder part of the head consequently strikes against the earth, and that too with considerable violence. Nature then has wisely constructed this bone so as to be capable of the greatest resistance.

g. The os occipitis, is joined by means of the cuneiform process to the sphenoid bone, with which it often unites and makes but one bone in those who are advanced in life. It is connected to the parietal bones by the lambdoidal sutures; and to the temporal bones, by the addiments of the same nature. This head is likewise united to the trunk by means of this bone. The two condyles of the occipital bone, are received into the superior oblique processes of the first vertebrae of the neck; and it is by means of this articulation that a certain degree of flexion and extension, or rather of motion of the head forwards and backwards, is performed. We say a certain degree of motion, because that which is performed on the first vertebra alone, and independent of the other vertebrae, is very insensible.

h. In flexion, the vertebrae form a kind of bow, and freighten themselves again in extension.

a. There are two temporal bones, one on each side. Of the tempora they are usually divided into two parts, one of which is called the squamosus, or scaly part; and the other os petrosum, from its inequality and hardness. This last is shaped like a pyramid.

b. In both these parts there are processes and cavities to be described; externally there are three processes, one anterior, called the zygomatic process; one posterior, called the mastoid or mamillary process, from its resemblance to a nipple; and one inferior, called the styloid process, because it is shaped like a stiletto, or dagger.

c. The cavities are, 1. The meatus auditorius externus. 2. A large fossa which serves for the articulation of the lower jaw; it is before the meatus auditorius, and immediately under the zygomatic process. 3. The stylo-mastoid hole, so called from its situation between the styloid and mastoid processes; it is likewise styled the aqueduct of Fallopian, and affords a passage to the portio dura of the auditory, or seventh pair of nerves. 4. Below, and on the fore part of the last foramen, we observe part of the jugular fossa; a thimble-like cavity, in which the beginning of the internal jugular vein is lodged. Anterior and superior to this fossa, is the orifice of a foramen through which the carotid artery passes. This conduit runs first upwards and then forwards, forming a kind of elbow, and terminates at the end of the os petrosum; at this part of each of the os temporum we observe the opening of the Eustachian tube, a canal which passes from the ear to the mouth.

d. In examining the internal surface of these bones, we remark the triangular figure of their petrous part which separates two fossae; one superior and anterior, the other inferior and posterior; the latter of these composes part of the fossa, in which the cerebellum is placed; and the former, a portion of the least fossa for the basis of the brain; on the posterior side of the os petrosum, we observe the meatus auditorius internus, into which enters the double nerve of the seventh pair, viz. the portio dura, and portio mollis of that pair.

e. The os petrosum contains several little bones called the bones of the ear; which, as they do not enter into the formation of the cranium, shall be described when we are treating of the organs of hearing.

f. The os temporum are joined to the os malarum by the zygomatic sutures; to the parietal bones by the lambdoidal sutures; to the os occipitis by the lambdoidal sutures; and, to the sphenoid bone by the suture of that name.

g. The os sphenoides, or cuneiforme as it is sometimes called from its wedge-like situation amidst the other bones of the head, is of a more irregular figure than any other bone. It has been compared to a bat with its wings extended. This resemblance is but faint, but it would be difficult perhaps to find anything it resembles more.

b. We b, We distinguish in this bone its body or middle part, and its wings or sides, which are much more extensive than its body.

c, On whatever side we view it, we discover only processes and cavities. The processes, both external and internal, are so very numerous, that it will be sufficient for us to describe the principal ones, of which there are three on the outside: one of these is in the middle, and is shaped like a crest, making part of the septum narium; the other two are the pterygoid or aliform processes, one on each side of the body of the bone, and at no great distance from it; each of these processes is divided into two wings; and of these the exterior one is the widest; the other terminates in a hook-like process.

d, This bone on its inner surface affords three fossae, two of which are considerable ones; they are formed by the wings of the bone, and make part of the lesser fossa of the basis of the skull. The third, which is smaller, is on the top of the body of the bone, and is called fossa turcica; from its resemblance to a Turkish saddle. This fossa, in which the pituitary gland is placed, has posteriorly and anteriorly processes, called the clinoid processes.

e, There are eight holes in this bone, viz. four on each side; several pair of nerves and some blood vessels pass through them.

f, Within the substance of the os sphenoides, there are two sinuses separated by a bony plate. They are lined with the pituitary membrane; and like the frontal sinuses, separate a mucus which passes into the nostrils.

g, The os sphenoides is joined to all the bones of the cranium, and likewise to the os maxillaria, osseous lamina, osseous palati, and vomer.

h, This bone makes part of the basis of the skull, serves to form in some measure the orbits, and affords attachment to several muscles.

a, The os ethmoides, or sieve-like bone, as it is called from the great number of small holes with which it is pierced, is placed in the anterior part of the basis of the skull, and is the last bone that enters into the composition of the cranium. It is nearly of a cubical figure.

b, There are three parts to be described in this bone, viz. one in the middle, and two at its sides; the middle part, from which it derives its name, is a thin lamella, or bony table, pierced with an infinite number of holes, through which pass as many filaments of the olfactory nerve. From the middle of this plate, both on the outside and from within, there rises up a process which is easily observed. The inner one is called cribriformis; from its supposed resemblance to a cock's comb; to this process the falx is attached, which divides the brain into two hemispheres. The exterior process, which has the same common basis as the cribriformis, is a fine lamella, which is united to the vomer, and divides the cavity of the nostrils, tho' unequally; it being usually inclined to one side or other.

c, The lateral parts of this bone are composed of a cellular substance, and these cells are so very intricate, that their figure or number cannot be described. Many writers have on this account, called this part of the bone the labyrinth. These cells are externally covered with bony laminae, thin like the cells themselves, but very smooth and plain. This part of the bone is called os planum; and forms part of the orbit.

d, The different cells of this bone, which are exceedingly numerous, and which are everywhere lined with the pituitary membrane, evidently serve to enlarge the cavity of the nose in which the organ of smelling resides.

e, This bone is joined to the os sphenoides, os frontis, osseous maxillaria, osseous palati, osseous naso, osseous uncus, and vomer.

f, The ancients, who considered the brain as the seat of all the humours, were of opinion, that this viscus discharged its redundant moisture through the holes of the ethmoid bone. But in these times they only can adopt so erroneous a notion, who have not exact ideas of the human anatomy. The vulgar still think that abscesses of the brain discharge themselves through the mouth and ears, and that snuff is liable to get into the head; but neither snuff, nor the matter of an abscess, are more capable of passing thro' the cribriform bone, than the serosity which they supposed was discharged thro' it in a common cold; all the holes of the ethmoid bone are filled up with branches of the olfactory nerve. Its inner part is likewise covered with the dura mater, and its cells are everywhere lined with the pituitary membrane; so that neither matter, nor any other fluid can possibly pass through this bone either externally, or internally. Matter is, indeed, sometimes discharged through the nostrils; but the seat of the disease is in the sinuses of the nose, and not in the brain; and impromptuations are observed to take place in the ear, which suppurate and discharge themselves externally.

g, Before we leave the bones of the head, we wish to make some general observations on its structure and figure. As the cranium might have been composed of a single bone, the articulation of its several bones being absolutely without motion, it may be asked, perhaps, why such a multiplicity of bones, and so great a number of sutures? Many advantages may possibly arise from this plurality of bones and sutures, which have not yet been observed. We are able, however, to point out many useful ends which could only be accomplished by this peculiarity of structure: in this, as in all the other works of nature, the great wisdom of the Creator is evinced, and cannot fail to excite our admiration and gratitude.

h, The cranium, by being divided into several bones, grows much faster and with greater facility than if it was composed of one piece only. In the fetus, the bones as we have before observed, are perfectly distinct from each other. The ossification begins in the middle of each bone, and proceeds gradually to the circumference. Hence the ossification, and of course the increase of the head, is carried on from an infinite number of points at the same time; and the bones consequently approach each other in the same proportion. To illustrate this doctrine more clearly, if it can want further illustration; suppose it necessary for the parietal bones, which compose the upper part of the head, to extend their ossification, and form the fore part of the head likewise; is it not evident, that this process would be much more tedious than it is now, when the os frontis and the parietal bones are both growing at the same time? Hence it happens that the heads of young people, in which the bones begin to touch each other, increase, crease slowly; and that the proportionate increase of the volume of the head is greater in three months in the fetus, than it is perhaps in 24 months, at the age of 14 or 15 years.

i. The futures, exclusive of their advantages in suspending the processes of the dura mater, are evidently of great utility to prevent the too great extent of fractures of the skull. Suppose, for instance, that by a fall or blow, one of the bones of the cranium becomes fractured. The fissure which, in a head composed of only one bone would be liable to extend itself through the whole of it, is stopped by the first future it meets, and the effects of the injury are confined to the bone on which the blow was received.

k. The spherical shape of the head seems likewise to render it more capable of resisting external violence than any other shape would do. In a vault the parts mutually support and strengthen each other; and this happens in the cranium.

Sect. ii. Of the Bones of the Face.

a. The face, which consists of a great number of bones, is usually divided into the upper and lower jaws; of these the latter is capable of motion, but the former is immovable. The bones of the upper jaw are thirteen in number, exclusive of the teeth, which we shall describe separately, after having finished the other bones of the head. Of these thirteen bones, there are six on each side of the maxilla superior, or upper jaw; and one in the middle.

b. The bones, which are in pairs, are the os maxillare; os maxillare; os nasi; os unguis; os palati; and os spongiosum inferius. The single bone is the vomer.

c. The os maxillare are the prominent square bones which form the upper part of the cheeks; they are situated close under the eyes, and make part of the orbits. Each of these bones have three surfaces to be considered. One of these is exterior and somewhat convex; the second is superior and concave, serving to form the lower and lateral parts of the orbit. The third, which is posterior, is very unequal, and concave for the lodgment of the lower part of the temporal muscle.

d. Each of these bones may be described as having four processes formed by their four angles. Two of these may be called orbital processes. The superior one is united by future to the os frontis, and that below, to the maxillary bone. The third is connected with the os sphenoides by means of the transverse future; and the fourth is joined to the zygomatic process of the temporal bone, with which it forms the zygoma.

e. These bones are so called, because they constitute the most considerable portion of the upper jaw. They are two in number, and generally remain distinct throughout life. Their figure is exceedingly irregular, and not easily to be described.

f. Of the many processes which are to be seen on these bones, and which are connected with the bones of the face and skull, we shall describe only the most remarkable.

g. One of these processes is at the upper and forepart of the bone, making part of the side of the nose, and called the nasal process. Another forms a kind of circular sweep at the inferior part of the bone, in which are the alveoli, or sockets for the teeth; this is called the alveolar process. A third process is united to the os maxillare on each side. The alveolar process has, posteriorly, a considerable tuberosity on its internal surface, called the maxillary tuberosity.

h. There are two horizontal lamellae behind the alveolar process, which uniting together, form part of the roof of the mouth, and divide it from the nose. This partition, being seated somewhat higher than the lower edge of the alveolar process, gives the roof of the mouth a considerable hollowness.

i. In viewing these bones internally, we observe a fossa in the inferior portion of the nasal process; which with the os unguis, forms a passage for the lachrymal duct.

j. Where these two bones are united to each other, they project somewhat forwards, leaving between them a furrow which receives the inferior portion of the septum nasi.

k. Each of these bones is hollow, and forms a considerable sinus under its orbital part. This sinus, which is usually called antrum highanum, is lined with the pituitary membrane, it answers the same purposes as the other sinuses of the nose; and communicates with the nostrils, by an opening which appears to be a large one in the skeleton, but in the recent subject is much smaller.

l. The os maxillare, not only serve to form the cheeks, but likewise the palate, nose, and orbits; and besides their union with each other, they are connected with the greatest part of the bones of the face and cranium, viz. with the os nasi, os malarum, os unguis, os palati, os frontis, os sphenoides, and os ethmoides.

m. The os nasi resemble two irregular squares. They are narrower and thicker above than below; externally they are somewhat convex, and internally a little concave. These bones constitute the upper part of the nose; at their fore part they are united to each other; above to the os frontis; by their sides to the os maxillare superius; posteriorly and interiorly, to the septum narium; and below to the cartilages which compose the rest of the nostrils.

n. These bones derive their name from their transparency, and figure which resembles that of a finger-nail; they are likewise styled os lacrymalis, because they help to form, with the nasal process of the os maxillare superius on each side, an excavation for the lodgment of the lachrymal sac; and to compose part of the lachrymal duct through which the tears pass into the nostrils.

o. These bones, which are the smallest bones of the face, are of an irregular shape; and may be described as having two smooth parts, divided by a middle ridge on their external surface. One of these parts which is flat, forms a small part of the orbit; the other, which is next to the nose, is concave, and makes, as we have before observed, part of the lachrymal duct; by its union with the canal formed by the nasal process of the superior maxillary bone. That part of the bone which forms the duct is cribriform, being pierced with a great number of holes.

p. Each of these bones is joined to the os maxillare superius, os frontis, and os ethmoides.

q. These bones are of a very irregular figure; they are placed at the back part of the roof of the mouth, palat. and serve to form the nasal and maxillary fossa, and a small portion of the orbit. Where they are united to each other they rise up into a spine on their internal surface; this spine appears to be a continuation of that of the superior maxillary bones, and helps to form the septum narium.

b. These bones are joined to the os maxillaria superiores, os sphenoides, os ethmoides, and vomer.

a. This bone derives its name from its resemblance to a plough-share. It is a long and flat bone, somewhat thicker at its back than at its fore part. At its upper part we observe a furrow extending through its whole length. The back of this furrow which is the largest, receives a process of the sphenoid bone; from this the furrow advances forwards, and becoming narrower and shallower, receives some part of the nasal lamella ethmoides; the rest serves to support the middle cartilage of the nose.

b. The inferior portion of this bone is placed on the nasal spine of the maxillary and palate bones, which we mentioned in our description of the os palati.

c. The vomer is united to the os sphenoides, os ethmoides, os maxillaria superiores, and os palati. It forms part of the septum narium, by dividing the back part of the nose into two nostrils.

Of the os sphenoides inferiores:

a. The parts which are usually described by this name, do not seem to deserve to be distinguished as distinct bones. They consist of a spongy lamella in each nostril, which is united to the spongy lamina of the ethmoid bone, of which they are by some considered as a part.

b. Each of these lamellae is longest from behind forwards; with its convex surface turned towards the septum narium, and its concave part towards the maxillary bone, covering the opening of the lacrimal duct into the nose.

c. These bones are covered with the pituitary membrane; and, besides their connection with the ethmoid bone, are joined to the os maxillaria superiores; os palati; and os unguis.

Of the maxilla inferior, or lower jaw; which in its figure resembles a bow with its end elevated; is at first composed of two distinct bones; but these soon after birth unite into one at the middle of the chin, so as to form only one bone. The superior edge of this bone has, like the maxilla superior, a process called the alveolar process. This as well as that of the upper jaw to which it is in other respects a good deal similar, is likewise furnished with cavities for the reception of the teeth.

b. The posterior part of the bone on each side rises almost perpendicularly into two processes, one of which is called the coronoid, and the other the condyloid process. The first of these is the highest; it is thin and pointed, and the temporal muscle which is attached to it, serves to elevate the jaw. The condyloid process is narrower, thicker, and shorter than the other; terminating in an oblong rounded head, which is made for a moveable articulation with the cranium, and is received into a fossa of the temporal bone. In this joint there is a movable cartilage, which being more closely connected to the condyle than to the cavity, may be considered as belonging to the former. At the bottom of each coronoid process, on its inner part, is a foramen or canal, which extends under the roots of all the teeth, and terminates at the outer surface of the bone near the chin. Each of these foramina affords a passage to an artery, vein, and nerve, which send of branches to the several teeth.

c. This bone is capable of a great many motions. The condyles, by sliding from the cavity towards the eminences on each side, bring the jaw horizontally forwards, as in the action of biting; or the condyles only may be brought forwards while the rest of the jaw is tilted backwards, as in the case when the mouth is open. The condyles may also slide alternately backwards and forwards, from the cavity to the eminence, and vice versa; so that, while one condyle advances, the other moves backwards, turning the body of the jaw from side to side, as in grinding the teeth. The great use of the cartilages seems, to be that of securing the articulation, by adapting themselves to the different inequalities in these several motions of the jaw, and to prevent any injuries from friction. This last circumstance is of great importance where there is so much motion; and Mr J. Hunter has accordingly found this cartilage in the different tribes of carnivorous animals where there is no eminence nor cavity, nor other apparatus for grinding.

d. The alveolar processes are formed of an external and internal plate united together by thin bony partitions, which divide the processes at the fore part of the jaw into as many sockets as there are teeth; but at the posterior part where the teeth have more than one root, each root has a distinct cell. These processes in both jaws begin to be formed with the teeth, accompany them in their growth, and disappear when the teeth fall; so that the loss of the one seems constantly to be attended with the loss of the other.

a. The teeth are bones of a particular structure, formed for the purposes of mastication, and the articulation of the voice.

b. Each tooth may be divided into its body, neck, and root, or fangs. The body of the tooth is that part which appears above the gums. The root is fixed into the socket, and the neck is the middle part between the two. The teeth are composed of two substances, viz., enamel, and bone. The enamel, or as it is sometimes called, the vitreous, or cortical part of the tooth, is a very hard and compact substance, of a white colour, and peculiar to the teeth. When broken, it appears fibrous or striated; and all the striae are directed from the circumference to the center of the tooth. This enamel is thickest on the grinding surface, becoming gradually thinner as it approaches the neck, where it terminates insensibly. Rupich affirmed, that he could trace the arteries into the hardest part of the teeth; Lewenhoek suspected the fibres of the enamel to be so many vessels; and, Monro says, he has frequently injected the vessels of the teeth in children so as to make the inside of the cortex appear perfectly red. But Mr J. Hunter who has written professedly on the teeth, says, that no injection will ever reach this substance; that it receives no tinge from madder; and that it has no marks of being vascular, or of having a circulation of fluids.

c. The bony part of a tooth resembles other bones in its structure, but is much harder than the most compact part of bones in general. It composes the inner part of the body, neck and root of the tooth. From certain certain circumstances (n) this part of a tooth appears to be vascular, but there are many others which tend to prove that it is not.

d, Each tooth has an inner cavity, which beginning by a small opening, becomes larger and terminates in the body of the tooth.

e, This cavity is supplied with an artery, vein, and nerve, which pass through the small hole in the root. In old people this hole sometimes closes, and the tooth becomes then insensible.

f, The teeth are invested with a periosteum from their fangs to a little beyond their bony sockets, where it is attached to the gums. This membrane seems to be common to the tooth which it incloses, and to the sockets which it lines.

g, The teeth are likewise secured in their sockets by a red substance called the gums, which everywhere covers the alveolar processes, and has as many perforations as there are teeth. The gums are exceedingly vascular, and have something like a cartilaginous hardness and elasticity, but do not seem to have much sensibility. The gums of infants, which perform the offices of teeth, have a hard ridge extending through their whole length, but in old people who have lost their teeth this ridge is wanting.

h, The number of the teeth in both jaws at full maturity, usually varies from 28 to 32. They are commonly divided into three classes, viz. incisors, canines, and grinders, or molars (o). The incisors are the four teeth in the fore part of the jaws; they derive their name from their use in dividing and cutting the food, and have each of them two surfaces which meet in a sharp edge. Of these surfaces, the anterior one is convex, and the posterior one somewhat concave. In the upper jaw they are usually broader and thicker, especially the two first, than those of the under jaw, over which they generally fall by being placed a little obliquely.

i, The canines are the longest of all the teeth, deriving their name from their resemblance to a dog's tusks (r.) There is one of these teeth on each side of the incisors, so that there are two in each jaw. Their fang differs from that of the incisors, only in being much larger; and their shape may be easily described to be that of an incisor with its edge worn off so as to end in a narrow point instead of a thin edge.

k, These teeth not being calculated for dividing like the incisors, or for grinding, seem to be intended for laying hold of substances (q).

l, The grinders, or molars, of which there are ten in each jaw, are so called, because from their size and figure they are calculated for grinding the food. The canines and incisors have only one fang, but the three last grinders in the under jaw have constantly two fangs; and the same teeth in the upper jaw three fangs. Sometimes these fangs are divided into two points near their base, and each of these points has, perhaps, been sometimes considered as a distinct fang. The grinders likewise differ from each other in their appearance. The two first on each side, which Mr Hunter appears to have distinguished very properly by the name of bicuspids, seem to be of a middle nature, between the incisors and grinders; and have sometimes only one root. The two beyond these on each side are much larger. The last grinder is shorter and smaller than the rest, and from its coming through the gums later than the rest, and sometimes not appearing till late in life, is called dens sapientiae. The variation in the number of teeth usually depends on the dentes sapientiae.

m, There is in the structure and arrangement of all

(n) These circumstances are, that the teeth like other bones are liable to swellings; and that they are found anchylosed with the socket. But Mr J. Hunter supposes that both these may be original formations. He never saw the vessels of the teeth injected in any preparation, either of young or old subjects; and as the most convincing proof of their not being vascular, he reasons from the analogy between them and other bones. He observes, for instance, that in a young animal that has been fed with madder, the parts of the teeth which were formed before it was put on the madder diet will appear of their natural colour, but that such parts as were formed while the animal was taking the madder will be of a red colour, whereas in other bones, the hardest parts are susceptible of the dye, tho' more slowly than the parts which are growing. Hence, he supposes, that the teeth when completely formed cease to be vascular. Again, he tells us, that if you leave off feeding the animal with madder a considerable time before you kill it, you will find the above appearances still subsisting, with this addition, that all the parts of the teeth which were formed after leaving off the madder will be white. This experiment proves, that a tooth once ting'd does not lose its colour, whereas other bones do (tho' very slowly) return again to their natural appearance; and as the dye in this case must be taken into the habit by the absorbent, he is led to suspect that the teeth are without absorbents as well as other vessels. Tho' from these and other reasons, they seem to appear as extraneous bodies with respect to a circulation thro' their substance, yet they most certainly possess a living principle. They are not easily affected by the diseases to which other bones are liable. They do not become soft in a mollifies osium, nor is their growth evidently retarded in rickety children; but they are, as we often experience, exquisitely sensible; and are capable of being transplanted into other sockets when recently drawn. This sensibility evidently arises from the exposure of the nerve in a cavity of the tooth; and their disposition to unite with the sockets into which they are transplanted, tho' a proof of their living principle (for a tooth that has been long drawn before it is transplanted, and which of course has lost this principle will never become fixed) does not absolutely prove their having a circulation.

(o) Mr Hunter has thought proper to vary this division. He retains the old name of incisors to the four fore teeth, but he distinguishes the canine teeth by the name of the cuspidati. The two teeth which are next to these, and which have been usually ranked with the molars, he calls the bicuspides; and he gives the name of grinders only, to the three last teeth on each side.

(p) The canine teeth of the upper jaw are likewise sometimes called eye teeth, from their supposed connection with the eyes, and the great danger to which the eye-light is thought to be exposed by their being drawn. Although these are vulgar notions, real evils are sometimes occasioned by extracting them. They are separated from the maxillary sinus, only by a very thin bony partition; this partition is liable to be injured in the operation, and the pituitary membrane being in this case torn, inflammation and the most disagreeable consequences have often ensued.

(q) Mr Hunter remarks of these teeth, that we may trace in them a similarity in shape, situation and use, from the most imperfectly carnivorous animal, which we believe to be the human species, to the lion, which is the most perfectly carnivorous. these teeth an art which cannot be sufficiently admired.

To understand it properly, it will be necessary to consider the under jaw as a kind of lever, with its fixed points at its articulations with the temporal bones: it will be right to observe too, that its powers arise from its different muscles, but in elevation chiefly from the temporalis; and that the aliment constitutes the object of resistance. It will appear then that the molares, by being placed nearest the centre of motion, are calculated to press with a much greater force than the other teeth, independent of their grinding powers, and that it is for this reason we put between them any hard body we wish to break.

n. The canini and incisores, are placed farther from this point, and of course cannot exert so much force; but they are made for cutting and tearing the food; and this form seems to make amends for their deficiency in strength.

o. There are examples of children who have come into the world with two, three, and even four teeth; but these examples are very rare, and it is seldom before the seventh, eighth or ninth month after birth that the incisores begin to pass through the gum. The symptoms of dentition, however, in consequence of irritation from the teeth, frequently take place in the fourth or fifth month. One of the incisores usually appears first in the lower jaw, and is followed by one in the upper jaw; and so on alternately, till these eight teeth are cut after this: the child continues easy during one, two, or three months, when the symptoms of irritation take place again; and continue till about the eleventh or twelfth month, when one and sometimes two of the canini begin to appear at a time, but most usually in succession. Here then are twelve teeth in the first year.

p. About the seventeenth, eighteenth, or twentieth month, and sometimes later, two of the molares appear in each jaw, and enable children to take solid nourishment.

q. We all know the danger to which children are exposed during the time of dentition; and we shall not be surprized at it, if we consider that every tooth before it makes its appearance must pass through a bony lamella which covers the socket; and likewise thro' the periosteum and gums.

r. The symptoms are more or less alarming, in proportion to the resistance which these parts afford to the teeth; and, according to the number of teeth which may chance to seek a passage at the same time. Were they all to appear at once, children would fall victims to the pain and excessive irritation; but nature has so very wisely disposed them, that they usually appear one after the other, with some distance of time between each.

s. About the age of two years, four other dentes molares usually appear; four others in the fourth or fifth year, and four more about the seventh year. These make up the twenty-eight teeth, which continue to be the number till the twentieth, twenty-second, or twenty-fifth year; and sometimes later, when four more grinders make their appearance, and these are the dentes sapientiae. These teeth have been in some instances cut at the age of eighty years; and it sometimes happens that they do not appear at all. This then is the number of teeth, and the order in which they appear; but it is to be observed, that about the seventh, eighth, ninth or tenth year; sometimes a little sooner, sometimes later, the incisores begin to fall out of their sockets; and that, between the seventh and fourteenth year, not only the incisores, but likewise the canini, and sometimes the four first molares, making in all twenty teeth, are shed, and their place supplied by others of a firmer texture, with larger fangs, which remain till they become affected by disease, or fall out in old age. The first teeth are called the temporary or milk teeth, to distinguish them from the adult teeth. The rudiments of both these series of teeth are originally formed together in the fetus, and are to be seen in the jaws of very young subjects in two rows, and in a distinct set of alveoli; so that it is not by the growing of one tooth under another in the same socket, that the uppermost tooth is mechanically pushed out, as is perhaps commonly imagined; but the temporary teeth, and those which are to succeed them, being as we have just now observed, placed in separate alveoli; the upper sockets gradually disappear, as the under ones increase in size, till at length the teeth they contain having no longer any support, consequently fall out.

Sect. iii. Of the Os Hyoides. (R).

a. The os hyoides which is placed at the root of the tongue, was so called by the ancients on account of its supposed resemblance to the Greek letter Η.

b. It will be necessary to distinguish in it, its body, horns, and appendices.

c. The body is the middle and broadest part of the bone, so placed that it may be easily felt with the finger in the fore part of the throat. Its fore part is irregularly convex, and its inner surface unequally concave. The cornua or horns, which are flat and a little bent, are considerably longer than the body of the bone, and may be said to form the sides of the os. The appendices, or little horns, as they are called by M. Winiford and some other writers, are two processes which rise up from the articulations of the cornua with the body, and are usually connected with the styloid process on each side by means of a ligament.

d. This bone serves to support the tongue, and affords attachment to a variety of muscles, some of which perform the motions of the tongue, and others act on the larynx and fauces.

Chap. III.

Of the Bones of the Trunk.

a. The trunk of the skeleton is composed of the spine, the thorax, and the pelvis.

Sect. i. Of the Spine.

a. The spine is a long bony column, in figure not much unlike the letter S, which extends from the head to the lower part of the trunk, and is the great support of the whole body. b, It is made of a great number of bones called vertebrae.

c, It may be considered as being composed of two irregular pyramids, which are united to each other in that part of the loins where the last of the lumbar vertebrae is united to the os sacrum.

d, The vertebrae which form the upper and longest pyramid, are called true vertebrae; and those which compose the lower pyramid, are termed false vertebrae; because they do not in every thing resemble the others; and particularly, because in the adult state they become perfectly immovable, whilst the upper ones continue to be capable of motion; for it is upon the bones of the spine that the body turns, and their name has its derivation from the Latin verb vertere, which signifies to turn.

e, The vertebrae are likewise divided into five classes, viz. 1. The cervical or vertebrae of the neck; 2. the dorsal or vertebrae of the back; 3. the lumbar or vertebrae of the loins; 4. the os sacrum; and, 5. the coccyx.

f, We will first point out what these bones, and especially the true vertebrae, have in common with each other; and then separately describe these five classes.

g, In each vertebra, as in all other bones, it will be necessary to remark the body of the bone, its processes, and cavities.

h, The body of one of the vertebrae may be compared to part of a cylinder cut off transversely: convex before, and concave at its posterior surface where it makes part of the cavity of the spine.

i, Each vertebra has commonly seven processes.

k, The first of these is, the spinous process, which is placed at the back part of the vertebra, and gives the name of spine to the whole of this bony canal; two others are called transverse processes, from their situation with respect to the figure of the spine; and are placed on each side of the spinous process. The four others which are called oblique or articular processes are much smaller than the other three; there are two of these on the upper, and two on the lower part of each vertebra, rising from near the basis of the transverse processes. They are called articular processes, because they are articulated with each other; that is, the two superior processes of one vertebra, are articulated with the two inferior processes of the vertebra above it; and they are called oblique processes from their situation with respect to the processes with which they are united; these oblique processes are articulated to each other by a species of gingulum, and each process is covered at its articulation with cartilage.

l, There is in every vertebra, between its body and apophyses, a foramen large enough to admit a finger. These foramina correspond with each other through all the vertebrae, and form a long bony conduit for the lodgment of the spinal marrow.

m, Besides this great hole, there are four notches on each side of every vertebra, between the oblique processes and the body of the vertebra; two of these notches are at the upper, and two at the lower part of the bone; each of the inferior notches meeting with one of the superior notches of the vertebra below it, forms a foramen; whilst the superior notches do the same with the inferior notches of the vertebra above it. These four foramina, form passages for blood vessels, and for the nerves that pass out of the spine: the vertebrae are united together by means of a cartilaginous substance, which forms a kind of partition between the several vertebrae; these cartilages are thicker and more flexible between the lumbar vertebrae than in other parts of the spine; the most considerable motions of the trunk being performed on these vertebrae. These cartilages being very elastic, the extension and flexion of the body, and its motion backwards and forwards, or to either side, are performed with great facility. This elasticity seems to be the reason why people who have been long standing, or have carried a considerable weight, are found to be shorter than when they have been long in bed. In the two first instances, the ligaments are evidently more exposed to compression than when we are in bed in an horizontal posture.

n, The change which takes place in these cartilages in advanced life, occasions the decrease in stature, and the stooping forwards which are usually to be observed in old people. The cartilages then become shrivelled, and consequently lose in a great measure their elasticity.

o, Besides this connection of the several vertebrae by means of these cartilages, there are likewise particular ligaments which unite the several bones to each other; and the periosteum externum, the membrane which incloses the marrow, and the muscles which are attached to the spine, all serve to strengthen this union.

p, We may venture to remark, that all the vertebrae diminish in density and firmness of texture in proportion as they increase in size; so that the lower vertebrae, though larger, are not so heavy as those above them; in consequence of this mode of structure, the size of the vertebrae is increased without adding to their weight; and this is an object of no little importance in a part of the body, which besides flexibility and suppleness, seems to require lightness as one of its essential properties.

q, In very young children, each vertebra is composed of three bony pieces connected by cartilages which afterwards ossify.

r, There are seven vertebrae of the neck; they are of a firmer texture than the other bones of the spine. The transverse processes of these vertebrae are forked for the lodgment of muscles; and, at the bottom of each of these processes, there is a foramen for the passage of the cervical artery and vein. The first and second of these vertebrae must be described more particularly. The first approaches almost to an oval shape; on its superior surface it has two cavities, which admit the condyles of the occipital bone with which it is articulated. This vertebra which is called Atlas, from its supporting the head, cannot well be described as having either body or spinous process, being a kind of bony ring. Anteriorly where it is articulated to the odontoid process of the second vertebra, it is very thin.

s, The second vertebra which is called dentata, has at its upper and anterior part, a process called the odontoid process; from its resemblance to a large tooth, which is articulated with the atlas; to which this second vertebra may be said to serve as an axis.

t, It is commonly observed that the head turns to the right or left upon this vertebra; but this supposition seems to be erroneous.

u, The face cannot turn the quarter of a circle, that is, to the shoulder, upon this vertebra alone, without being liable to injure the spinal marrow, which would probably probably be divided transversely by the first vertebra; so that all the seven vertebrae seem to concur in this motion when it is in any considerable degree.

a, We have nothing particular to observe in these vertebrae, which are twelve in number; except two lateral depressions in the sides of each vertebra, and another in each transverse process, by means of which these bones are articulated with the ribs.

b, These five vertebrae differ only from those of the back, in their being larger; and in having their spinous processes at a greater distance from each other. The most considerable motions of the trunk are made on these vertebrae; and these motions could not be performed with so much ease, were the processes placed nearer to each other.

c, The os sacrum which is composed of five or six pieces in young subjects, becomes one bone in more advanced age.

d, It is nearly of a triangular figure, its inferior portion being bent a little forwards. Its superior part has two oblique processes which are articulated with the last of the lumbar vertebrae, and it has likewise a small spinous process. Its concave or anterior side has many prominences, which are filled up and covered with the muscular and tendinous parts behind.

e, This bone has five pair of holes, which afford a passage to the blood vessels, and likewise to the nerves which are derived from the spinal marrow; for the marrow is continued even in the os sacrum.

f, This bone is united laterally to the os innominata or hip-bones, and below to the coccyx.

g, The coccyx, which like the os sacrum, is in young people made up of several distinct parts, usually becomes one bone in the adult state.

h, It serves to support the intestine rectum; and, by its being capable of some degree of motion at its articulation with the sacrum, and being like that bone bent forwards, we are enabled to sit with ease.

i, This bone is about three inches long; it is broadest at its upper part, and from thence grows narrower to its apex, where it is not bigger than the little finger.

j, This bone, which has got its name from its supposed resemblance to a cuckow's beak; differs very much from the vertebrae, being usually without processes, and having no cavity for the medulla spinalis, or foramina for the passage of nerves.

k, The spine, of which we have now finished the anatomical description, is destined for many and important uses. The medulla oblongata is lodged, in its bony canal, secure from external injury; it defends the thoracic and abdominal viscera; it serves to support the head, and gives a general firmness to the whole trunk.

l, We have before compared it to the letter S, and its different turns will be found to render it not very unlike the figure of that letter.

m, In the neck we see it projecting somewhat forwards to support the head, which, without this affiance, would require a greater number of muscles; through the whole length of the thorax it is carried in a curved direction backwards; and thus adds considerably to the cavity of the chest, and consequently affords more room to the lungs, heart, and large blood vessels. In the loins, the spine again projects forwards in a direction with the centre of gravity; by which means the body is easily kept in an erect posture; for otherwise we should be liable to fall forwards. But at its inferior part, it again recedes backwards, and helps to form a cavity called the pelvis; in which the urinary bladder, intestine rectum, and other viscera are placed.

n, Whoever contemplates and clearly understands the structure of this part of the human body, cannot but acknowledge that it is admirably adapted to the uses to which it is destined; and that it is evidently the work of a divine author.

o, If this bony column had been formed only of one piece, it would have been much more easily fractured than it is now; and, by confining the trunk to a stiff situation, a variety of motions would have been altogether prevented, which are now performed with ease by the great number of bones of which it is composed.

p, It is firm, and yet to this firmness there is added a perfect flexibility. If it is required to carry a load upon the head, the neck becomes stiff with the affiance of its muscles, and accommodates itself to the load as if it was composed only of one bone. In stooping likewise, or in turning to either side, the spine turns itself in every direction, as if all its bones were separated from each other.

q, In a part of the body which is composed of so great a number of bones, and constructed for such a variety of motion as the spine is, luxation is more to be expected than fracture; and this is very wisely guarded against in every direction, by the many processes which are to be found in each vertebra; and by the cartilages, ligaments, and other means of connection, which we have described as uniting them together.

Sect. ii. Of the Bones of the Thorax.

a, The thorax, or chest, is composed of many bones, viz. the sternum, which is placed at its anterior part; twelve ribs on each side which make up its lateral parts; and the dorsal vertebrae, which constitute its posterior part. These last have been already described.

b, The sternum is the long bone which extends itself from the upper to the lower part of the breast anteriorly, and to which the ribs and the clavicles are articulated.

c, In children it is composed of several bones united by cartilages; but as we advance in life, most of these cartilages ossify, and the sternum in the adult state is found to consist only of two pieces; and sometimes becomes one bone. It is, however, generally described as being composed of two parts; one superior, which is broad, thick, and short; and one inferior, which is thinner, narrower, and longer than the other.

d, It terminates at its lower part by a cartilage, which is called the xiphoid, or sword-like cartilage; from its supposed resemblance to the point of a sword; but its shape is much more like that of a myrtle leaf.

e, We have already observed, that this bone is articulated with the clavicle on each side; it is likewise joined to the fourteen true ribs; viz. seven on its right, and seven on its left side.

f, The ribs are bones shaped like a bow, which compose the sides of the chest. There are twelve on each side. They are distinguished into true and false ribs; the seven upper ribs, which are articulated to the sternum, are called true ribs; and the five lower ones, which are are not immediately attached to that bone, are called false ribs.

b. On the inferior and anterior surface of each rib, we observe a sinuosity for the lodgment of an artery, vein, and nerve.

c. The ribs are not bony through their whole length, their anterior part being cartilaginous. They are articulated with the vertebrae and sternum; every rib, or at least the greatest number of them, has at its posterior part, two processes; one at its extremity, by means of which it is articulated with the body of two vertebrae; and another, which is a very evident tuberosity, by which it is articulated with the transverse process of the lowest of these two vertebrae; the first rib is not articulated by its extremity to two vertebrae, being simply attached to the upper part of the first vertebra of the back; the seven superior or true ribs, are articulated anteriorly with the sternum by their cartilages; but the false ribs are supported in a different manner; the eighth, which is the first of these ribs, being attached by its cartilage to the seventh; the ninth to the eighth, &c.

d. The two lowest ribs differ likewise from all the rest in the following particulars: they are articulated with the body of a vertebra, and not with a transverse process; and, anteriorly, their cartilage is loose, not being attached to the cartilages of the other ribs; and this seems to be, because the most considerable motions of the trunk are not performed on the lumbar vertebrae alone, but likewise on the two last vertebrae of the back; so that if these two ribs had been confined anteriorly like the rest, and likewise attached to the bodies of two vertebrae, and to the transverse process, this disposition would have impeded the motion of the two last vertebrae of the back, and consequently affected the motion of the trunk in general.

e. The ribs serve to cover and secure the vital organs, viz., the heart and lungs; without this bony defense, these viscera would be constantly exposed to interruption, and perhaps to injury; which would not fail to be extremely prejudicial to health and even to life; for the functions of those organs are so essential to life, that we cannot long exist without them.

Sect. ii. Of the Bones of the Pelvis.

a. The pelvis is composed of the os sacrum, os coccygis, and two ossa innominata. The two first of these bones were included in our account of the spine, to which they more properly belong.

b. Each os innominatum in children, is composed of three distinct bones; but as they advance in life, the marks of this separation gradually disappear, by the ossification of the cartilages by which they were united to each other, and they become one bone; still, however, continuing to retain the names of ilium, ischium, and pubis, by which their divisions were originally distinguished; and to be described as three distinct bones by all anatomical writers. The os ilium forms the upper and largest part of the bone, the os ischium its posterior and inferior portion, and the os pubis its anterior part.

c. The os ilium is articulated posteriorly to the os sacrum, by a firm cartilaginous substance; and is united to the os pubis before, and to the os ischium below; its superior portion is thin, and terminates in a ridge called the crista or spine of the ilium, and more commonly known by the name of the haunch. This crista rises up like an arch, being turned somewhat outwards; and from this appearance, the upper part of the pelvis when viewed together, has not been improperly compared to the wings of a phaeton.

b. Externally, this bone is unequally prominent and hollowed for the attachment of muscles, and internally, it is smooth and concave; at its lower part there is a considerable ridge on its inner surface. This ridge which extends from the os sacrum, and corresponds with a similar prominence both on that bone and the ischium, forms with the inner part of the os pubis, what in midwifery is understood to be the brim of the pelvis.

c. The os ilium has likewise a smaller surface posteriorly, by which it is articulated to the os sacrum.

d. The crista, or spine, which is originally an epiphysis, has two considerable tubercles; one anteriorly, and the other posteriorly which is the largest of the two; the ends of this spine too, from their projecting more than the parts of the bone below them, are called spinal processes; before the anterior spinal process, the spine is hollowed where part of the fatorial muscle is placed; and below the posterior spinal process there is a very large niche in the bone which is the recent subject; has a strong ligament stretched over its lower part from the os sacrum, to the sharp pointed process of the ischium, so that a great hole is formed, through which pass the great sciatic nerve, and the posterior crural vessels under the pyriform muscle, part of which is likewise lodged in this hole.

a. The os ischium, which is a bone of a very irregular figure, is usually divided into its body, tuberosity, and ramus. The body externally forms the inferior and greatest part of the acetabulum; and sends a sharp pointed apophysis backwards, called the spine of the ischium. This is the process to which the ligament is attached, which we just now described as forming a great foramen for the passage of the sciatic nerve. The tuberosity is large and irregular, and is placed at the inferior part of the bone, giving origin to several muscles. The tuberosity which is the lowest portion of the trunk, supports us when we sit; from this tuberosity the bone becoming narrower and thinner forms the ramus or branch, which passing forwards and upwards, makes with the ramus of the os pubis a large hole, called the foramen ovale; this hole which is closed by a membrane, affords through its whole circumference attachment to muscles.

a. The os pubis which is the smallest of the three Os pubis, bones, is placed at the forepart of the pelvis, where it is united to the os pubis of the other side, by means of a very strong cartilage, and constitutes what is called the symphysis pubis. This bone is distinguished by the body, angle, and ramus. The body, which is the outer part, is joined to the os ilium. The angle comes forwards to form the symphysis, and the ramus is a thin apophysis, which is united to the ramus of the ischium.

b. The three bones we have described as constituting the os innominatum on each side, all concur to form the great acetabulum or cotyloid cavity, which receives the head of the thigh-bone. A little fossa is to be observed in this cavity, in which are placed the mucilaginous glands which serve to lubricate the joint, and facilitate its motions. We are able likewise to discover the impression made by the round ligament, which by being attached both to this cavity and to the head of the os femoris, helps to secure the latter in the acetabulum.

c. The bones of the pelvis serve to lodge the intestines, urinary bladder, and other viscera; and likewise to unite the trunk to the lower extremities: but besides these uses they are defined in the female subject, for other and more important purposes; and the accoucheur finds in the study of these bones, the great foundation of all midwifery knowledge.

CHAP. IV. Of the Extremities.

a. This part of the osteology is divided into the upper and lower extremities. We will begin with the first of these.

Sec. i. Of the Upper Extremity.

a. This consists of the shoulder, arm, and hand.

§ 1. Of the Bones of the Shoulder.

a. The shoulder is composed of two bones, the clavicle and scapula.

b. The clavicle or collar bone, so called from its resemblance to the key in use amongst the ancients; is a little curved at both its extremities like an Italic f. This bone is about the size of the little finger, but longer, and being of a very spongy substance is very liable to fracture. At its interior part where it is round and thickest, it is articulated to the sternum; and its posterior part, which is flatter and broader than the other, is connected to a process of the scapula called acromion.

b. The clavicle serves to regulate the motions of the scapula, by preventing its being brought too much forwards, or carried too far backwards. It affords attachment to several muscles, and helps to cover and protect the subclavian arteries which derive their name from their situation under this bone.

a. The scapula which approaches nearly to a triangular figure, is fixed not unlike a buckler to the posterior part of the true ribs. It is of a very unequal thickness, and like all other broad, flat bones, is somewhat cellular. Externally it is convex, and internally concave, to accommodate itself to the convexity of the ribs. We observe in this bone three unequal sides. The largest of the three called the bony, is turned towards the vertebrae. Another which is less than the former, is below this; and the third which is the least of the three, is at the upper part of the bone. Externally the bone is elevated into a considerable spine, which rising small at the base of the scapula, becomes gradually higher and broader; and divides the outer surface of the bone into two fossa. The superior of these, which is the smallest, serves to lodge the supra spinatus muscle; and the inferior fossa which is much larger than the other, gives origin to the infra spinatus. This spine terminates in a broad and flat process at the top of the shoulder, called the processus acromion, to which the clavicle is articulated. This process is hollowed at its lower part, to allow a passage to the supra and infra spinati muscles. This bone has likewise another considerable process at its superior part, which from its resemblance to the beak of a bird, is called the coracoid process. From the external side of this coracoid process, a strong ligament passes to the processus acromion; which prevents a luxation of the os humeri upwards.

b. The scapula is articulated to the clavicle and os humeri, to which last it serves as a fulcrum; and by altering its position, it affords a greater scope to the bones of the arm in their different motions. It likewise affords attachment to several muscles, and posteriorly serves as a defence to the thorax.

§ 2. Of the Bones of the Arm.

a. The arm is commonly divided into two parts, which are articulated to each other at the elbow. The upper part retains the name of arm properly so called, and the lower part is usually called the fore arm.

Art. i. Of the Arm properly so called.

a. The arm is formed of a single bone, called os humeri. This bone which is almost of a cylindrical form, may be divided into its body and its extremities.

b. The upper extremity terminates in a large round smooth head, which is admitted into the glenoid cavity of the scapula.

c. The lower extremity has many processes and cavities. The principal processes are its two condyles, one exterior and the other interior, and of these the last is the largest; between these two we observe two lateral protuberances, which together with a middle cavity, form as it were a kind of pulley upon which the motions of the fore arm are chiefly performed. At each side of the condyles, as well exteriorly as interiorly, there is another eminence which affords attachment to several muscles of the hand and fingers. Posteriorly and superiorly, speaking with respect to the condyles, we observe a deep fossa which receives a considerable process of the ulna; and anteriorly, and opposite to this fossa, we observe another which is much less, and receives another process of the same bone.

d. The body of the bone has, at its upper and anterior part, a furrow which begins from behind the head of the bone, and serves to lodge the tendon of a muscle. The body of the os humeri is hollow through its whole length; and like all other long bones, has its marrow.

e. The humerus is articulated at its upper part to the scapula. This articulation, which allows motion every way, is surrounded by a capsular ligament. Its lower extremity is articulated with the bones of the arm.

Art. 2. Of the Fore Arm.

a. The fore arm is composed of two bones, the ulna and radius.

b. The ulna, or elbow bone, is much less than the humerus, and becomes gradually smaller as it descends to the wrist. At its upper part it has two processes and two cavities. Of the two processes, the largest, which is situated posteriorly and called the olecranon, is admitted into the posterior fossa of the humerus. The other process is placed anteriorly, and is called the coronoid process. In bending the arm it enters into the anterior fossa of the humerus. This process being much smaller than the other, permits the fore arm to bend inwards; whereas the olecranon, which is shaped like a hook, reaches the bottom of its fossa in the humerus. as soon as the arm becomes straight; and will not permit the fore arm to be bent backwards. The ligaments likewise oppose this motion.

b. Between the two processes which we have described, there is a considerable cavity called the sigmoid cavity; and divided into two fossae by a small eminence which passes from one process to the other; it is by means of this cavity and the two processes, that the ulna is articulated with the humerus by gingilimus.

c. At the bottom of the coronoid process inferiorly, there is a small sigmoid cavity, which serves for the articulation of the ulna with the radius.

d. The body of the ulna is of a triangular shape, its lower extremity terminates by a small head and a little styloid process. The ulna is articulated above to the os humeri both above and below to the radius; and to the wrist at its lowest extremity. All these articulations are secured by means of ligaments.

a. The radius is placed at the inside of the forearm; it is somewhat larger than the ulna, but not quite so long as that bone. Its upper part is cylindrical, hollowed superiorly to receive the outer condyle of the os humeri laterally; it is admitted into the little sigmoid cavity of the ulna, and the cylindrical part of the bone turns in this cavity in the motions of pronation and supination (a). This bone follows the ulna in flexion and extension, without at all assisting in those motions. The lower extremity of the radius is much larger and stronger than its upper part; the ulna, on the contrary is smaller and weaker below than above, so that they serve to supply each others deficiencies in both these parts.

b. On the external side of this bone, we observe a small cavity which is destined to receive the lower end of the ulna; and its lowest part is formed into a larger cavity, by means of which it is articulated with the bones of the wrist. This bone supports the two first bones of the wrist on the side of the thumb, whereas the ulna is articulated with that bone of the wrist which corresponds with the little finger.

c. Thro' the whole length both of this bone and the ulna, a ridge is observed, which affords attachment to an interosseous ligament. This ligament fills up the space between the two bones.

Art. 3. Of the Hand.

a. The carpus or wrist, includes eight bones, disposed in two ranks. Anatomical writers have not only usually described the particular figure of these several bones; but have likewise given to each of them a different name.

b. Such minute in this part of the osteology, seem to be unnecessary in this work; and we shall only observe, that they are articulated with the radius and ulna, and likewise with the bones of the forearm by means of several ligaments.

a. The metacarpus consists of four bones, which support the fingers; externally they are a little convex, and internally somewhat concave, where they form the palm of the hand. They are hollow, and of a cylindrical shape.

b. At each extremity they are a little hollowed for their articulation superiorly with the bones of the carpus, and inferiorly with the first phalanx of the fingers, in the same manner as the several phalanges of the fingers are articulated with each other.

a. Every body knows the number and the names of the fingers. The five fingers of each hand are composed of 15 bones, disposed in three ranks called phalanges. The bones of the first phalanx, which are articulated with the metacarpus, are the largest; and those of the last phalanx, are the smallest. All these bones are larger at their extremities than in their middle part.

b. We observe at the extremities of the bones of the carpus, metacarpus, and fingers, several inequalities which serve for their articulation with each other; and these articulations are strengthened by means of the ligaments which surround them.

c. It will be easily understood that this multiplicity of bones in the hand (for there are 27 in each hand), is essential to the different motions we wish to perform. If each finger was composed only of one bone instead of three, it would be impossible for us to grasp anything.

Sec. ii. Of the Lower Extremities.

a. Each lower extremity is divided into four parts, viz.: The os femoris, or thigh bone; the rotula or knee pan; the leg, and the foot.

§. 1. Of the Os Femoris.

a. The thigh is composed only of this bone, which is larger and stronger than any other bone of the body. It will be necessary to distinguish its body and extremities. Its body, which is of a cylindrical shape, is convex before and concave behind; where it serves to lodge several muscles. Throughout two thirds of its length, we observe a ridge called linea aspera, which affords insertion to the triceps muscle.

b. At its upper extremity, we must describe the neck and head of the bone, and likewise two considerable processes. The head, which forms the greater portion of a sphere unequally divided, is turned inwards, and is received into the great cotyloid cavity of the os innominatum; at this part of the bone, there is a little fossa to be observed to which the round ligament is attached; and which we have already described as tending to secure the head of this bone in the great acetabulum. The neck is almost horizontal, considered with respect to its situation with the body of the bone. Of the two processes, the external one, which is the largest, is called trochanter major; and the other, which is placed on the inside of the bone, is called trochanter minor; they both afford attachment to muscles. The articulation of the os femoris with the trunk, is strengthened by means of a capsular ligament, which is attached everywhere to the surface of the great cotyloid cavity of the os innominatum, and surrounds the head of the bone.

c. The os femoris moves upon the trunk in every direction.

d. At the lower extremity of the bone are two processes, called the condyles; and an intermediate cavity, by means of which it is articulated with the leg by gingilimus.

e. Between the condyles, there is a cavity posteriorly

(a) The motions of pronation and supination may be easily described. If the palm of the hand, for instance, is placed on the surface of a table, the hand will be said to be in a state of pronation; but if the back part of the hand is turned towards the table, the hand will then be in a state of supination. ly in which the blood vessels and nerves are placed secure from the compressions to which they would otherwise be exposed in the action of bending the leg; and which would not fail to be hurtful.

f. At the side of each condyle externally there is a tuberosity; from whence the lateral ligaments originate which are attached to the tibia.

g. A ligament likewise arises from each condyle posteriorly, one of which passes from the right to the left, and the other from the left to the right; so that they intersect each other; and are called the cross ligaments.

h. The lateral ligaments prevent the motion of the leg upon the thigh to the right or left, and the cross ligaments, which are also attached to the tibia, prevent its being bent forwards.

i. In new-born children all the processes of this bone are cartilaginous.

§ 2. Of the Rotula.

a. The rotula, patella, or knee-pan, as it is differently called; is a bone about four or five inches in circumference, which in some measure resembles the common figure of the heart with its point downwards, and is placed at the fore part of the joint of the knee.

b. It is thicker in its middle part than at its edge; anteriorly it is smooth, and a little convex; its posterior surface, which is more unequal, affords an elevation in the middle which is admitted between the two condyles of the os femoris.

c. This bone is retained in its proper situation by a ligament which everywhere surrounds it, and is attached both to the tibia and os femoris; and likewise by the tendons of several muscles, which do not however prevent its sliding from above downwards, and from below upwards.

d. In very young children this bone is entirely cartilaginous.

e. The use of this bone seems to be, to defend the articulation of the knee from external injury; it likewise tends to increase the power of the muscles which act in the extension of the leg, by removing their direction farther from the centre of motion in the manner of a pulley.

§ 3. Of the Leg.

a. The leg is composed of two bones; of these the inner one, which is the largest, is called tibia; the other is much smaller, and is called the fibula.

b. At the lower and inner portion of the tibia, we observe a considerable process called malleolus internus; the basis of the bone terminates in a large transverse cavity, by which it is articulated with the uppermost bone of the foot; it has likewise another cavity at its lower end and outer side; which is somewhat oblong, and receives the lower end of the fibula.

c. The tibia is hollow through its whole length.

a. The fibula is a small long bone, placed on the outside of the tibia; its upper extremity does not reach quite so high as that part of the tibia, but its lower end extends somewhat lower; both above and below, it is articulated with the tibia by means of the lateral cavities which we observed in our description of that bone.

b. Its lower extremity is stretched out into a coronoid process, which is flattened at its inside, and is convex externally, forming what is called the malleolus externus, or outer ankle; this is rather lower than the leolus internus of the tibia.

c. The body of this bone, which is irregularly triangular, is a little hollowed at its internal surface, which is turned towards the tibia; and it affords like that bone, through its whole length, attachment to a ligament, which from its situation is called the interosseous ligament.

§ 4. Of the Bones of the Foot.

a. The bones of the foot, as well as those of the hand, are usually described in three divisions, but with different names; in the hand we spoke of the carpus, metacarpus, and fingers; but the divisions of the foot are called the tarus, metatarsus, and toes.

Art. 1. Of the Tarus.

a. The tarus is composed of seven bones, viz. The astragalus, os calcis, os naviculare, os cuboides, and three others called cuneiform bones.

b. The astragalus is a considerable bone, with which both the tibia and fibula are articulated; it is the uppermost bone of the foot, and has several surfaces to be considered. Its upper, and somewhat posterior part, which is smooth and convex, is admitted into the cavity of the tibia; its lateral parts are connected with the malleoli of the two bones of the leg; below, it is articulated with the os calcis; and its anterior surface is received by the os naviculare; all these articulations are secured by means of ligaments.

a. The os calcis, or calcaneum, which is the largest bone of the foot, is of a very irregular figure; behind, it is formed into a considerable tuberosity called the heel; without this tuberosity which supports us in an erect posture, and when we walk, we should be liable to fall backwards.

b. On the interval surface of this bone, we observe a considerable sinuosity which affords a passage to the tendon of a muscle; and to the posterior part of the os calcis a strong tendinous cord called tendo achillis (s) is attached, which is formed by the tendons of several muscles united together; the articulation of this with the other bones is secured by means of ligaments.

a. The os naviculare, or scaphoides (for these two terms have the same signification), is so called on account of its resemblance to a little bark. At its posterior part,

(s) This tendon is sometimes ruptured by jumping, dancing, or other violent efforts. part, which is concave, it receives the astragalus; anteriorly it is articulated with the cuneiform bones, and laterally it is connected with the os cuboides.

a, The os cuboides forms an irregular cube. Posteriorly it is articulated with the os calcis; anteriorly it supports the two last bones of the metatarsus; and laterally it joins the third cuneiform bone and the os navicularis.

a, Each of these bones, which are three in number, resembles a wedge, and from this similitude their name is derived. They are placed next to the metatarsus by the sides of each other, and are usually distinguished into os cuneiforme externum, medium or minimum, and internum or maximum. The superior surface of these bones, from their wedge-like shape, is broader than that which is below, where they help to form the sole of the foot; posteriorly they are united to the os navicularis, and anteriorly they support the three first metatarsal bones.

b, The os cuneiforme externum is joined laterally to the os cuboides.

c, These bones complete our account of the tarus; and though what we have said of this part of the osteology has been very simple and concise, yet, many readers may not clearly understand it; but if they will be pleased to view these bones in their proper situation in the skeleton, all that we have said of them will be easily understood.

Art. 2. Of the Metatarsus.

a, The metatarsus is made up of five bones, whereas the metacarpus consists only of four. The cause of this difference is, that in the hand, the last bone of the thumb is not included among the metacarpal bones, whereas in the foot the great toe has only two bones. The first of these bones supports the great toe, and is much larger than the rest, which nearly resemble each other in size.

EXPLANATION OF THE PLATES OF OSTEOLGY.

Plate XIII.

Figure 1. A Male Skeleton.

A, Os frontis. B, Os parietale. C, Os temporum. D, Os occipitis. E, Os naso. F, Os maxillare superius. G, Os maxillare inferius. H, Os mandibulae. I, The teeth, which are sixteen in each jaw. K, The seven vertebrae of the neck, with their intermediate cartilages. L, The twelve dorsal vertebrae, with their intermediate cartilages. M, The five lumbar vertebrae, and N, Their intermediate cartilages. O, Os sacrum. P, Os coccygis. Q, Os ilium. R, Os pubis. S, Os ischium. T, The seven true ribs. U, The five false ribs. V, The sternum. X, The clavicle. Y, The scapula. Z, The os humeri. a, Ulna. b, Radius. c, The eight bones of the carpus. d, The five metacarpal bones. e, The phalanges of the fingers. f, The os femoris. g, The patella. h, The tibia. i, The fibula. k, The seven bones of the tarus. l, The five metatarsal bones. m, The phalanges of the toes.

Fig. 2. The internal view of the Os Frontis.

a, The superior serrated edge, which assists to form the coronal suture. b, The external angular process. c, The internal angular process. d, The nasal process. e, The orbital process. f, The frontal sinus. g, The sagittal suture, which (as here) is sometimes continued to the nose.

Vol. I.

Fig. 3. The internal side of the left Parietal bone.

a, Its superior edge, which, joined with the other, forms the sagittal suture. b, The anterior edge, which assists in the formation of the coronal suture. c, The inferior edge for the squamous suture. d, The posterior edge for the lambdoid suture. e, A depression made by the lateral sinus. f, The prints of the principal artery of the dura mater.

Fig. 4. The internal view of the Occipital bone.

a, The two sides, which assist to form the lambdoid suture. b, The extremity of the cuneiform process, where it joins the sphenoid bone. c, The two condyloid processes, which articulate the head with the spine. d, The prints made by the posterior lobes of the brain. e, The prints made by the lobes of the cerebellum. f, The cruciform ridge. g, The foramen magnum, thro' which the spinal marrow passes. h, The foramen magnum, for the passage of the ninth pair of nerves.

Fig. 5. The internal side of the right Temporal bone.

a, The upper edge which forms the squamous suture. b, The pars mammillaris. c, The pars petrota. d, The zygomatic process. e, The styloid process. f, The entry of the auditory nerve.

Fig. 6. Fig. 6. The internal view of the Sphenoid bone. a, The temporal processes. b, The pterygoid processes. c, The spinous processes. d, The posterior clinoid processes. e, The anterior clinoid processes. f, The sella turcica, for lodging the glandula pituitaria. g, The anterior process, which joins the ethmoid bone.

Fig. 7. The exterior view of the Ethmoid bone. a, The pars plana, which forms part of the orbit. b, The os spongiosum superius. c, The nasal lamella. d, The ethmoid cells. e, Cribrum galli.

Fig. 8. The posterior view of the Ossa Nas. a, Their superior sides. b, Their inferior sides. c, Their exterior sides. d, Their joining.

Fig. 9. The side of the Os Uncus next to the nose. a, The orbital part. b, The lacrimal part. c, The furrow between these two convex parts.

Fig. 10. The posterior view of the right Os Maxill. a, The superior orbital process. b, The inferior orbital process. c, The malar process. d, The zygomatic process. e, The internal orbital process.

Fig. 11. A view of the lower part, and side next to the nose, of the right Os Maxillare, with the Palate-bone, and Os Spongiosum Inferius. a, The nasal process. b, The tuber, at the top of which is the orbital process, and within it, k, The antrum maxillare. c, The nasal spine. d, The os spongiosum inferius. e, The palate-plate. f, The os palatinum. g, The two dentes incisores. h, The dens caninus. i, The five dentes molares.

Fig. 12. The right Palate-Bone. a, The palate-plate. b, The pterygoid process. c, The nasal lamella. d, The orbital process.

Fig. 13. A view of the side next to the mouth of the left side of the lower jaw. a, The substance in the middle of the chin. b, The base. c, The angle. d, The coronoid process. e, The condyloid process. f, The entry of the nerve and blood-vessels. g, The five molars.

Fig. 14. A Tooth cut perpendicularly. a, The fibres of the enamel. b, The osseous part. c, The entry at the point of the root, to d, The channel for the nerve and blood-vessels.

Fig. 15. A view of the interior surface of the Base of the Skull. A A A, The two tables of the skull, with the diploe. B B, The orbital processes of the frontal bone. C, The cribrum galli, with the cribriform-plate of the ethmoid bone on each side of it. D, The cuneiform process of the os occipitis. E, The cruciform ridge. F, The foramen magnum for the passage of the medulla spinalis. G, The zygoma, made by the joining of the zygomatic processes of the os temporum and occipitis. H, The pars squamosa of the os temporum. I, The pars mammillaris. K, The pars petrosa. L, The temporal process of the sphenoid bone. M, The anterior clinoid process of the right side. N, The posterior clinoid process of the right side, and between them, O, The sella Turcica. 1, The foramen opticum of the left side. 2, The foramen lacerum. 3, The foramen rotundum.

Fig. 16. The frontal, occipital, sphenoid, and ethmoid bones, being cut perpendicularly thro' the middle, and the nasal, maxillary, and palate bones separated from each other, the interior view of the left side of the Cranium, and bones of the Upper Jaw, are represented. A A, The two tables and diploe of the frontal and occipital bones. B, The coronal suture. C, The serrated edges of the parietal, for forming the sagittal future. D, The lambdoid suture. E, The squamosus suture. F, The furrows made by the vessels of the dura mater. G, The frontal sinus. H, The cribrum galli. I, The nasal lamella of the ethmoid bone. K, The temporal process of the sphenoid bone. L, The sella turcica. M, The sphenoid sinus. N, The vomer. O, The palate-plate of the superior maxillary bone; and from it the processus alveolaris, which contains the teeth. P, The os nasi. Q, The passage into the left nostril. r, The meatus auditorius internus for the passage of the auditory nerve. s, The passage of the ninth pair of nerves. t, The foramen incisivum.

Fig. 17. The external surface of the base of the Cranium and Upper Jaw. A A, The lambdoid suture. B, The superior horizontal ridge of the occipital bone, which is opposite to the cruciform ridge, where the superior longitudinal sinus divides to form the lateral sinuses. C, The perpendicular ridge. D, The inferior horizontal ridge. E, The foramen magnum, for the passage of the medulla spinalis. FF, The two condyles. G, The cuneiform process. H H, The zygomatic process of the temporal bone. II, The mastoid processes. K, The vomer, which forms the back-part of the septum nasi. LL, The styloid processes. MM, The fossa at the root of the mastoid processes, for the posterior belly of the digastric muscle. NN, The cavities for receiving the condyles of the lower jaw. OO, The osa palatini. P, The longitudinal palate-suture. Q, The transverse palate-suture. R, The alveoli, or spongy sockets for the teeth. S, The zygomatic process of the osa palatini. TT, The zygomatic suture. u, Meatus auditorius externus. v, Hole for the internal carotid artery. w, For the artery of the dura mater. x, Foramen ovale, for the third branch of the fifth pair, to the upper jaw.

Plate XIV.

Fig. 1. A posterior view of the Sternum and Clavicles, with the ligament connecting the clavicles to each other. a, The posterior surface of the sternum. b b, The broken ends of the clavicles. c c c c, The tubercles near the extremity of each clavicle. d, The ligament connecting the clavicles.

Fig. 2. A fore view of the Left Scapula, and of a half of the Clavicle, with their ligaments. a, The spine of the scapula. b, The acromion. c, The inferior angle. d, Inferior costa. e, Cervix. f, Glenoid cavity, covered with cartilage for the arm-bone. g, The capsular ligament of the joint. h, Coracoid process. i, The broken end of the clavicle. k, Its extremity joined to the acromion. l, A ligament coming out single from the acromion to the coracoid process. m, A ligament coming out single from the the acromion, and dividing into two, which are fixed to the coracoid process.

Fig. 3. The joint of the elbow of the Left Arm, with the ligaments.

a, The os humeri. b, Its internal condyle. c, The two prominent parts of its trochlea appearing through the capsular ligament. d, The ulna. e, The radius. f, The part of the ligament including the head of the radius.

Fig. 4. The Bones of the Right-hand, with the Palm in view.

a, The radius. b, The ulna. c, The scaphoid bone of the carpus. d, The os lunare. e, The os cuneiforme. f, The os pisiforme. g, Trapezium. h, Trapezoides. i, Capitatum. k, Unciforme. l, The four metacarpal bones of the fingers. m, The first phalanx. n, The second phalanx. o, The third phalanx. p, The metacarpal bone of the thumb. q, The first joint. r, The second joint.

Fig. 5. The posterior view of the bones of the Left Hand.

The explication of Fig. 4, serves for this figure; the same letters pointing out the same bones, though in a different view.

Fig. 6. The upper extremity of the Tibia, with the semilunar cartilages of the joint of the knee, and some ligaments.

a, The strong ligament which connects the rotula to the tubercle of the tibia. b, The parts of the extremity of the tibia, covered with cartilage, which appear within the semilunar cartilages. c, The semilunar cartilages. d, The two parts of what is called the crois ligament.

Fig. 7. The posterior view of the joint of the Right Knee.

a, The os femoris cut. b, Its internal condyle. c, Its external condyle. d, The back-part of the tibia. e, The superior extremity of the fibula. f, The edge of the internal semilunar cartilage. g, An oblique ligament. h, A larger perpendicular ligament. i, A ligament connecting the femur and fibula.

Fig. 8. The anterior view of the joint of the Right Knee.

b, The internal condyle. c, Its external condyle. d, The part of the os femoris, on which the patella moves. e, A perpendicular ligament. f, The two parts of the cruciate ligaments. g, The edges of the two moveable semilunar cartilages. h, The tibia. i, The strong ligament of the patella.—k, The back part of it where the fat has been dissected away. l, The external depression. m, The internal one. n, The cut tibia.

Fig. 9. A view of the inferior part of the bones of the Right Foot.

a, The great knob of the os calcis. b, A prominence on its outside. c, The hollow for the tendons, nerves, and blood-vessels. d, The anterior extremity of the os calcis. e, Part of the astragalus. f, Its head covered with cartilage. g, The internal prominence of the os naviculare. h, The os cuboides. i, The os cuneiforme internum; k, Medium; l, Externum. m, The metatarsal bones of the four lesser toes. n, The first—o, The second—p, The third phalanx of the four lesser toes. q, The metatarsal bones of the four lesser toes. r, The first—s, The second joint.

Fig. 10. The inferior surface of the two large Sesamoid Bones, at the first joint of the great toe.

Fig. 11. The superior view of the bones of the Right Foot.

a, b, as in Fig. 9. c, The superior head of the astragalus. d, &c., as in Fig. 9.

Fig. 12. The view of the Sole of the Foot with its ligaments.

a, The great knob of the os calcis. b, The hollow for the tendons, nerves, and blood-vessels. c, The sheaths of the flexores pollicis, and digitorum longi opened. d, The strong cartilaginous ligament supporting the head of the astragalus. e, h, Two ligaments which unite into one, and are fixed to the metatarsal bone of the great toe. f, A ligament from the knob of the os calcis to the metatarsal bone of the little toe. g, A strong triangular ligament, which supports the bones of the tarbus. i, The ligaments of the joints of the five metatarsal bones.

Fig. 13. a, The head of the thigh bone of a child. b, The ligamentum rotundum connecting it to the acetabulum. c, The capsular ligament of the joint with its arteries injected. d, The numerous vessels of the mucilaginous gland injected.

Fig. 14. The back view of the cartilages of the Larynx, with the Os Hyoides.

a, The posterior part of the base of the os hyoides. b, Its cornua. c, The appendix of the right side. d, A ligament sent out from the appendix of the left side, to the styloid process of the temporal bone. e, The union of the base with the left cornu. f, The posterior sides of (g) the thyroid cartilage. h, h, Its superior cornua. i, i, Its inferior cornua. k, The criroid cartilage. l, The arytenoid cartilages. m, The entry into the lungs, named glottis. n, The epiglottis. o, o, The superior cartilages of the trachea. p, Its ligamentous back-part.

Fig. 15. The superior concave surface of the Sesamoid Bones at the first joint of the great toe, with their ligaments.

a, Three sesamoid bones. b, The ligamentous substance in which they are formed.

Part II. Of the Soft Parts in General;

And

Of the Common Integuments.

A Natomical writers usually proceed to a description of the muscles after having finished the osteology; but we shall deviate a little from the common method, with a view to describe every thing clearly. ly and distinctly, and to avoid a tautology which would otherwise be unavoidable. All the parts of the body are so intimately connected to each other, that it seems to be impossible to convey a just idea of any one of them, without being in some measure obliged to say something of others; and on this account, we wish to mention in this place, the names and situation of the principal viscera of the body; that when mention is hereafter made of any of them in the course of this treatise, the reader may at least know where they are placed.

b, After this little digression, the common integuments, and after them the muscles, will be described; we then propose to enter into an examination of the several viscera and their different functions. In describing the brain, occasion will be taken to speak of the nerves and animal spirits. The circulation of the blood will follow the anatomy of the heart, and the secretions and other matters will be introduced in their proper places.

c, The body is divided into three great cavities. Of these,

d, The uppermost is formed by the bones of the cranium, and includes the brain and cerebrum.

e, The second is composed of the vertebrae of the back, the sternum and true ribs, with the additional assistance of muscles, membranes and common integuments, and is called the thorax. It contains the heart and lungs. The third and inferior cavity is the abdomen. It is separated from the thorax by means of the diaphragm, and is formed by the lumbar vertebrae, the os sacrum, the os innominata, and the false ribs; to which we may add the peritoneum, and a variety of muscles. This cavity includes the stomach, intestines, omentum or cawl, liver, pancreas, spleen, kidneys, urinary bladder, and parts of generation.

f, Under the division of common integuments, are usually included the epidermis, or scarf skin; the reticulum mucosum of Malpighi; the cutis, or true skin; and the membrana adiposa. The hair and nails, as well as the miliary and sebaceous glands, may be considered as appendages to the skin.

**CHAP. I.**

Of the Epidermis.

a, The epidermis, cuticle or scarf skin, is a fine, transparent, and infensible pellicle; destitute of nerves and blood-vessels, which invests the body, and everywhere covers the true skin. This scarf skin which appears to be very simple, is composed of several laminae or scales, which are increased by pressure, as we observe in the hands and feet; where it is frequently much thickened, and becomes perfectly callous. It may be separated from the true skin by heat, or by maceration in water (t). Some anatomical writers have supposed that it is formed by a humidity exhaled from the whole surface of the body, which gradually hardens when it comes into contact with the air. They were perhaps induced to adopt this opinion, by observing the speedy regeneration of this part of the body when it has been by any means destroyed; it appearing to be renewed in all parts of its surface at the same time, whereas other parts which have been injured, are found to direct their circumference only towards their center; but a demonstrative proof that the epidermis is not a viscid humour hardened by means of the external air, is, that the fetus in utero is found to have this covering. Its true origin seems to be from the expansion of the extremities of the excretory vessels, which are found everywhere on the surface of the true skin (u). And this formation seems to explain the cause of its quick growth.

b, It is pierced with an infinite number of pores, or little holes, which afford a passage to the hairs, sweat, and infensible perspiration; and likewise to warm water, mercury, and whatever else is capable of being taken in by the absorbents of the skin. The lines which we observe on the epidermis belong to the true skin. The cuticle adjusts itself to them, but does not form them.

**CHAP. II.**

Sect. i. Of the Reticulum Mucosum.

a, This is a very fine membrane, pierced with an infinite number of pores, and moistened by a mucus which is supposed to transude from the surface of the true skin.

b, the colour of the body is found to depend on the colour of the reticulum mucosum; for in negroes it is observed to be perfectly black, whilst the true skin is of the ordinary colour.

c, The blisters which raise the skin when burnt or scalded, are probably occasioned by the rarefaction of this mucus.

Sect. ii. Of the Cutis, or True Skin.

a, The cutis is composed of tendinous fibres closely compacted together, as we may observe in leather, which is the prepared skin of animals. These fibres form a thick cellular network, which every where admits the filaments of nerves, and an infinite number of blood-vessels and lymphatics.

b, The cutis, when the epidermis is taken off, is found to have throughout its whole surface innumerable tendinous papillae, which appear like very minute granulations, and seem to be calculated to receive the impressions of the touch; being the most easily observed where the sense of feeling is the most delicate, as in the palms of the hands, and on the fingers.

c, These papillae which are described as being of a pyramidal figure, are supposed by many anatomical writers to be continuations of the pulpy substance of nerves,

(t) The ingenious Mr Gooch relates the case of a gentleman in Norfolk, who has been frequently attacked by a peculiar kind of fever, which has constantly produced an universal separation of the cuticle from the skin. This separation, which begins to take place within twenty-four hours from the first attack of the fever, is usually completed within ten or twelve days, leaving the skin for sometime exquisitely sensible. The patient has sometimes turned off the cuticle from the wrists to his fingers ends like gloves. One of these cuticular gloves, with an account of the case having been transmitted to the members of the Royal Society, they have given an engraving of it in their transactions. See the Phil. Trans. and Gooch's Med. and Chirurg. Observ.

(u) This was Leuwenhoek's opinion. Ruylich attributed its origin to the nervous papillae of the skin, and Heister thinks it probable that it may owe its formation both to the papillae and the excretory vessels. nerves, whose coats have terminated in the cellular texture of the skin. The great sensibility of these papillae evidently proves them to be exceedingly nervous; but surely the nervous fibrilse of the skin are of themselves scarcely equal to the formation of these papillae; and it seems to be more probable that they are formed like the rest of the cutis.

d. These papillae being described, the uses of the epidermis and the reticulum mucosum will be more easily understood; the latter serving to keep them constantly moist, whilst the former protects them from the external air, and modifies their too great sensibility.

Sect. iii. Of the Glands of the Skin.

a. We meet with two sorts of glands in the skin, viz. the sebaceous, and milky glands.

a. There are certain membranous vesicles, or small cylindrical tubes, continued from the ends of arteries, and discharging a fat and oily humour which serves to lubricate and soften the skin. When this humour is collected and long retained in these tubes, it infilliates; and by enlarging the tubes, gives them the spherical figure which has occasioned them to be called glands; and when the fluid they secrete has acquired a certain degree of thickness, it approaches to the colour and consistence of fat: from this appearance they have derived their name of sebaceous glands.

b. They are found seated in all parts of the body that are under a necessity of being more immediately exposed to the air; as in the face, and wherever the skin is liable to much attrition, as in the arm-pits, groin, &c. and it is the humour they secrete which discolours our linen when we are long without changing it.

a. These glands—which are called milky, from their resembling milk—secrete a fluid similar to milk, placed in all parts of the skin in much greater abundance than the sebaceous glands. Each of these little glands has its excretory duct, which passing through the reticulum mucosum, opens on the surface of the scarf skin, and distills the sweat and matter of insensible perspiration.

b. Besides the excretory vessels which are derived from these glands for the purposes of perspiration, it seems probable that a constant exhalation is carried on from the extremities of the minute arteries which are everywhere dispersed throughout the skin.

a. It will perhaps not be difficult to explain how these processes in the animal economy are conducted. The blood being carried by the circulation to the minute arteries of the cutis, discharges itself of those subtile parts which are capable of passing through the little vessels which open on the surface of the skin. These exhaling vessels are easily demonstrated in the dead subject by throwing water into the arteries; for then small drops exude from all parts of the skin and raise up the cuticle, the pores of which are closed by death; and in the living subject, a looking-glass placed against the skin is soon obscured by the vapour.

b. When the perspiration is by any means increased, and several drops which were insensible when separate, are united together and condensed by the external air, they form upon the skin small but visible drops called sweat. This particularly happens after much exercise; the motion of the blood being then accelerated, and more of it carried to the extremities of the vessels, a greater quantity of the perspirable matter is consequently forced through the passages which are distended to carry it off. So that the skin is found to serve as an emunctory, thro' which the redundant water and sometimes other more saline parts of the blood become unfit for circulation are carried off; but perspiration is not confined to the skin only; a great part of what we are constantly throwing off in this way is from the lungs. The quantity of humour exhaled from the human body by this insensible perspiration is very considerable. Sanctorius (x) an Italian physician, who indefatigably passed a great many years in a series of statical experiments, demonstrated long ago what has been confirmed by later observations; that the quantity of vapour exhaled from the skin, and from the surface of the lungs, amounts nearly to 5-8ths of the aliment we receive. So that if in the warm climate of Italy, a person eats and drinks the quantity of eight pounds in the course of a day, five pounds of it will pass off by insensible perspiration, while three pounds only will be evacuated by stool, urine, the saliva, &c. But in countries where the degree of cold is greater than in Italy, the quantity of perspired matter is less. In some of the more northern climates it is found not to equal the discharge by urine. It is likewise observed to vary according to the season of the year, and according to the constitution, age, sex, diseases, diet, exercise, passions, &c. of different people.

c. From what has been said on this subject, it will be easily conceived that this evacuation cannot be either much increased or diminished in quantity without affecting the health. If it is too copious, the mass of blood is soon deprived of its most subtile parts, and flows with less freedom; the solids being consequently rendered more dry and rigid. And if, on the contrary, the quantity of perspirable matter is diminished, it is either carried off thro' some other channels, or is liable to produce a variety of diseases which will be found to vary according to the season of the year, and the constitution of the body.

d. This perspirable matter and the sweat, for they are both evidently discharged through the same passages, and differ only in quantity, are analogous to the urine; as appears from their taste and saline nature (v). And it is worthy of observation, that when either of these

(x) The insensible perspiration is sometimes distinguished by the name of this physician, who was born in the territories of Venice, and was afterwards a professor in the university of Padua. After estimating the aliment he took in, and the sensible secretions and discharges, he was enabled to ascertain with great accuracy the weight or quantity of insensible perspiration, by means of a statical chair which he contrived for this purpose; and from his experiments, which were conducted with great industry and patience, he was led to determine what kinds of solid or liquid aliment increased or diminished it. From these experiments he formed a system, which he published at Venice in 1644, in the form of aphorisms, under the title of "Ars de Medicina Statica." Baron Haller in his Bibliotheca Anatomica enumerates no less than 27 editions of this work; of which, 19 are of the Latin original, and the others, translations of it into different languages.

(v) Minute crystals have been observed to shoot upon the cloaths of men who work in glass-houses. Haller Fleury. secretions is increased in quantity, the other is diminished; so that they who perspire the least, usually pass the greatest quantity of urine, and vice versa.

Sect. v. Of the Nails.

a, The nails are bodies of a hard and compact nature, resembling horn; formed by a continuation of the papillae of the skin, which enlarging, unite together and gradually harden.

b, The origin of the nails may be easily demonstrated, by gently boiling the hands or feet of the human subject in water; for, by separating the nails from the skin after this process, they will be found adhering to the papillae from which they are produced.

c, The nails increase from their roots, and not from their upper extremity. That part of a nail which is farthest from the root, is the hardest and least sensible. We cut, for instance, the upper end of a nail without exciting any sensation, whilst the most exquisite pain is occasioned by cutting it near its root; that is, near the papillae from which it derives its origin.

d, The nails serve to cover and defend the ends of the fingers from external injury, and are useful to us when we take hold of small and delicate bodies; which without their assistance we should not always be able to accomplish.

Sect. vi. Of the Hair.

a, The hairs, which from their being generally known, do not seem to require any definition; arise from distinct capsules or cartilaginous bulbs seated in the interior part of the skin (z). Some of the bulbs inclose several hairs. They may be observed at the roots of the hairs which form the beard or whiskers of a cat.

b, The hairs, like the nails, grow only from below by a regular proliferation from their root where they receive their nourishment. Their bulbs, when viewed with a microscope (A), are observed to be of an oval shape. The bodies of the hairs, which are the parts without the skin, vary in softness and colour according to the difference of climate, age, or temperament of body (z).

c, In old people the hair usually falls. This event seems to be occasioned by the almost constant dryness which accompanies old age, and gradually hardens all the solid parts of the body. The bulbs of the hair partaking of this change, concrete and become impenetrable to any supply of nourishment. The hairs in consequence of this want of moisture fall out; and if we sometimes see instances of people who preserve their hair at a very advanced age, they are to be attributed to an uncommon degree of humidity in the constitution, which prolongs the suppleness of all the parts. Many people believe that both the hair and the nails grow after death; but this opinion is contradictory to experience.

d, Their general use in the body does not seem to be absolutely determined; but hairs in particular parts, as on the eye-brows and eye-lids, are destined for particular uses, which will be mentioned when those parts are described.

Sect. vii. Of the Membrana Adiposa.

a, This membrane, which is likewise called the cellular (c) or reticular membrane; may be considered as the last of the common integuments; it is everywhere found under the surface of the true skin, and is composed of an infinite number of minute cells united together, and communicating with each other (n). These cells serve as reservoirs to the oily part of the blood, called fat; which is deposited in them by particular vessels, continued from the ends of arteries.

b, The fulness and size of the body are in a great measure proportioned to the quantity of fat contained in these cells; and it seems to be an improper mode of expression to say, that such a one is well in flesh, instead of saying he is fat; for an increase in bulk does not at all add to the size of the flesh, which is made up of the muscles. He who is less disposed to be fat appears to be more muscular; and has indeed commonly stronger and finer muscles than he who is fat.

c, The adeps seems to be renewed by a constant absorption and deposition of it by the vessels destined for that purpose.

Phys.—But this may with as great reason be supposed to proceed from the evaporation of the saline matter used in the composition of glass; as no sort of salt is found to be fixed enough for resisting the violent heat required in glass-making.

(z) Malpighi, and after him the celebrated Ruysch, supposed the hairs to be continuations of nerves; being of opinion that they originated from the papillae of the skin, which are universally allowed to be nervous; and as a corroborating proof of what they advanced, they argued the pain we feel in plucking them out; but later anatomists seem to have rejected this doctrine, and consider the hairs as particular bodies, not arising from the papillae (for in the parts where the papillae abound most there are no hairs) but from bulbs or capsules, which are peculiar to them.

(A) It seems to be much easier to suppose, than to demonstrate, the appearance of the constituent parts of minute bodies like the hairs, which require the assistance of the microscope in examining their anatomical structure. M. Winlow has described the membrane which invests the bulb, and the structure of the bulb itself, as it appears thro' the microscope; but neither the use nor the anatomy of the hair seem to be perfectly understood. The manner in which they are affected in the plica polonica seems to prove them to be pervious thro' their whole length, and they may perhaps serve some useful purposes in perspiration.

(n) The hairs likewise differ from each other, and may not be improperly divided into two classes; one of which may include the hair of the head, chin, pubes, and axilla; and the other, the softer hairs which either have no bulb, or at least a very minute one; and which are to be observed almost everywhere on the surface of the body.

(c) Describing this membrane as a common integument, it seems right to give it the name of membrana adiposa; for under the skin its cells are usually filled with fat; but the same membrane is found to invest the most minute fibres we are able to trace, and is called cellular membrane in some parts of the body where its cells are not filled with fat, and reticular in others, where it appears like very minute net-work.

(d) The two diseases which are peculiar to this membrane, are proofs of this communication; for in the emphysema, all its cells are filled with air; and in the anaemia, they are universally diffused with water. Besides these proofs of this communication from disease, a familiar instance of it may be observed amongst butchers, who usually puncture this membrane, and by inflating it with air add to the good appearance of their meat. that purpose; for without this renewal it would probably become unfit for use. The great waste of it in many diseases, particularly in the consumption, seems to be a sufficient proof that this absorption takes place; and it probably affords considerable nourishment to the body; for in people who have long fasted, the fat has been observed to decrease very fast.

d, The fat is not confined to the skin alone, being met with everywhere in the interstices of muscles, in the omentum, about the kidneys, at the basis of the heart, in the orbits, &c. and some anatomical writers (e) of eminence, have been induced to consider it as the universal connecting medium of every part of the body.

e, The ordinary uses of this oily humour seem to be, to afford moisture to all the parts with which it is connected; to facilitate the action of the muscles; to defend the body from the attrition of external substances; and lastly, to add to its beauty, by making it everywhere smooth and equal.

PART III. OF THE MUSCLES.

CHAP. I. Of the Muscles in General.

a, The muscles are the fleshy parts of the body, and may be considered as the means by which all its movements are performed.

b, They are distinguished by different names (f) which allude to the different dispositions of their fibres, to their situation, or their use. In some, the fibres are placed parallel to each other, in a straight direction, and form what is called a rectilinear muscle; in others, the fibres are placed obliquely with respect to the tendons, like the plume of a pen; these are called penniform muscles; and there are muscles whose fibres cross and intersect each other. There are likewise other distinctions, but to follow them minutely would lead us too far.

c, Anatomists usually distinguish in the generality of muscles, a body, or belly part, and two extremities. The belly of the muscle is composed of an infinite number of fleshy fibres, of a red colour, which every body will understand under the name of flesh. The extremities include the same number of fibres as the belly of the muscle; but they are more firmly united together, and degenerate into a firm, glistering, and inflexible substance, of a white colour, called tendon; if it be round and slender; or aponeurosis, if expanded into a broad flat surface.

d, That extremity which is attached to the most fixed part, has been named the head of the muscle; and that end which is inserted into the moveable part, has been called the tail. But these are arbitrary terms, and custom only can be pleaded for their being retained; for the extremities of a muscle vary with the different situations of the body; and parts that in some motions are fixed, become moveable in others.

e, The muscles are not only surrounded by a very fine membrane, which envelops them separately; but the fibres of every muscle, upon a nice enquiry, are found to be divided into distinct fasciculi or bundles, and these divisions are probably subdivided ad infinitum.

f, Leuwenhoeck fancied he had discovered, by means of his microscope, the ultimate division of a muscle; and that he could point out the simple fibre, which appeared to him to be an hundred times less than a hair; but he was afterwards convinced how much he was mistaken on this subject, and candidly acknowledged, that what he had taken for a simple fibre, was in fact a bundle of fibres.

g, It is easy to observe several of these fasciculi or bundles, in a piece of beef; in which, from the coarseness of its texture, they are very evident.

h, The muscles owe the red colour, which so particularly distinguishes their belly part, to an infinite number of blood-vessels, which are everywhere dispersed like net-work through their whole substance; for their fibres, after having been macerated in water, are, like all other parts of the body deprived of their blood, found to be of a white colour. The blood-vessels are accompanied by nerves, and they are both distributed in such abundance to these parts, that in endeavouring to trace the course of the blood-vessels in a muscle, it would appear to be formed altogether by their ramifications; and in an attempt to follow the branches of its nerve, their number and minuteness would soon exclude the eye and the knife of the anatomist; and the whole muscle would appear perhaps as if composed only of nerves.

i, We defined the muscles to be moving powers, and we are all sensible of the propriety of this definition; but nobody seems to understand perfectly how these powers are effected.

k, If a muscle is pricked or irritated, it contracts, and becomes firm and rigid. This is called its tonic action, or irritable principle.

l, If it is much distended or compressed, it endeavours to re-establish itself by its spring, like all elastic bodies.

m, But besides these two properties, it possesses a third, which is peculiar to it; and this is, that without having been either pricked or irritated, drawn out or distended, it shortens itself, or at least endeavours to shorten itself, at the command of the will. There are some muscles, however, which are called involuntary; because they act independent of the will, as the heart and muscles of respiration. The last of these may be said to have a mixed motion, being in some measure influenced by the will.

n, It is this action of the voluntary muscles which is called muscular motion; and of which we will endeavour to convey an idea in a few words. To illu-

(f) Haller. (f) Different authors have described the same muscle by different names. Many new Latin ones have lately been introduced by the celebrated Albion with great seeming propriety; but such alterations are liable to create confusion. In France, Mr. Winiford's method is universally followed, who distinguished all the muscles by French names, which are often very different from any Latin name before in use. All these variations are pointed out in the later editions of Douglas's Myography. illustrate what we shall advance, it will be necessary to take a muscle or two as examples.

In the osteological part of the work, the generality of the bones were described as being articulated to each other with so much art, as to be capable of motion every way; but their motions cannot be performed by themselves, as they are perfectly passive in all the movements of the body. The muscles are a kind of cords attached to the bones, which they move in different directions by shortening their fibres. Every one is acquainted with the motion of the lower jaw: we are able first to lower it, and then to raise and apply it strongly against the upper jaw. The action of the masseter muscles, in this case is very sensible above. It is fixed to the os maxillae, and part of the upper jaw; and below, it is attached to the lower and outer ridge of the under jaw. When we are willing then to raise the jaw, its muscles are put into action. The masseter on each side contracts; its fleshy part swells and enlarges, and becomes harder and shorter; and as the upper end of this muscle is attached to a fixed and immovable part, which is the case with the maxilla superior, the lower extremity is necessarily drawn towards the upper one, bringing with it the lower jaw. This muscle, when in action, may be easily felt, by applying the hand to the cheek, between the cheek bone and the lower jaw.

Again, when we desire to bend the finger, the flexor muscles which are attached to the os humeri, and the bones of the forearm, and have their moveable part fixed to the inner extremities of the fingers, contract and shorten themselves; and thus the ends of the fingers are drawn towards the palm of the hand.

It will here naturally be inquired by what mechanism this power to contract is occasioned. Many opinions have been formed, and much has been written on this subject. Some of these systems were the result of much industry and ingenuity, and required no small share of mathematical knowledge not only to invent, but to understand them. Some have undertaken to explain the cause of contraction, by supposing that every muscular fibre forms as it were a chain of very minute bladders; while the nerves which are distributed through the muscle bring with them a supply of animal spirits, which at our will fill these bladders, and by increasing their diameter in width, shorten them, and of course the whole fibre. We will dwell no longer on this ingenious hypothesis, or say anything of other systems, which as well as that we have mentioned, are far from being satisfactory; and we will only observe, that here, as in many other of her works, Nature seems to have drawn a boundary to our inquiries, beyond which no human penetration will probably ever extend.

Some few things we know with certainty on this subject, and these are, that the nerves are essentially necessary to muscular motion; for if we tie up or divide the nerves leading to any muscle, that muscle becomes paralytic and incapable of action; that the cause of palsy is usually not seated in the part affected, but commonly in the nerve leading to that part, and perhaps in the brain or spinal marrow, from whence the nerves originate; and that a ligature made on the artery leading to a muscle produces the same effects as a ligature on the nerve, by rendering it inactive, and even insensible; and this last observation seems to prove, that a regular supply of blood, if not the immediate cause of muscular motion, is at least essentially necessary to it.

As the enumeration and description of the particular muscles must be dry and unentertaining to the generality of readers, yet cannot be omitted in a work of this nature, it appeared eligible to throw this part of the subject into the form of a table, leaving the reader to examine or pass it over as he inclines. ### Parts of the Body

#### Names of the Muscles

| Parts of the Body | Names of the Muscles | |-------------------|----------------------| | Integuments of the cranium. Ear-external. | 1. Occipito-frontalis. Corrugator supercilii. | | | 2. Auricularis auris. Anterior auris. | | | 3. Retroauriculares auris. Helix major. Helix minor. | | | 4. Tragus. Antitragus. | | | 5. Trapezium auris. Longus tympani. | | | 6. Tensor tympani. Stapedius. | | | 7. Oticus communis palpebrarum. Levator palpebrae superioris. | | | 8. Levator palpebrae inferioris. Depressor oculi. Adductor oculi. | | | 9. Obliquus inferior, ductus lacrimalis. Obliquus inferior. Compressor naris. | | | 10. Levator anguli oris. Levator labii superioris alaeque nasi. | | | 11. Depressor anguli oris. Levator labii inferioris. Levator labii inferioris. | | | 12. Buccinator. Zygomaticus major. Zygomaticus minor. Orbicularis oris. | | Lower-jaw. | 1. Temporalis. Masseter. | | | 2. Pterygoides internus. Pterygoides externus. | | Anterior part of the neck. | 1. Platysma myoides. Sterno-clavicularis. | | Between the lower-jaw and os hyoides. | 2. Digastricus. Mylo-hyoides. Genio-hyoides. | | Between the os hyoides and trunk. | 3. Genio-hyoides. Hyo-hyoides. | | Between the lower-jaw and os hyoides laterally. | 4. Digastricus. Sterno-hyoides. Omo-hyoides. | | Entry into the fauces. About the glottis, and behind the larynx. | 5. Stylo-hyoides. Stylo-pharyngeus. Circumvallate, or Tonsor palati. | | Posterior part of the pharynx. | 6. Levator palati. Constrictor pharyngis superior. Palato-pharyngeus. | | | 7. Aryepiglotticus. Aryepiglotticus posterior. Aryepiglotticus lateralis. Aryepiglotticus superior. | | | 8. Aryepiglotticus transversus. Thyro-epiglotticus. Aryepiglotticus inferior. |

#### Origin

Ridge near the middle of the os occipitis.

Internal angular process of the os frontis, above the joining of the os naso with the superior maxillary.

Tendon of the occipito-frontalis where it covers the aponeurosis of the temporal muscle.

Posterior part of the zygoma.

Two or three small muscles from the mastoid process.

Upper part of the helix.

Inferior part of the helix.

Middle and outer part of the concha.

Internal part of the cartilage supporting the antitragus.

Prominent part of the concha.

Spinous process of the os sphenoides.

Extremity of the eustachian tube, and spinous process of the os sphenoides.

A little cavern in the pars petrota near the mastoid process.

Orbital process of the superior maxillary bone.

Foramen opticum of the os sphenoides.

Foramen opticum.

Inferior part of the foramen opticum.

Between the obliquus superior and depressor.

Bony partition between the foramen opticum and lacrimum.

Edge of the foramen opticum.

Orbital process of the superior maxillary bone.

Root of the ala naso externally.

Hollow of the superior maxillary bone, between the root of the socket of the first dens molaris and the foramen infratemporalis.

Two portions. 1. Orbital process; 2. Nasal process of the superior maxillary bone.

Os maxillare superius.

Lower edge of the maxilla inferior.

Inferior part of the lower jaw.

Lower jaw, at the root of the dens caninus and two dentes incisoris.

Lower jaw, as far back as the last dens molaris.

Os male near the zygomatic future.

Upper part of the os male.

Formed by the muscles that move the lips.

Semicircular ridge of the parietal bone.

Superior maxillary bone.

Upper and internal part of the pterygoid process.

Outside of the pterygoid, and root of the temporal process of the sphenoid bone from the adjacent tubercle of the os maxillare.

Cellular substance covering the upper parts of the deltoid and pectoral muscles.

By two portions. 1. The top of the sternum. 2. The upper and anterior part of the clavicle.

Root of the mastoid process of the temporal bone.

All the inside of the lower jaw.

Internal protuberance in the middle of the lower jaw.

The same with the former.

Base, cornu, and appendix of the os hyoides.

Root of the tongue laterally.

Cartilaginous extremity of the first rib.

Superior cornu of the scapula.

Whole edge of the uppermost bone of the sternum internally.

Part of the basis and almost all the cornu of the os hyoides.

Side and fore part of the cricoid cartilage.

Styloid process, and a ligament connecting it with the lower jaw.

Middle and inferior part of the styloid process.

Root of the styloid process.

Spinous process of the os sphenoides, and eustachian tube.

Extremity of the pars petrota of the temporal bone, and membranous part of the eustachian tube.

Side of the tongue, near its root.

Middle of the velum pendulum palati.

Extremity of the future joining the palate bones.

Back part of the cricoid cartilage.

Cricoid cartilage, laterally, where it is covered by the thyroid.

Base of one arytenoid cartilage, and crosses its fellow.

Side of one arytenoid cartilage, its fibres running across.

Posterior part of the thyroid cartilage laterally.

Near the former.

Lateral and upper part of the arytenoid cartilage.

Concealed process of the os occipitis; pterygoid process of the os sphenoides, and from the upper jaw.

Appendix of the os hyoides, the cornu of the bone, and the ligament connecting it to the thyroid.

Side of the thyroid cartilage, and from the cricoid cartilage. | Parts of the Body | Names of the Muscles | |------------------|----------------------| | Anterior part of the abdomen | 1. Obliquus descendens externus. 2. Obliquus descendens internus. 3. Transversalis. 4. Rectus abdominis. | | Male organs of generation | 5. Pyramidalis. 6. Darts. 7. Cremaster. 8. Erector penis. 9. Accelerator urinae, seu ejaculator femoris. | | Anus | 10. Transversalis penis. 11. Sphincter ani. 12. Levator ani. 13. Erector clitoridis. 14. Sphincter vaginae. 15. Transversus perinei. 16. Sphincter ani. 17. Levator ani. 18. Erector internus. 19. Transversus, or greater muscle of the diaphragm. 20. Inferior, or lesser muscle of the diaphragm. 21. Quadratus lumborum. 22. Psoas parvus. 23. Psoas major. | | Female organs of generation | 24. Iliacus internus. 25. Psoas major. 26. Subclavius. 27. Pectoralis minor. 28. Serratus magnus. 29. Intercostales externi. 30. Intercostales interni. 31. Triangularis, or Scapulo-costalis. | | Within the pelvis | 32. Longus colli. 33. Rectus capitis internus major. 34. Rectus capitis internus minor. 35. Rectus capitis lateralis. 36. Trapezius seu cucullaris. 37. Latissimus dorsi. 38. Serratus posterior inferior. 39. Rhomboides. 40. Splenius. 41. Splenius. 42. Splenius. 43. Splenius. 44. Splenius. 45. Splenius. 46. Splenius. 47. Splenius. 48. Splenius. 49. Splenius. 50. Complexus. 51. Trapezius-massilis. 52. Levator scapulae. 53. Semispinalis dorsi. 54. Multifidus spinae. 55. Semispinalis colli. 56. Rectus capitis posterior major. 57. Rectus capitis posterior minor. 58. Obliquus capitis superior. 59. Obliquus capitis inferior. 60. Scalene anticus. 61. Scalene medius. 62. Scalene posterior. |

Eight of the inferior ribs. Spine of the os ilium, the tendon of the latissimus dorsi. Transverse processes of the last vertebra of the spine of the os ilium internally, by two heads, from the fore and upper parts together. Along with the rectus. Cremaster muscle. Obliquus internus. Tuberosity of the os ilium. Sphincter ani, membranous part of the urotheca. Membrane covering the tuberosity of the skin and fat surrounding the anus. Os pubis, or ilium, and tendinous nerve. Crus of the os ilium. Sphincter ani, and posterior side of the vescica. Cellular membrane covering the os ilium. As in the male. As in the female. Os ilium, ilium, and internal crista iliaca. Spinous process of the os ilium. Cartilago coniformis, cartilages of the lower end of the ilium. Inferior part of the middle tendon. Posterior part of the spine and thoracic sides of the two upper vertebrae. Side of the body, and transverse process of all those of the ilium. Spine, and edge of the os ilium. Cartilaginous extremities of the bony and fibrous half the inferior part of the ileum. Clavicle. Coracoid process of the scapula. Base of the scapula internally. Inferior acute edge of each upper rib. In the same manner as the foramen. Cartilago coniformis, and edge of the lower end of the ilium.

Three superior vertebrae of thick lateral processes, and fifth vertebrae of the lumbar region. Transverse processes of the fourth vertebra. Fore part of the body of the vertebra. Point of the transverse process of the first lumbar vertebra. Protuberance in the middle of the os ilium, towards the mamillo process, terminating in the neck, and from all those of the ilium. Posterior part of the os ilium, at its junction with the inferior ones of the vertebral column. Spinous processes of the two inferior vertebrae. From the spinous process of the third to the three inferior vertebrae of the ilium. Four superior spinous processes.

Spinous processes of the two inferior vertebrae. Spinous processes of the two middle vertebrae, and all the spinous process of the os ilium, proceeding in common with the longitibialis. Transverse processes of the fifth vertebra. Transverse processes of the uppermost lumbar vertebrae. Transverse processes of the lowermost lumbar vertebrae. Transverse processes of the seventh lumbar vertebrae. Transverse processes of the eighth lumbar vertebrae. Transverse processes of the ninth lumbar vertebrae. Transverse processes of the tenth lumbar vertebrae. External part of the spinous process of the os ilium. Protuberance in the middle back part. Transverse processes of the fibula of the fourth, fifth, sixth, and seventh lumbar vertebrae. All the transverse processes of the vertebrae. Fifth and sixth transverse processes of the ilium. ### A TABLE OF THE MUSCLES.

#### INSERTION.

| Muscle | Insertion | |--------|-----------| | Tibialis anterior | Inferior part of the tubercle of the tibia, and the upper part of its spine. | | Tibialis posterior | Tibia, near the fibularis. | | Vastus lateralis | Upper part of the patella; and from the inferior part of this bone the tendon is sent off of the tibia. | | Vastus medialis | A large share of the upper part of the patella. | | Vastus intermedius | Upper and inside of the patella. | | Gracilis | Upper part of the patella. | | Sartorius | Inside of the ridge of the tibia, a little below its tubercle. | | Semitendinosus | Superior and back part of the head of the tibia. | | Semimembranosus | Upper part of the head of the fibula. | | Popliteus | Ridge at the upper and internal edge of the tibia. | | Gastrocnemius | Upper and posterior part of the os calcis, by the tendo Achillis. | | Soleus | Inside of the posterior part of the os calcis. | | Flexor hallucis longus | Inside of the os cuneiforme internum, and posterior end of the metatarsal bone sustaining Os naviculare, cuneiforme internum and medium; os calcis, cuboides, and the root of the bone sustaining the middle toe. | | Flexor digitorum longus | Outer side of the root of the metatarsal bone sustaining the great toe, and os cuneiforme. | | Extensor hallucis longus | Root and external part of the metatarsal bone sustaining the little toe. | | Extensor digitorum longus | Root of the first joint of each of the small toes, and expanded over their upper side as far as the second phalanx of the four lesser toes. | | Tibialis anterior | Tendinous expansion covering the small toes, and that covering the upper part of the second phalanx of the four lesser toes. | | Tibialis posterior | Extremity of the last joint of the four lesser toes. | | Tibialis anterior | Tendon of the flexor longus. | | Tibialis posterior | Inside of the first joint of the four lesser toes. | | Vastus lateralis | Posterior part of the first and last joint of the great toe. | | Vastus medialis | Last joint of the great toe. | | Gracilis | External os sesamoidae, and root of the first joint of the great toe. | | Sartorius | The same with the former. | | Semitendinosus | External os sesamoidae, and root of the metatarsal bone of the great toe. | | Semimembranosus | Root of the first joint of the little toe externally. | | Popliteus | Anterior extremity of the metatarsal bone, and root of the first joint of the little toe. | | Gastrocnemius | Inside of the root of the first joint of the fore toe. | | Soleus | Outside of the root of the first joint of the fore toe. | | Flexor hallucis longus | Outside of the root of the first joint of the second toe. | | Flexor digitorum longus | Outside of the root of the first joint of the third toe. | | Extensor hallucis longus | Inside of the root of the first joint of the middle toe. | | Extensor digitorum longus | Root of the first joint of the third toe. | | Tibialis anterior | Root of the first joint of the little toe. | | Tibialis posterior | Outside of the anterior extremity of the metatarsal bone of the little toe. | | Part | Uses | |----------------------------------------------------------------------|---------------------------------------------------------------------| | Orbicularis palpebra | To move the leg obliquely inwards, or to bring one leg and thigh cross the other. | | Inner part of the os hyoid | To bend the thigh and leg inwards. | | Upper part of the helix | To extend the leg by means of the patella, like a pulley. | | Eminence of the helix | To extend the leg. | | Back-ear, opposite to the helix | To extend the leg. | | Cartilage of the helix | To assist in the extension of the leg. | | Crus of the helix | To bend the leg backwards and a little inwards. | | Point of the tragus | To bend the leg and bring it directly backwards. | | Tip of the antitragus | To bend the leg. | | Opposite to the mouth | To move the leg obliquely outwards, and to assist in bending it. | | Long process of the helix | To extend the foot. | | Small process of the helix | To assist the former. | | Posterior part of the helix | To bend the foot. | | Nasal process of the helix | To bring the foot inwards and upwards. | | Cartilage called larynx | To move the foot outwards, and bend it a little. | | Upper and fore part of the great toe | To pull the foot outwards and upwards. | | Opposite to the formic metatarsal | To extend all the joints of the four small toes. | | Opposite to the inner side of the eye | To extend the toes. | | Globe of the eye, oculum | To bend the second joint of the toes. | | Tunica fibrosa | To bend the toes. | | Tunica fibrosa, the last joint | To assist in bending the toes. | | Anterior extremity | To extend the toes. | | Angle of the mouth, great toe | To bend this first joint. | | Upper lip, and root | To pull the great toe from the rest. | | Angle of the mouth | To bring this toe nearer the rest. | | Angle of the lower lip and skin | To draw the little toe outwards. | | Angle of the mouth | To bend the little toe. | | Angle of the lower lip and skin | To pull the fore toe inwards. | | Coronoid process of the mandible | To pull the fore toe outwards towards the rest. | | Angle of the lower lip and skin | To pull the second toe outwards. | | Angle of the lower lip and skin | To pull the third toe outwards. | | Condylar process of the mandible | To pull the middle toe inwards. | | Lower jaw, between massoids | To pull the third toe inwards. | | Massoid process | To pull the little toe inwards. | | Anterior part of the tongue | To bring the little toe towards the great one. | | Lower edge of the tongue | Middle of the velum | | Tip, middle, and side of the tongue | Edge of the upper | | Tip of the tongue | Tip of the uvula | | Base of the os hyoid | Posterior part of the base | | Base of the os hyoid | Side of the base of the other | | Rough line at the side of the tongue | Arytenoid cartilage | | Rough line opposite to the two portions | Epiglottis, along | | Root of the tongue | White line in the | | Os hyoides at the side of the pharynx | Middle of the cur | | Velum pendulum | White line in the | EXPLANATION OF PLATE XV. AND XVI.

PLATE XV.

Fig. 1. The Muscles immediately under the common teguments on the anterior part of the body, are represented on the right side; and on the left side the Muscles are seen which come in view when the exterior ones are taken away.

A, The frontal muscle. B, The tendinous aponeurosis which joins it to the occipital; hence both named occipito-frontalis. C, Attollens aureum. D, The ear. E, Anterior auris. F F, Orbicularis palpebrarum. G, Levator labii superioris alaeque nasi. H, Levator anguli oris. I, Zygomaticus minor. K, Zygomaticus major. L, Masseter. M, Orbicularis oris. N, Depressor labii inferioris. O, Depressor anguli oris. P, Buccinator. Q Q, Platysma myoides. R R, Sterno-cleido-mastoideus. S, Part of the trapezius. T, Part of the scaleni.

SUPERIOR EXTREMITY.—U, Deltoideus. V, Pectoralis major. W, Part of the latissimus dorsi. X X, Biceps flexor cubiti. Y Y, Part of the brachialis externus. Z Z, The beginning of the tendinous aponeurosis (from the biceps) which is spread over the muscles of the fore-arm. a a, Its strong tendon inserted into the tubercle of the radius. b b, Part of the brachialis internus. c, Pronator radii teres. d, Flexor carpi radialis. e, Part of the flexor carpi ulnaris. f, Palmaris longus. g, Aponeurosis palmaris. 3, Palmaris brevis. i, Ligamentum carpi annulare. 2 2, Abductor minimi digiti. h, Supinator radii longus. i, The tendons of the thumb. k, Abductor pollicis. l, Flexor pollicis longus. m m, The tendons of the flexor sublimis perforatus, profundus perforans, and lumbricales.—The sheaths are entire in the right hand, —in the left cut open, to show the tendons of the flexor profundus perforating the sublimis.

Muscles not referred to—in the left superior extremity.—n, Pectoralis minor, seu serratus anticus minor. o, The two heads of (x x) the biceps. p, Coracobrachialis. q q, The long head of the triceps extensor cubiti. r r, Teres major. ff, Subclapularis. t t, Extensor radiales. u, Supinator brevis. v, The cut extremity of the pronator teres. w, Flexor sublimis perforatus. x, Part of the flexor profundus. y, Flexor pollicis longus. z, Part of the flexor pollicis brevis. 4, Abductor minimi digiti. 5, The four lumbricales.

TRUNK.—6, Serrated extremities of the serratus anticus major. 7 7, Obliquus externus abdominis. 8 8, The linea alba. 9, The umbilicus. 10, Pyramidalis. 11 11, The spermatic cord. On the left side, it is covered by the cremaster. 12 12, Rectus abdominis. 13, Obliquus internus. 14 14, &c. Intercostal muscles.

INFERIOR EXTREMITIES.—a a, The gracilis. b b, Parts of the triceps. c c, Pectilis. d d, Ploas magnus. e e, Iliacus internus. f, Part of the gluteus medius. g, Part of the gluteus minimus. h, Cut extremity of the rectus cruris. i i, Valtus externus. k, Tendon of the rectus cruris. ll, Valtus internus. * Sartorius muscle. ** Fleshly origin of the tenor vaginae femoris or membranofus. Its tendinous aponeurosis covers (i), the vastus externus in the right-side. m m, Patella. n n, Ligament or tendon from it to the tibia. o, Rectus cruris. p, Cruræus. q q, The tibia. r r, Part of the gemellus or gastrocnemius externus. f f, Part of the soleus or gastrocnemius internus. t, Tibialis anticus. u, Tibialis pollicis. v v, Peronæi muscles. w w, Extensor longus digitorum pedis. x x, Extensor longus pollicis pedis. y, Abductor pollicis pedis.

Fig. 2. The Muscles, Glands, &c. of the left side of the face and neck, after the common tegments and platysma myoides have been taken off.

a, The frontal muscle. b, Temporalis and temporal artery. c, Orbicularis palpebrarum. d, Levator labii superioris alaeque nasi. e, Levator anguli oris. f, Zygomaticus. g, Depressor labii inferioris. h, Depressor anguli oris. i, Buccinator. k, Masseter. l l, Parotid gland. m, Its duct. n, Sterno-cleido-mastoideus. o, Part of the trapezius. p, Sterno-hyoideus. q, Sterno-thyroidæus. r, Omo-hyoideus. s, Levator scapulae. t t, Scaleni. u, Part of the splenius.

Fig. 3. The Muscles of the face and neck, in view after the exterior ones are taken away.

a a, Corrugator supercilii. b, Temporalis. c, Tendon of the levator palpebrae superioris. d, Tendon of the orbicularis palpebrarum. e, Masseter. f, Buccinator. g, Levator anguli oris. h, Depressor labii superioris alaeque nasi. i, Orbicularis oris. k, Depressor anguli oris. l, Muscles of the os hyoides. m, Sterno-cleido-mastoideus.

Fig. 4. Some of the Muscles of the os hyoides, and submaxillary gland.

a, Part of the masseter muscle. b, Posterior head of the digastric. c, Its anterior head. d d, Sterno-hyoideus. e, Omo-hyoideus. f, Stylo-hyoideus. g, Submaxillary gland in situ.

Fig. 5. The submaxillary gland and duct.

a, Musculus mylo-hyoideus. b, Hyo-glossus. c, submaxillary gland extra fitu. d, Its duct.

PLATE XVI.

Fig. 1. The Muscles immediately under the common tegments on the posterior part of the body are represented in the right side; and on the left side the Muscles are seen which come in view when the exterior ones are taken away.

HEAD—A A, Occipito-frontalis. B, Attolens aureum. C, Part of the orbicularis palpebrarum. D, Masseter. E, Pterygoidæus internus.

TRUNK.—Right side. F F F, Trapezius seu cucullaris. G G G G, Latissimus dorsi. H, Part of the obliquus externus abdominis.

TRUNK.—Left side. I, Splenius. K, Part of the complexus. L, Levator scapulae. M, Rhomboideus. N N, Serratus posticus inferior. O, Part of the longissimus dorsi. P, Part of the facro-lumbalis. Q, Part of the semi-spinalis dorsi. R, Part of the serratus anticus major. S, Part of the obliquus internus abdominis.

SUPERIOR EXTREMITY.—Right side. T, Deltoideus. Z z PART IV. OF THE ABDOMEN, OR LOWER BELLY.

a, The abdomen, or lower belly, extends from the lower extremity of the sternum, or the hollow usually called the pit of the stomach, and more properly scorbicularis cordis, to the lower part of the trunk.

b, It is distinguished into three divisions, called regions: of these the superior one, which is called the epigastric region, begins immediately under the sternum, and extends to within two fingers' breadth of the navel, where the middle or umbilical region begins, and reaches to the same distance below the navel. The third, which is called the hypogastric, includes the rest of the abdomen, as far as the os pubis.

c, Each of these regions is subdivided into three parts; two of which compose the sides, and the other the middle part of each region.

d, The middle part of the upper region is called epigastrium; and its two sides hypochondria. The middle part of the next region is the umbilical region, properly so called, (o) and its two sides are the flanks, or iliac regions. Lastly, the middle part of the lower region retains the name of hypogastrium, and its sides are called inguina or groin. The back part of the abdomen bears the name of lumbar region.

e, These are the divisions of the lower belly, which are necessary to be held in remembrance as they frequently occur in chirurgical and anatomical writing. We will now proceed to examine the contents of the abdomen, and after having pointed out the name and arrangement of the several viscera contained in it, describe each of them separately.

f, After having removed the skin, adipose membrane, and abdominal muscles, of which there are five on each side, we discover the peritoneum; for so the membrane is called which envelops all the viscera of the lower belly. This being opened, the first part that presents itself is the omentum or cawl, floating on the surface of the intestines; which are likewise seen everywhere loose and moist, and making a great number of circumvolutions through the whole cavity of the abdomen. The stomach is placed in the epigastrium, and under the stomach is the pancreas. The liver fills the right hypochondrium, and the spleen is situated in the left. The kidneys are seen about the middle of the lumbar region, and the urinary bladder and parts of generation are seated in the lower division of the belly.

CHAP. I.

Of the Peritoneum.

a, The peritoneum is a strong, simple membrane, by which all the viscera of the abdomen are surrounded, and in some measure supported. Many anatomical writers have described it as being composed of two distinct membranous laminae; but their descriptions seem to be erroneous. What perhaps appeared to be a second lamina, being found to be simply a cellular coat; which tends off productions to the blood vessels passing out.

(o) The navel is formed by the extremities of the vessels which keep up a communication between the mother and the fetus in utero. As soon as the child comes into the world, these vessels are divided and secured by ligature, their cavities disappear, and in progress of time they become a ligamentous cord. out of the abdominal cavity. The aorta, and vena cava, likewise, derive a covering from the same membrane; which seems to be a part of the cellular membrane we have already described.

b, The peritoneum, by its productions and duplications, envelops the greatest part of the abdominal viscera. It is soft, and capable of considerable extension, and is kept smooth and moist by a vapour which is constantly exhaling from its inner surface, and is returned again into the circulation by the absorbents.

c, This moisture not only contributes to the softness of the peritoneum, but prevents the attrition, and other ill effects which would otherwise probably be occasioned by the motion of the viscera upon each other.

d, When this fluid is supplied in too great a quantity, or the absorbents become incapable of carrying it off, it accumulates; and constitutes an ascites or dropy of the belly; and when by any means the exhalation is discontinued, the peritoneum thickens; becomes diseased; and the viscera are sometimes found adhering to each other.

e, It is supplied with blood by branches of the mammary, epigastric, and phrenic arteries; and the blood is carried back by veins of the same name. Its nerves are derived from the spinal marrow of the lumbar vertebrae, and os sacrum; being branches of the nerves distributed to the abdominal muscles, and it likewise receives some branches from the nerves which go to the diaphragm.

C H A P. II.

Of the Omentum.

a, The omentum or cawl is a most delicate double membrane, interlarded with a great deal of fat, which is attached to the stomach, spleen, duodenum, and colon; and from thence hangs down loose and floating on the surface of the intestines. Sometimes it descends as low as the groin, and in people who are subject to ruptures, it is now and then found to pass through the abdominal rings, and defend the hernial sac. The disease is then called epiplocele, for the Greeks gave the name of epiploon, to this viscus. The omentum, by being double, forms a kind of pouch open only at one end, and some French writers have on this account compared it to a cul de sac. The celebrated M. Winckel has demonstrated this aperture, which is situated under the great lobe of the liver near the beginning of the lesser lobe; and the whole pouch may be distended by blowing air in at this opening (n).

b, The celiac and mesenteric arteries send off branches to the omentum, and its redundant blood passes into the branches of the vena porta.

c, The use of this viscus is not perfectly known. It has been supposed, with great appearance of probability, to contribute to the warmth and moisture of the other viscera; for adhesions have been observed to have taken place where the fat of the omentum has been much wasted. But there are authors who consider it as assailing in the preparation of bile; and Malpighi has remarked, that in warming the part which in frogs supplies the place of omentum, the fat was seen to dissolve into spherical drops, which passed into the vena porta.

C H A P. III.

Of the Stomach.

a, The stomach is a membranous and muscular bag, in shape not unlike a bag-pipe, lying across the upper part of the abdomen, and inclining rather more to the left than the right side.

b, It has two orifices, one of which receives the end of the esophagus, and is called the cardia; and sometimes the left and upper orifice of the stomach; though its situation is not much higher than the other, which is called the right and inferior orifice, and more commonly the pylorus; both these openings are more elevated than the body of the stomach.

c, The aliment passes down the esophagus into the stomach through the cardia, and after having undergone the necessary digestion, passes out at the pylorus where the intestinal canal commences.

d, The stomach is composed of four tunics or coats, which are so intimately connected together, that it requires no little dexterity in the anatomist to demonstrate them. The exterior one is membranous, being derived from the peritoneum. The second is a muscular tunic, composed of fleshy fibres which are in the greatest number about the two orifices. The third is called the nervous coat, and within this is the villous or velvet-like coat, which composes the inside of the stomach.

e, The two last coats being more extensive than the two first, form the folds which are observed everywhere in the cavity of this viscus; and more particularly about the pylorus, where they seem to impede the two hasty exclusion of the aliment, making a considerable plait, called valvula pylori.

f, The inner coat is constantly moistened by a mucus which approaches to the nature of the saliva, and is called the gastric juice; this liquor is supposed to be secreted by certain minute glands (1) seated in the nervous tunic, whose excretory ducts open on the surface of the villous coat.

g, The arteries of the stomach called the gastric arteries, are derived from the celiac; some of its veins pass to the splenic, and others to the vena porta; and its nerves are chiefly from the eighth pair or par vagum.

h, The account given of the tunics of the stomach may be applied to the whole alimentary canal; for both the esophagus and intestines are, like this viscus, composed of four coats.

i, Before we describe the course of the aliment and the uses of the stomach, it will be necessary to speak of other parts which assist in the process of digestion.

C H A P. IV.

Of the Oesophagus.

a, The esophagus or gullet, is a membranous and muscular canal extending from the bottom of the mouth to

(n) This membranous bag, though exceedingly thin and transparent, is found capable of supporting mercury thrown into it by the same channel.

(1) Heffer speaking of these glands very properly says, "in porcis facile, in homine raro observantur," for although many anatomical writers have described their appearance and figure, yet they do not seem to have been hitherto satisfactorily demonstrated in the human stomach. to the upper orifice of the stomach. Its upper part where the aliment is received, is shaped somewhat like a funnel, and is called the pharynx.

b, From hence it passes down close to the bodies of the vertebrae as far as the diaphragm, where there is an opening through which it passes; and then terminates in the stomach about the eleventh or twelfth vertebra of the back.

c, The oesophagus is supplied with blood vessels from the carotid arteries, and from the aorta; and receives other branches from the intercostal and celiac arteries. The blood is returned from these vessels into the jugular veins, and the axillary.

d, Its nerves are derived from the eighth pair.

e, We likewise meet with a mucous in the oesophagus which every where lubricates its inner surface, and tends to assist in deglutition. This mucous seems to be secreted by very minute glands, like the mucus in other parts of the alimentary canal.

CHAP. V. Of the Intestines.

a, The intestines form a canal which is usually six times longer than the body to which it belongs. This canal extends from the pylorus or inferior orifice of the stomach, to the anus.

b, It will be easily understood, that a part of so great length must necessarily make many circumvolutions to be confined with so many other viscera in the capacity of the lower belly.

c, Although the intestines are in fact, as we have observed, only one long and extensive canal; yet different parts have been distinguished by different names.

d, The intestines are first distinguished into two parts, one of which begins at the stomach and is called the thin or small intestine, from the small size of the canal, and the thickness of its coats when compared with the other part, which is called the large intestine; and includes the lower portion of the canal down to the anus.

e, Each of these parts has its subdivisions. The small intestines being distinguished into duodenum, jejunum, and ileum; and the larger portion into cæcum, colon, and rectum.

f, The small intestines fill the middle and fore-parts of the belly, while the large intestines fill the sides and both the upper and lower parts of the cavity.

g, The duodenum, which is the first of the small intestines, is so called, because it is about twelve inches long. It begins at the pylorus, and terminates in the jejunum; which is a part of the canal observed to be usually more empty than the other intestines; this appearance gives it its name, and likewise serves to point out where it begins.

h, The next division is the ileum, which of itself exceeds the united length of the duodenum and jejunum; and has received its name from its situation in the lower part of the umbilical region, near the os innominata. The large circumvolution of the ileum covers the first of the large intestines called the cæcum, which seems properly to belong to the colon; being a kind of pouch about as wide as four fingers, and nearly of the same length; having exteriorly a little appendix, called appendix cæci.

i, The cæcum is placed in the cavity of the os ilium on the right side, and terminates in the colon, which is the largest of all the intestines.

k, This intestine ascends by the right kidney to which it is attached, passes under the hollow part of the liver, and the bottom of the stomach to the spleen to which it is likewise secured, as it is also to the left kidney; and from hence passes down towards the os sacrum, where from its straight course the canal begins to take the name of rectum.

l, There are three ligamentous bands extending throughout the whole length of the colon, which by being shorter than its two inner coats, serve to increase the plaiting on the inner surface of this gut.

m, The anus which terminates the intestinum rectum, is furnished with three muscles; one of these is composed of circular fibres, and from its use in shutting the passage of the anus, is called sphincter ani.

n, The other two are the levatores ani; so called, because they elevate the anus after defecation. When these by palsy, or any other disease, lose the power of contracting, the anus prolapses; and when the sphincter is affected by similar causes, the faeces are voided involuntarily.

o, It has already been observed, that the intestinal canal is composed of four tunics; but it remains to be remarked, that here, as in the stomach, the two inner tunics being more extensive than the other two, form the plaiting which are to be seen in the inner surface of the intestines, and are called valvulae conniventes.

p, Some authors have considered these plaitings as tending to retard the motion of the faeces, so as to afford more time for the separation of the chyle; but there are others who attribute to them a different use: They contend that these valves, by being naturally inclined downwards, cannot impede the descent of the faeces; but that they are intended to prevent their return upwards.

q, They are probably destined for both these uses; for although these folds incline to their lower side, yet the inequalities they occasion in the canal are sufficient to retard in some measure the progressive motion of the faeces, and to afford a greater surface for the absorption of chyle; and their natural position seems to oppose itself to the return of the aliment.

r, Besides the valvulae conniventes, there is one more considerable than the rest, called the valve of the colon; which is found at that part of the canal where the intestinum ileum is joined to the colon. This valve permits the alimentary pulp to pass downwards, but serves to prevent its return upwards; and it is by this valve that glisters are prevented from passing into the small intestines (x).

s, Of the little vermiform appendix of the cæcum, it will be sufficient to say that its uses have never yet been ascertained. In birds we meet with two of these appendages.

t, The intestines are lubricated by a constant supply of mucus, formerly believed to be secreted by very minute glands, but now generally supposed to be exhaled from

(x) This, however, is not invariably the case; for the contents of a glistery have been found not only to reach the small intestines, but to be voided at the mouth. Such instances however are not common. from the minute ends of arteries. This mucus promotes the descent of the alimentary pulp, and, in some measure, defends the inner surface of the intestines from the irritation, to which it would perhaps otherwise be continually exposed, from the aliment; and which, when in a certain degree, excites a painful disorder called colic, a name given to the disease, because its most usual seat is in the intestine colon.

u, The intestines are likewise frequently distended with air, and this distention sometimes occasions pain, and constitutes the flatulent colic.

v, The arteries of the intestines are continuations of the mesenteric arteries, which are derived in two considerable branches from the aorta. The redundant blood is carried back into the vena portarum.

w, In the rectum the veins are called hemorrhoidal; and are there distinguished into internal and external: The first are branches of the inferior mesenteric vein, but the latter pass into other veins. Sometimes these veins are distended with blood from obstructions, from weaknesses of their coats, or from other causes; and what we call the hemorrhoids takes place. In this disease they are sometimes ruptured, and the discharge of blood which consequently follows, has probably occasioned them to be called hemorrhoidal veins.

x, The nerves of the intestines are derived from the eighth pair.

CHAP. VI. Of the Mesentery.

a, The name of the mesentery implies its situation amidst the intestines. It is in fact a part of the peritoneum; being a reduplication (l.) of that membrane from each side of the lumbar vertebrae to which it is firmly attached; so that it is formed of two laminae, connected to each other by cellular membrane.

b, The intestines in their different convolutions form a great number of arches, and the mesentery accompanies them through all these turns; but by being attached only to the hollow part of each arch, it is found to have only a third of the extent of the intestines.

c, That part of this membrane which accompanies the small intestines is the mesentery, properly so called; but those parts of it which are attached to the colon and rectum, are distinguished by the names of meso-colon, and meso-rectum.

d, There are many glands dispersed throughout this double membrane, through which the lacteals and lymphatics pass in their way to the thoracic duct. The blood vessels of the mesentery were described in speaking of the intestines.

e, This membrane, by its attachment to the vertebrae, serves to keep the intestines in their natural situation. The idea usually formed of the colic called mi-

(l.) He who only reads of the reduplication of membranes, will perhaps not easily understand how the peritoneum and pleura are reflected over the viscera in their several cavities; for one of these serves the same purpose in the thorax, that the other does in the abdomen. This disposition, for the discovery of which we are indebted to modern anatomists, seems now to be satisfactorily ascertained, and constitutes a curious part of anatomical knowledge; but the student, unaided by experience, and assisted only by what the limits of this treatise would permit us to say on the occasion, would probably imbibe only confused ideas of the matter; and it will perfectly answer the present purpose, if he considers the mesentery as a membrane attached by one of its sides to the lumbar vertebrae; and by the other, to the intestines.

(m) The hernia congenita will be described with the male organs of generation; with which it is intimately connected.

f, If inflammation takes place, the stricture in this case is increased; and the peristaltic motion of the intestines (by which is meant the progressive motion of the feces downwards) is inverted, and what is called the iliac passion takes place. The same effects may be occasioned by a defect of the intestine, or of the omentum either with it or by itself; and thus constituting what is called an hernia or rupture, a term by which in general is meant the falling down or protrusion of any part of the intestine, or omentum, which ought naturally to be contained within the cavity of the belly.

g, To convey an idea of the manner in which such a defect takes place, it will be necessary to observe, that the lower edge of the tendon of the musculus obliquus abdominis is stretched from the fore-part of the os ilium or iliac bone, to the os pubis; and constitutes what is called Poupart's, or Fallopian's ligament; forming an opening, through which pass the great cural artery and vein. Near the os pubis the same tendinous fibres are separated from each other, and form an opening on each side, called the abdominal ring; through which the spermatic vessels pass in men, and the ligamenta uteri in women. In consequence of violent efforts, or perhaps of natural causes, the intestines are found sometimes to pass through these openings; but the peritoneum which incloses them when in their natural cavity, still continues to surround them even in their defect. This membrane does not become torn or lacerated by the violence, as might be easily imagined, but its dilatability enables it to pass out with the viscus, which it incloses as it were in a bag, and thus forms what is called the hernial sac.

h, If the hernia be under Poupart's ligament, it is called femoral; if in the groin, inguinal; (m) and scrotal if in the scrotum: different names are likewise given to the hernia, as the contents of the sac differ, whether of omentum only, or intestine, or both; but these definitions more properly belong to the province of surgery.

CHAP. VII. Of the Pancreas.

a, The pancreas is one of those glands which anatomists have agreed to call conglomerate; because they are composed of an infinite number of single or conglomerate b, It is placed behind the bottom of the stomach, towards the first vertebra of the loins; being shaped like a dog's tongue, with its point stretched out towards the spleen, and its other end extending towards the duodenum. It is about eight fingers breadth in length, two or three in width, and one in thickness.

c, This viscus, which is of a yellowish colour, somewhat inclined to red, is covered with a membrane which it derives from the peritoneum. Its arteries, which are rather numerous than large, are branches of the splenic; and its veins pass into the veins of the same name; its nerves are derived from the intercostal.

d, The many little glands of which it has been observed the pancreas is composed, all serve to secrete a liquor called the pancreatic juice; which in its colour, consistence, and other properties, does not seem to differ from the saliva. Each of these glands sends out a little excretory duct, which uniting with others, helps to form larger ducts; and all these at last terminate in one common excretory duct, first discovered by Virtusius, in 1642, which runs through the middle of the gland, and is now usually called Ductus Pancreaticus Virtusii. This canal opens into the intestine duodenum, sometimes by the same orifice with the biliary duct, and sometimes by a distinct opening; the liquor it discharges being of a mild and insipid nature, serves to dilute the alimentary pulp, and to incorporate it more easily with the bile.

CHAP. VIII. Of the Liver.

a, The liver is a viscus of considerable size, and of a reddish colour; convex above, and in the forepart where it is placed under the ribs and diaphragm, and of an unequal surface behind. It is chiefly situated in the right hypochondrium, and under the false ribs; but it likewise extends into the epigastric region, where it borders upon the stomach. It is covered by a production of the peritoneum, which serves to attach it by three of its reduplications to the false ribs; these reduplications are called ligaments, though very different in their texture from what are called by the same name in other parts of the body. The umbilical cord too, which in the fetus is pervious, gradually becomes a simple ligament after birth, and by passing to the liver, serves likewise to secure it in its situation.

b, At the posterior part of this organ where the umbilical vessels enter, it is found divided into two lobes; of these, the largest is placed in the right hypochondrium; the other, which covers part of the stomach, is called the little lobe. All the vessels which go to the liver pass in at the fissure we have mentioned, and the production of the peritoneum, which invests the liver, accompanies them in their passage and surrounds them like a glove. The credit of this discovery is due to an English anatomist, in honour of whom, this membranous production is now universally known by the name of Glisson's capsule.

c, The liver was considered by the ancients as an organ destined to prepare and perfect the blood, but later discoveries have proved that this opinion was wrong; and that the liver is a glandular substance formed for the secretion of the bile.

d, The blood is conveyed to the liver by the hepatic artery and the vena porta. This is contrary to the mode of circulation in other parts, where veins only serve to carry off the redundant blood; but, in this viscus, the hepatic artery, which is derived from the celiac, is wholly defined for its nourishment; and the vena porta, which is formed by the union of the veins from all the principal abdominal viscera, only furnishes the blood from which the bile is to be separated; so that these two series of vessels serve very distinct purposes. The vena porta as it ramifies through the liver, performs the office both of an artery and a vein; for it not only carries blood to the liver, but after having deposited its bile, brings back not only its own redundant blood, but likewise that of the hepatic artery into the vena cava.

e, The nerves of the liver are branches of the intercostal and par vagum. The bile after being separated from the mass of blood, in a manner of which mention will be made in another place, is conveyed out of this organ by very minute excretory ducts called porti biliares; these uniting together like the excretory ducts in the pancreas, gradually form larger ones; which at length terminate in a considerable channel called ductus hepaticus.

CHAP. IX. Of the Gall Bladder, its contents and office.

a, The gall bladder is a little membranous bag, shaped like a pear, and attached to the posterior and almost inferior part of the great lobe of the liver.

b, It has three tunics, of which the exterior one is a production of the peritoneum; in the second there are muscular fibres, and the interior coat which is called the nervous tunic, forms several wrinkles on its inner surface, which is supplied with a mucus serving to defend it from the acrimony of the bile.

c, The gall bladder is supplied with blood vessels from the hepatic arteries; these branches are called the cystic arteries, and the cystic veins carry back the blood.

d, Its nerves are derived from the same origin as those of the liver.

e, The neck of the gall bladder is continued in the form of a canal called the ductus cysticus; which soon unites with the ductus hepaticus we described as the excretory duct of the liver, and forming one common canal takes the name of ductus choledochus communis; through which both the cystic and hepatic bile are discharged into the duodenum: this canal opens into the intestine in an oblique direction, first passing thro' the exterior tunic, and then piercing the other coats after running between each of them a very little way; this economy serves two useful purposes, to promote the discharge of bile, and to prevent its return.

a, The bile may be defined to be a natural liquid soap, somewhat fat and bitter, and of a yellowish colour. It easily mixes with water, oil and vinous spirits, and is capable of dissolving resinous substances. Its chemical analysis affords much animal oil, some volatile alkali, and a considerable quantity of water.

b, Its definition seems sufficiently to point out the uses for which it is intended (n). It blends the alimentary mass by dividing and attenuating it; corrects the too great disposition to acuteness which the aliment acquires in the stomach, and finally by its acrimony, tends to excite the peristaltic motion of the intestines.

c. After what has been said, it will be easily conceived that there are two sorts of bile; one of which is derived immediately from the liver thro' the hepatic duct, and the other from the gall bladder. These two biles do not essentially differ from each other. The hepatic bile, however, is milder and more liquid than the gall, which is constantly thicker and yellower; and by being more bitter, seems to possess greater activity than the other.

d. It is generally known that the hepatic bile is secreted from the mass of blood by the liver; but the origin of the cystic bile has occasioned no little controversy amongst anatomical writers. There are some who contend that it is separated in the substance of the liver, from whence it passes into the gall bladder thro' particular vessels (o).

e. There are others who suppose it is secreted by certain vessels in the bladder itself; and there are some writers who consider the gall bladder simply as a reservoir of hepatic bile, which not being perhaps at all times permitted to pass into the intestine, flows back into the cystic duct; and that the difference in the colour, consistence, and taste of the bile, is merely the result of stagnation, increasing in proportion to the length of time it has remained in the reservoir. Again, there are other anatomists who suppose that the bile may be conveyed into the gall bladder by all these means.

f. We will not here relate all the arguments that have been advanced in favour of these several opinions, nor will we aim at establishing any one of them in particular.

g. From whatever source the cystic bile is derived, it seems to be certain, that the gall bladder is a reservoir in which it is collected, and where it gradually thickens. When the stomach is distended with aliment, this reservoir undergoes a certain degree of compression, and the bile passes out into the intestinal canal; and in the efforts to vomit, the gall bladder seems to be constantly affected, and at such times discharges itself of its contents.

(n) The ancients, who were not acquainted with the real use of the liver, considered the bile as an excrementitious and useless fluid.

(o) In deer, and in some other quadrupeds, there seems to be an evident communication, by means of particular vessels, between the liver and the gall bladder. Bianchi of Turin, and the celebrated M. Winiford have both asserted their existence in the human subject, and have named them hepatic-cystic-duets, but later observations tend to prove that no such ducts exist. In obstructions of the cystic duct for instance, the gall bladder has been found shrivelled and empty; and the generality of anatomists of these times, seem to consider the gall bladder as a reservoir of hepatic bile.

(p) These concretions sometimes remain in the gall bladder without causing any uneasiness. Dr Heberden relates, that a gall stone weighing two drachms was found in the gall bladder of the late Lord Bath, though he had never complained of the jaundice, nor of any disorder which he could attribute to that cause. Med. Trans.

(q) The late Mr Hewson of London, in the second part of his experimental inquiries says, he has been led to ascertain the uses of the lymphatic glands, the thymus, and the spleen, which have so long been considered as the Opprobria of anatomists; and he proposed to describe them in a future publication: but that very ingenious physiologist is since dead. An imperfect abstract of his discoveries has appeared in the medical commentaries of Edinburgh, from which we are enabled to collect, that Mr Hewson considered the spleen as an organ of great importance; that he rejected the supposition of its being subservient to the liver, because fluids of greater consequence in the economy are prepared by one organ; that its structure is very analogous to that of the lymphatic glands; that from its being sometimes taken out without inconvenience, he supposed that something else in the system is capable of performing its functions; which he concluded to be the thymus, from their similarity in structure; that he considered the lymphatic vessels, as the only excretory ducts of the spleen; and lastly, that the lymphatic glands concurred with this organ and the thymus, in the formation of the red globules of the blood. CHAP. XI. Of the Glandulae Renales, Kidneys, and Ureters.

a, The glandulae renales, which were by the ancients supposed to secrete the atra bilis, and by them named capsula atrabilariae, are two flat bodies of an irregular figure, one on each side between the kidney and the aorta.

b, In the fetus they are as large as the kidneys, but they do not increase afterwards in proportion to those parts; and in adults and old people, they are generally found shrivelled, and much wasted. They have their arteries and veins. Their arteries usually arise from the splenic or the emulgent, and sometimes from the aorta; and their veins go to the neighbouring veins, or to the vena cava; their nerves are branches of the intercostal.

c, The use of these parts is not yet perfectly known. In the fetus the secretion of urine must be in a very small quantity, and a part of the blood may perhaps then pass thro' these channels, which in the adult is carried to the kidneys, to supply the matter of urine.

a, The kidneys are two in number, situated one on the right, and the other on the left side in the lumbar region, between the last false rib and the os ilium, by the sides of the vertebrae. Each kidney in its figure resembles a sort of bean (x), which from its shape is called kidney bean. The concave part of each kidney is turned towards the aorta and vena cava ascendens. They are surrounded by a good deal of fat, and receive a coat from the peritoneum; and when this is removed, a very fine membrane is found investing their substance and the vessels which ramify through them.

b, Each kidney has a considerable artery and vein, which are called the emulgent. The artery is a branch from the aorta descendens, and the vein passes into the vena cava. Their nerves, which everywhere accompany the blood vessels, arise from a considerable plexus, which is derived from the intercostal.

c, In each kidney, which in the adult is of a pretty firm texture, there are three substances to be distinguished (z). The outer part is glandular or cortical, beyond this is the vascular or tubular substance; and the inner part is papillary or membranous.

d, It is in the cortical part of the kidney that the secretion is carried on; the urine being here received from the minute extremities of the capillary arteries, is conveyed out of this cortical substance by an infinite number of very small cylindrical canals or excretory vessels, which constitute the tubular part. These tubes as they approach the inner substance of the kidney, gradually unite together; and thus forming larger canals, at length terminate in ten or twelve little protuberances called papillae, the orifices of which may be seen without the assistance of glasses. These papillae unite together to form one cavity or reservoir, which is called the pelvis of the kidney (t). From this pelvis the urine is conveyed thro' a membranous canal, which passes out from the hollow side of the kidney, a little below the blood vessels, and is called ureter.

a, The ureters are each about as large as a common writing pen. They are somewhat curved in their course from the kidneys like the letter f, and at length terminate in the posterior and almost inferior part of the bladder, at some distance from each other. They pass into the bladder in the same manner as the ductus choledochus communis passes into the intestinum duodenum; not by a direct passage, but by an oblique course between the several coats; so that the discharge of urine into the bladder is promoted, whilst its return is prevented. Nor does this mode of structure prevent the passage of fluids only from the bladder into the ureters, but likewise air; for air thrown into the bladder inflates it, and it continues to be distended if a ligature is passed round its neck; which seems to prove sufficiently that it cannot pass into the ureters.

CHAP. XII. Of the Urinary Bladder, its office and contents.

a, The urinary bladder is a membranous bag, in urinary shape not unlike a bottle with its neck downwards; situated in the pelvis, between the intestinum rectum and os pubis. The bottom of the bladder is covered by a production of the peritoneum, and it has three other tunics; of these, the external one is composed of fleshy or muscular fibres. The second is called its nervous coat, and within this is its villous coat, which resembles the villous coat of the intestines. The ureters have each the same number of coats, and the whole urinary passage is constantly moistened by a slimy liquor, which defends it against the acrimony of the urine.

b, The neck of the bladder, from which a canal is continued called the urethra, thro' which we discharge the urine; is encircled by muscular fibres, which are distinguished by the name of sphincter vesicae (v).

c, This muscle, by closing the neck of the bladder, prevents an involuntary flow of urine; for without this sphincter it would constantly fall drop by drop from the urethra, as it is distilled thro' the ureters.

a, It will be easily conceived from what has been said, that the kidneys are two glandular bodies thro' which a saline and excrementitious fluid called urine, is constantly separating from the mass of blood; but though anatomists generally agree in asserting that the urine is separated from the blood by the mere action of filtration, yet its appearance is altogether unaccountable upon this supposition. It is impossible to filter from anything what it does not previously contain; and both

(x) The human kidneys are in shape much like the kidneys of sheep. (z) The kidneys in the fetus are distinctly lobulated, and apparently conglomerate in their structure; but in the adult, they become perfectly firm, smooth and regular, and would seem to be glands of the conglomerate kind. (t) The pelvis is not formed by the papillae, as M. Peron and some other writers have believed; but appears to be a distinct membranous bag, sending off processes which embrace the papillae. (v) In compliance with the most general method of anatomical writers, we have described the sphincter vesicae; but there are some modern anatomists who are of opinion, that the neck of the bladder has no muscular fibres; and of this number is M. Lieutard, who contends that the urine is confined in the bladder by means of the levatores ani, and the particular structure of the bladder itself, which he describes as being adapted for this purpose. See Lieutard, Essais Anatomiques. both the blood itself, and the chyle from which it is formed are exceedingly mild, without any saline principle; whereas the urine is full of salts, and those too of such a nature as are scarce to be found anywhere else. See Urine and Chemistry, no. 308.

b, While only a small quantity of urine is collected in the bladder, it excites no kind of uneasiness; but when accumulated to a certain degree, the bladder becomes distended, the salts contained in the urine seem to become more active, and beginning to irritate the inner coat of the bladder, excite in us a certain sensation; which brings on as it were a voluntary contraction of the bladder to promote its discharge: but this contraction is not effected by the muscular fibres of the bladder alone, for all the abdominal muscles contract in obedience to our will, and press downwards all the viscera of the lower belly; and these powers being united, at length overcome the resistance of the sphincter, which dilates and affords a passage to the urine thro' the urethra.

c, The frequency of this evacuation depends on the quantity of urine secreted, on the degree of acrimony it possesses, on the size of the bladder, and on its degree of sensibility.

d, When the urine is loaded with acid salts, a very small quantity of it is sufficient to irritate the inner surface of the bladder, and occasion its discharge; and the same effect will take place when the bladder is by any means inflamed.

e, Every body is conversant with the natural constance of the urine. In a healthy state it is nearly of a straw colour. After being kept some time it deposits a tartarous matter, which is found to be composed chiefly of earth and salt, and soon incrusts the sides of the vessel in which it is contained. While this separation is taking place, appearances, like minute fibres or threads of a whitish colour, will be seen in the middle of the urine, and an oily foam will be observed floating on its surface. So that the most common appearances of the urine are sufficient to ascertain that it is not pure water, but a ferocity, impregnated with earthly, saline, and oily particles.

f, The urine is not always voided of the same colour and consistence; for there are found to depend on the proportion of its watery part to that of its other constituent principles. Its colour and degree of fluidity seem to depend on the quantity of saline and inflammable particles contained in it; so that an increased proportion of those parts will constantly give the urine a higher colour, and add to the quantity of sediment.

g, The variety in the appearance of the urine, depends on the nature and quantity of solid and fluid aliment we take in; and it is likewise occasioned by the different state of the urinary vessels; by which we mean the channels thro' which it is separated from the blood, and conveyed thro' the pelvis into the ureters. If these passages are contracted, in consequence of inflammation, or any other means, their diameter is of course diminished; they permit only the more limpid parts of the blood to pass through them, and the urine is found to be perfectly clear and colourless like pure water. But,

Vol. I.

(v) The reader must consider this, only as one among many other causes of calculous concretions in the urinary passages, which are to be looked for in the natural constitution of the body, mode of life, &c. The urine itself, in people who have much natural tendency to these complaints, though seemingly pure and limpid when first secreted, has a wonderful disposition to concrete.

if, on the contrary, their diameter is increased, they not only afford a passage to the watery part, which presents itself for secretion, but likewise to an increased quantity of other particles, which consequently give the urine a higher colour and add to its consistence.

h, If the urinary vessels are naturally of too loose and soft a texture, they will sometimes admit groser particles (v), which they will not always be able to carry off; and these particles will not fail to accumulate in the canal, and occasion those painful dilatations of it, which constitute the nephritic colic. The seat of this disease is sometimes in the kidney itself, and sometimes in the ureters; depending on the part where the passage of these concretions to the bladder is obstructed. When these concretions, or any extraneous body admitted into the bladder, continue to reside in it, they become a nucleus to a calculus; and if the urine continues to have a disposition to add to it, it gradually increases in size, and what is called a calculus or stone, is formed in the bladder; which can only be extracted by the operation of lithotomy, unless nature, by a favourable effort as is very often the case, carries it out of the bladder before it becomes too large to pass into the urethra.

i, Having been observed, that after drinking any light wine or Spa water, it very soon passed off by urine, it was supposed by some anatomists that the urine is not altogether conveyed to the bladder by the ordinary course of circulation, but that there must certainly exist some other shorter means of communication, perhaps by certain vessels between the stomach and the bladder; or that the fluid transeudes thro' the coats of the stomach, and is then taken into the bladder by absorption; but, from some experiments on living animals, others have denied the truth of this doctrine. If we open the belly of a dog, press out the urine from the bladder, pass a ligature round the emulgent arteries, and then sew up the abdomen, and give him even the most diuretic liquor to drink, the stomach and other channels will be distended with it, but not a drop of urine will be found to have passed into the bladder. This experiment then, seems to prove that all the urine we evacuate is conveyed to the kidneys thro' the emulgent arteries, in the manner already described. It is true that wine and other liquors promote a speedy evacuation of urine, but the discharge seems to be merely the effect of the stimulus they occasion; by which the bladder and urinary parts are solicited to a more copious discharge of the urine, which was before in the body, and not immediately of that which was last drank; and this increased discharge, if the supply is kept up, will continue: nor will this appear wonderful, if we consider the great capacity of the vessels which go to the kidneys, the constant supply of fresh blood which is essential to health, and the rapidity with which it is incessantly circulated through the heart to all parts of the body.

Chap. XIII.

The instruments and process of Digestion.

a, By digestion is to be understood the changes the aliment aliment undergoes for the formation of chyle; these changes are effected in the mouth, stomach, and small intestine.

b. The mouth, of which every body has a general knowledge, is the cavity between the two jaws, the fore part and sides of which are formed by the lips, teeth, and cheeks; the back part terminating in the throat.

c. The lips and cheeks are made up of fat and muscles, covered by the cuticle, which is continued over the whole inner surface of the mouth, like a fine and delicate membrane. Besides this membrane, the inside of the mouth is furnished with a spongy and very vascular substance, called the gums, by means of which the teeth are secured in their sockets. A similar substance covers the roof of the mouth, and forming what is called the velum palati, terminates in a soft, small, and conical body, called the uvula; which appears as it were suspended from the middle of the arch over the basis of the tongue.

d. The tongue is composed of several muscles which enable it to perform a variety of motions, for the articulation of the voice, for the purposes of mastication, and for conveying the aliment into the pharynx. Its upper part is covered with papillae, which constitute the organ of taste, and are easily to be distinguished; it is covered by the same membrane that lines the inside of the mouth, and which makes at its inferior part towards its basis a reduplication called the frenum.

e. Under the velum palati, and at the basis of the tongue, is the pharynx; which is the beginning of the oesophagus, stretched out every way so as to resemble the top of a funnel, through which the aliment passes into the stomach.

f. The mouth has a communication with the nostrils, at its posterior and upper part; with the ears by the cutaneous tubes; with the lungs by means of the larynx; and with the stomach by means of the oesophagus.

g. The pharynx is constantly moistened by a fluid secreted by two considerable glands, called the tonsils; one on each side of the velum palati. These glands, from their supposed resemblance to almonds, have likewise been called amygdalae. The tonsils, from some vicious disposition in the fluid they secrete, or from other causes, sometimes swell, and constitute what is called a balsam quinsy. In the true quinsy, which is a very acute disease, the pharynx or larynx, and sometimes both at the same time, are affected.

h. The mouth is moistened by a considerable quantity of saliva. This humour is derived from the parotid glands, a name by which its etymology points out their situation to be near the ear. They are two in number, one on each side under the os malis, and are of the conglomerate kind; being formed of many smaller glands, each of which sends out a very small excretory duct, which uniting with each other, form one common channel, that runs over the cheek, and piercing the buccinator muscle, opens into the mouth on each side, by an orifice into which a bristle may be easily introduced. Besides these, the maxillary glands, which are placed near the inner surface of the angle of the lower jaw on each side; the sublingual glands, which are situated at the root of the tongue; and the glands of the palate, which are seated in the velum palati; together with many other less considerable ones, pour the saliva into the mouth through their several excretory ducts.

i. The saliva, like all the other humours of the body, is found to be different in different people; but in general, it is a limpid and insipid fluid, without smell in healthy subjects; and these properties would seem to prove that it contains very few saline or inflammable particles. It is so much disposed to fermentation, that the inhabitants of Otaheite, and other barbarous nations, use it by way of yeast, to make their liquors ferment.

k. The uses of the saliva seem to be to moisten and lubricate the mouth, and to assist in reducing the aliment into a soft pulp before it is conveyed into the stomach.

a. The variety of functions which are constantly performed by the living body, must necessarily occasion a continual waste and dissipation of its several parts. A great quantity is every day thrown off by the insensible perspiration and other discharges; and were not these losses constantly recruited by a fresh supply of chyle, the body would soon effect its own dissolution. But nature has very wisely favoured us with organs fitted to produce such a supply, and has at the same time endowed us with the sensations of hunger and thirst, that our attention may not be diverted from the necessary business of nutrition. Hurried on by the occurrences of life, we should perhaps without these admonitions, sometimes omit to take in the proper supply of aliment; but the demands of hunger are not to be withstood. This sensation is universally known; but it would perhaps be difficult to describe it perfectly in words. In describing the stomach, mention was made of the gastric juices, as everywhere lubricating its inner coat. This humour mixes itself with the aliment in the stomach, and helps to prepare it for its passage into the intestine; but when the stomach is perfectly empty, this same fluid irritates the coats of the stomach itself, and produces the sensation of hunger.

b. A certain proportion of liquid aliment is required to assist in the process of digestion, and to afford that moisture to the body, of which there is such a constant dissipation. Thirst induces us to take this necessary supply of drink; and the seat of this sensation is in the tongue, fauces, and oesophagus, which from their great sensibility are required to be kept moist; for although the fauces are naturally moistened by the mucus and salivary juices, yet the blood, when deprived of its watery part, or rendered acrimonious by any natural cause, never fails particularly to affect these parts, and the whole alimentary canal, and to occasion thirst. This is the common effect of fevers, and of hard labour; by both which too much of the watery part of the blood is dissipated.

a. It has been observed that the aliment undergoes some preparation in the mouth before it passes into the stomach; and this preparation is the effect of mastication. In treating of the upper and lower jaws, mention was made of the number and arrangement of the teeth. The upper jaw was described as being immovable; but the lower jaw was spoken of as being capable of elevation and depression, and of a grinding motion. The aliment, when first carried into the mouth, is pressed between the teeth of the two jaws by a very strong force. strong and frequent motion of the lower jaw; and the tongue and the cheeks afflicting in this process, continue to replace the food between the teeth till it is perfectly divided, and reduced to the consistence of pulp. The incisors and canines divide it first into smaller pieces; but it is between the surfaces of the dentes molares, by the grinding motion of the jaw, that the mastication is completed.

b. During this process, the salivary glands being gently compressed by the contraction of the muscles that move the lower jaw, and somewhat stimulated by the saline particles of the aliment, pour out their saliva, which helps to divide and break down the food, which at length becomes a kind of pulp, and is then carried over the basis of the tongue into the faucies. But to effect this passage into the oesophagus, it is necessary that the other openings which were mentioned as having a communication with the mouth as well as the pharynx, should be closed; that none of the aliment, whether solid or liquid, may pass into them, whilst the pharynx alone is dilated to receive it; such a disposition actually takes place in a manner we shall endeavour to describe.

c. The trachea arteria or windpipe, through which the air is conveyed to the lungs, is placed before the oesophagus in the act of swallowing; then if the larynx is not closed, (for so the upper part of the trachea is called,) the aliment will pass into it in its way to the oesophagus. But this is prevented by a small and very elastic cartilage, called epiglottis, which is attached only to the forepart of the larynx; so that the food in its passage to the oesophagus, presses down this cartilage which then covers the glottis, or opening of the larynx; and at the same time the velum palati being capable of some degree of motion, is drawn backwards by its muscles, and closes the openings into the nose and the eustachian tubes: this is however not all. The larynx, which being composed of cartilaginous rings, cannot fail in its ordinary state to compress the membranous canal of the oesophagus, is, in the act of deglutition, carried forwards and upwards by muscles destined for that purpose; and consequently drawing the forepart of the pharynx with it, that opening is fully dilated. When the aliment has reached the pharynx, its descent is promoted by its own proper weight, and by the muscular fibres of the oesophagus, which continue to contract from above downwards, until the aliment has reached the stomach. That these fibres have no inconsiderable share in deglutition, any person may experience, by swallowing with his head downwards, when the descent of the aliment cannot possibly be effected by its weight.

d. It is necessary that the nostrils and the lungs should communicate with the mouth, for the purposes of speech and respiration; but if the most minute part of our food happens to be introduced into the trachea, it never fails to produce a violent cough, and sometimes the most alarming symptoms; this is liable to happen when we laugh or speak, in the act of deglutition. The food is then said to have passed the wrong way; and indeed this is not improperly expressed, for death would soon follow, if the quantity of aliment introduced into the trachea should be sufficient to obstruct the respiration only during a very short time; or if the irritating particles of food should not soon be thrown up again by means of the cough, which in these cases very reasonably increases in proportion to the degree of irritation.

e. If the velum palati did not close the passage to the nostrils, deglutition would be performed with difficulty, and perhaps not at all; for the aliment would return thro' the nose, as is sometimes the case in drinking. Children, from a deficiency in this velum palati, have been seen to die a few hours after birth; and they who from disease or any other cause have not this part perfect, swallow with difficulty.

f. The aliment, after having been sufficiently divided by the action of the teeth, and attenuated by the saliva, is received into the stomach, where it is destined to undergo a more considerable change.

g. The properties of the aliment not being much altered at its first entrance into the stomach, and before it is thoroughly blended with the gastric juice, is capable of irritating the inner coat of the stomach to a certain degree, and occasions a contraction of its two orifices. In this membranous bag, surrounded by the abdominal viscera, and with a certain degree of natural heat, the aliment undergoes a constant agitation by means of the abdominal muscles, and of the diaphragm, and likewise by a certain contraction or expansion of the muscular fibres of the stomach itself. By this motion, every part of the food is exposed to the action of the gastric juice, which gradually divides and attenuates it, and prepares it for its passage into the intestines.

h. The more the particles of food have imbibed of the gastric juice, the less obstacle do they afford to the expansion of the air which is set loose by the process of digestion; and being rarified by the warmth of the stomach, tends to complete the perfect dissolution of the alimentary pulp.

(w) Mr J. Hunter has lately obliged the public with the account of a very singular fact in the animal economy, which seems to throw considerable light on the principles of digestion: he informs us, that there are few dead bodies in which the stomach at its great end, is not found to be in some degree digested; he observes, that animals, or parts of animals, possessed of the living principle, when taken into the stomach, are not in the least affected by the action of that viscus; but that the moment they lose the living principle, they become subject to its digestive powers. This he supposes to be the case with the stomach, which is enabled to resist the action of its juices in the living body, but when deprived of the living principle, is then no longer able to resist the power of that menstruum, which it had itself formed for the digestion of its contents; the process of digestion appearing to be continued after death. Mr Hunter was confirmed in his ideas on this subject by observing what happens in the stomachs of fishes: they frequently swallow without mastication, fish which are larger than the digesting parts of their stomach can contain, and in such cases that part which is taken into the stomach, is more or less dissolved; while that part which remains in the oesophagus, is perfectly found; and here, as well as in the human body, the digesting part of the stomach is often reduced to the same state as the digested part of the food. These appearances the ingenious writer imagines, lead to prove that digestion is not effected by a mechanical power, by contractions of the stomach, or by heat; but by a fluid secreted in the coats of the stomach, which is poured into its cavity, and there animalizes the food, or assimilates it to the nature of blood.——Philos. Trans. Vol. 61. The food, after having remained during one, two, or three hours in the stomach, is converted into a greyish pulp, which is usually called chymus, a word of Greek etymology, signifying juice; and some few milky or chylous particles begin to appear; but the term of its residence in this bag is proportioned to the nature of the aliment, and to the state of the stomach and its juices. The thinner and more perfectly digested parts of the food, pass by a little at a time, into the duodenum, through the pylorus, the fibres of which relax to afford it a passage; and the groarser and less digested particles remain in the stomach till they acquire a sufficient fluidity to pass into the intestines, where the nature of the chymus is perfectly changed. The bile and pancreatic juice which flow into the duodenum, and the mucus which is everywhere distilled from the surface of the intestines, mix themselves with the alimentary pulp, which they still farther attenuate and dissolve, and into which they seem to infuse new properties.

Two matters very different from each other in their nature and definition, are the result of this combination. One of these which is composed of the liquid parts of the aliment, and of some of its more solid particles, extremely divided and mixed with the juices we have described, constitutes a very mild, sweet, and whitish fluid, resembling milk, and distinguished by the name of chyle. This fluid is absorbed by the lacteals, which convey it into the circulation, where by being assimilated into the nature of blood, it affords that supply of nutrition which the continual waste of the body is found to require. The other is the remains of the alimentary mass deprived of all its nutritious particles, and containing only such parts, as by their acrimony or their cohesion, were rejected by the absorbing mouths of the lacteals. This groarser part called the feces, passes on through the course of the intestines to be voided at the anus, as will be explained hereafter, for this process in the economy cannot well be understood till the motion of respiration has been explained. But the structure of the intestines is a subject which may be properly described in this place, and deserves to be attended to.

It has been already observed, that the intestinal canal is five or six times as long as the body, and that it forms many circumvolutions, in the cavity of the abdomen, which it traverses from the right to the left, and again from the left to the right; in one place descending, and in another extending itself upwards. It was noticed likewise, that the inner coat of the intestines by being more capacious than their exterior tunics, formed a multitude of plaited placed at a certain distance from each other, and called valvulae conniventes. Now this disposition will be found to afford a farther proof of that divine wisdom, which the anatomist and physiologist cannot fail to discover in all their pursuits; for if the intestinal canal was much shorter than it naturally is, if instead of its present circumvolutions it passed in a direct course from the stomach, and if its inner surface was smooth and destitute of valves, the aliment would consequently pass with great rapidity to the anus, and sufficient time would be wanting to assimilate the chyle, and for the necessary absorption of it into the lacteals; so that the body would be deprived of the supply of nutrition, which is so essential to life and health, but the length and circumvolutions of the intestines, the inequality of their internal surface, and the course of the aliment through them, all concur to perfect the separation of the chyle from the feces, and to afford the necessary nourishment to the body.

Digestion is performed with more or less ease, according to the temperaments, age, sex, strength, exercise, passions, &c. In some it is long and difficult, in others quick and easy, in its process. Every one ought to adapt the quantity and kind of aliment he takes in, to the state of his stomach and the powers of its juices, which can only be learned by experience and attentive observation.

It seems to be very easy to demonstrate, that he who loads his stomach with more than he is able to digest, will derive from it only a crude and imperfect chyle, by no means calculated to afford a good and wholesome blood, and to promote a healthy constitution of body.

In a recovery from sickness, the patient often thinks he is making hasty advances towards health, by eating more than his stomach will perhaps allow him to take in with ease; and he is led to imagine that his strength will increase in proportion to the quantity he eats and drinks; but on this point his notions are erroneous; for the stomach, like all other parts impaired by sickness, recovers its tone slowly, and is unable to assimilate such a load of materials into chyle; so that the digestion is crude and imperfect, and the blood, as well as the other juices of the body, partaking of the vicious properties of the chyle, the recovery of health is rather retarded than promoted, and sometimes other diseases are produced. Whereas, by taking in a less quantity of food at a time, the stomach is enabled to digest it perfectly, and to afford that wholesome and perfect supply of chyle, which will not fail to nourish the body and restore it to health. For it is worthy of observation, that nutrition is not derived altogether from the quantity we eat, but from the quantity we digest.

CHAP. XIV.

Of the course of the Chyle, and of the Lymphatic System.

An infinite number of very minute vessels called of the lacteals, arise like net-work from the inner surface of the intestines, but principally from the jejuno-ileum and ilium, which are destined to imbibe the nutritious fluid or chyle. These vessels pass obliquely thro' the coats of the intestine, and, running along the mesenteries, unite as they advance, and form larger branches, all which pass through the mesenteric or conglomerate glands, which are very numerous in the human subject. As they run between the intestines and these glands, they are styled vena lactea primi generis; but after leaving these glands, they are found to be less numerous, and being increased in size, are then called vena lactea secundi generis, which go to deposit their contents in the thoracic duct, thro' which the chyle is conveyed into the blood.

This thoracic duct begins about the lower part of the first vertebra lumborum, from whence it passes up by the side of the norta, between that and the vena azigos close to the vertebra, being covered by the pleura. Sometimes it is found divided into two branches. branches, but they usually unite again into one canal, which opens into the left subclavian vein, after having run a little way in an oblique course between its coats. The subclavian vein communicates with the vena cava, which passes to the right auricle of the heart.

c, The lower part of this duct being usually larger than any other part of it, has been named receptaculum chylis, or Pecquet's receptacles, in honour of the anatomist who first discovered it in 1651. In some quadrupeds, in turtle, and in fish, this enlargement is more considerable in proportion to the size of the duct, than it usually is in the human subject, where it is not commonly found large enough to merit the name of receptaculum.

d, The opportunities of observing the lacteals in the human subject, do not often occur; but they may easily be demonstrated in a dog or any other quadruped that is killed two or three hours after feeding upon milk, for then they appear filled with white chyle.

e, But these lacteals which we have described as passing from the intestines through the mesentery to the thoracic duct, compose only a part of a system of vessels which perform the office of absorption, and which constitute with their common trunk the thoracic duct, and the conglomerate glands which are dispersed through the body, what may be styled the lymphatic system. So that what is said of the structure of one of these series of vessels, may very properly be applied to that of the other.

a, The lymphatic veins (x) are minute pellucid tubes, which, like the lacteals, direct their course towards the centre of the body, where they pour a colourless fluid into the thoracic duct. The lymphatics from all the lower parts of the body, gradually unite as they approach this duct, into which they enter by three or four very large trunks, which seem to form the lower extremity of this canal, or receptaculum chylis. The lacteals open into it near the same place, and the lymphatics from all the upper parts of the body, pour their lymph into different parts of this duct as it runs upwards to terminate in the left subclavian vein.

b, As the lymphatics commonly lie close to the large blood vessels, as a ligature passed round the crural artery in a living animal, by including the lymphatics, will occasion a distention of these vessels below the ligature so as to demonstrate them with ease; and a ligature passed round the thoracic duct, instantly after killing an animal, will, by stopping the course of its contents into the subclavian vein, distend not only the lacteals, but also the lymphatics in the abdomen and lower extremities with their natural fluids (y).

c, The coats of these vessels are too thin to be separated from each other; but the mercury they are capable of sustaining, proves them to be very strong; and their great power to contract after undergoing considerable distention, together with the irritability with which Baron Haller found them to be ended, seems to render it probable, that, like the blood-vessels, they have a muscular coat.

d, The lymphatics are nourished after the same manner as all the other parts of the body. For even the most minute of these vessels are probably supplied with still more minute arteries and veins. This seems to be proved by the inflammation of which they are susceptible; and the painful swellings which sometimes take place in lymphatic vessels, prove that they have nerves as well as blood vessels.

e, Both the lacteals, lymphatics, and thoracic duct, are furnished with valves which are much more common in these vessels than in the red veins. These valves are usually in pairs, and serve to promote the course of the chyle and lymph towards the thoracic duct, and to prevent its return. Mention has been made of the glands, through which the lacteals pass in their course thro' the mesentery; and it is to be observed, that the lymphatics pass through similar glands in their way to the thoracic duct. These glands are all of the conglomerate kind, but the changes which the chyle and lymph undergo in their passage through them have not yet been ascertained.

f, The lymphatic vessels begin from surfaces and cavities in all parts of the body as absorbers (z). This is a fact now universally allowed; but how the fluids they absorb are poured into those cavities, is a subject of controversy among the anatomists of these times. The contents of the abdomen, for instance, were described as being constantly moistened by a very thin watery fluid. The same event takes place in the pericardium, pleura, and all the other cavities of the body, and this watery fluid is the lymph. But whether it is exhaled into those cavities through the minute ends of arteries, or transuded through their coats, are the points in dispute. We cannot here be permitted to relate the many ingenious arguments that have been advanced in favour of each of these opinions; nor is it perhaps of consequence to our present purpose, to enter into the dispute. It will be sufficient if the reader can form an idea of what the lymph is, and of the manner in which it is absorbed.

g, The lymph, from its transparency and want of colour, would seem to be nothing but water; and hence the first discoverers of these vessels styled them ductus aquosus; but experiments prove that the lymph of a healthy animal coagulates by being exposed to the air, or

(x) The arteries in their course through the body becoming gradually too minute to admit the red globules of the blood, have been styled capillary or lymphatic arteries. The vessels which are here described as constituting the lymphatic system, were at first supposed to be continued from those arteries, and intended to convey back the lymph either into the red veins or the thoracic duct, the office of absorption having been attributed to the red veins. But succeeding anatomists have clearly demonstrated, that the lymphatic veins are not continuations of the lymphatic arteries, but that they constitute the absorptive system. There are still however some very respectable names among the anatomists of the present age, who contend, that the red veins act likewise as absorbers; but it seems to have been clearly proved, that the red veins do absorb no where but in the cavernous cells of the penis, the erection of which is occasioned by a distention of those cells with arterial blood.

(y) In the dead body they may be easily demonstrated by opening the artery ramifying through the viscera, as in the spleen for instance, and then throwing in air; by which the lymphatics will be distended. One of them may then be punctured, and mercury introduced into it through a blow pipe.

(z) Lymphatics have never yet been discovered in the brain; though it would seem probable from analogy, that this organ is not destitute of them. or a certain degree of heat, and likewise by being suffered to rest; seeming to agree in this property with that part of the blood called the coagulable lymph. This property of the lymph leads to determine its use in moistening and lubricating the several cavities of the body, in which it is found; and for which, by its gelatinous principle, it seems to be much better calculated than a pure watery fluid would be, for such it has been supposed to be by some anatomists.

h. The mouths of the lymphatics and lacteals, by acting as capillary tubes, seem to absorb the lymph and chyle, in the same manner as a capillary tube of glass, when put into a basin of water, will be enabled to attract the water into it to a certain height. In the opinion of most natural philosophers, the lymph or the chyle is conveyed upon this principle, as far as the fifth pair of valves, which seem to be placed not far from the orifice of the absorbing vessel, whether lymphatic or lacteal; and the fluid will then be propelled forwards by a continuation of the absorption at the orifice. But this does not seem to be the only inducement to its progress towards the thoracic duct; these vessels have probably a muscular coat, which may serve to press the fluid forwards from one pair of valves to another; and as the large lymphatic vessels and the thoracic duct are placed close to the large arteries, which have a considerable pulsation, it is reasonable to suppose that they derive some advantages from this situation.

**Chap. XV.**

**Of the Generative Organs.**

a. The male organs of generation have been usually divided into the parts which serve to prepare the semen from the blood, and those which are destined to convey it into the womb. But it seems to be more proper to distinguish them into the preparing, the containing, and the expelling parts, which are the different offices of the testes, the vesiculae seminales, and the penis; and this is the order in which we propose to describe them.

b. The testes are two glandular bodies serving to secrete the semen from the blood. They are originally formed and lodged within the cavity of the abdomen, and it is not till after the child is born, or very near that time, that they begin to pass into the groin, and from thence into the scrotum. By this disposition they are very wisely protected from the injuries to which they would be liable to be exposed, from the different positions and dispositions of the child at the time of parturition.

c. The testicles in this state are loosely attached to the psoas muscles by means of the peritoneum by which they are covered; and they are at this time of life connected in a very particular manner to the parietes of the abdomen, and likewise to the scrotum, by means of a substance which Mr Hunter calls the ligamentum, or gubernaculum testis; because it connects the testis with the scrotum; and directs its course in its descent; this gubernaculum he describes, as being of a pyramidal form, with its bulbous head fixed to the lower end of the testis and epididymis, and as losing its lower and slender extremity in the cellular membrane of the scrotum. Mr Hunter says, it is difficult to ascertain what the structure and composition of this gubernaculum is; but he thinks it is certainly vascular and fibrous; and from certain circumstances is led to suspect, that it is in part composed of the cremaster muscle running upwards to join the lower end of the testis.

d. We are not to suppose that the testicle when descended into the scrotum, is to be seen loose as a piece of gut or omentum would be in a common hernial sac. We have already observed, that during its residence in the cavity of the abdomen, it is attached to the peritoneum, which descends with it; so that when the sac is completed in the scrotum, the testicle is at first attached only to the posterior part of it, while the foreskin lies loose, and for some time affords a communication with the abdomen. The spermatic chord, which is made up of the spermatic artery and vein, and of the vas deferens or secretory duct of the testis, is closely attached behind to the posterior part of this elongation of the peritoneum. But the foreskin part of the peritoneal sac, which is at first loose, and not attached to the testicle, closes after a certain time, and becomes united to the posterior part, and thus perfectly surrounds the testicle as it were in a purse.

e. The testicles of the fetus differ only in their size and situation from those of the adult; in their passage from the abdomen they descend through the abdominal rings into the scrotum, where they are supported and defended by various integuments.

f. What the immediate cause of this descent is, has not yet been satisfactorily determined. It has been ascribed to the effects of respiration, but the testicles have sometimes been found in the scrotum before the child has breathed; and it does not seem to be occasioned by the action of the cremaster muscle, because the same effect would be liable to happen in the hedgehog, and some other quadrupeds, whose testicles remain in the abdomen during life.

g. The scrotum, which is the external or common covering of both testicles, is a kind of sac formed by the common integuments; and externally divided into two equal parts by a prominent line, called raphe.

h. In the inner part of the scrotum we meet with a cellular coat called dartor, which by its duplicature, divides the scrotum into two equal parts, and forms what is called septum scroti, which corresponds with the raphe. The colliquation which is so often observed to take place in the scrotum of the healthy subject, when excited by cold or by the stimulus of venery, is by some attributed to the contractile motion of the skin, and not to any muscular fibres, as is the case in dogs and some other quadrupeds.

i. The scrotum then, by means of its septum, is found to make two distinct bags in which the testicles, invested by their proper tunics, are securely lodged and separated from each other. These coats are the cremaster, the tunica vaginalis, and the tunica albuginea. The first of these is composed of muscular fibres, and is to be considered only as a partial covering of the testis; for it surrounds only the spermatic chord, and terminates upon the upper and external parts of the tunica vaginalis testis; serving to draw up and suspend the testicle. The tunica vaginalis testis has already been described, as being originally a thin production of the peritoneum, loosely adhering every where to the testicle, which it includes as it were in a bag. The tunica albuginea, is a firm, white, and very compact membrane, of a glistering appearance; which immediately invests invests the body of the testis and the epididymis; serving in some measure to connect them to each other, but without extending itself at all to the spermatic chord. This tunica albuginea serves to confine the growth of the testis and epididymis within certain limits, and by giving them a due degree of firmness, enables them to perform their proper functions.

k. Having removed this last tunic, we discover the substance of the testicle itself, which appears to be made up of an infinite number of very elastic filaments, which may be best distinguished after macerating the testicle in water. Each testicle is made up of the spermatic artery and vein, and the excretory vessels or tubuli seminiferi. There are likewise a great number of absorbent vessels, and some branches of nerves to be met with in the testicles.

l. The spermatic arteries arise one on each side from the aorta, generally about an inch below the eminence. The right spermatic vein commonly passes into the vena cava; but the left spermatic vein usually empties itself into the cava on that side; and it is supposed to take this course into the eminence, that it may avoid passing over the aorta, which it would be obliged to do in its way to the vena cava.

m. The blood is circulated very slowly through the spermatic artery, which makes an infinite number of convolutions in the substance of the testicle, where it deposits the semen, which passes through the tubuli seminiferi. These tubuli seminiferi are seen running in short waves from the tunica albuginea to the axis of the testicle; and are divided into distinct portions by certain thin membranous productions, which originate from the tunica albuginea. They at length unite, and by an infinite number of convolutions form a sort of appendix to the testis, called epididymis; which is a vascular body of an oblong shape, situated upon the superior part of each testicle. These tubuli of the epididymis, at length form an excretory duct, called vas deferens; which ascends towards the abdominal rings, with the other parts that make up the spermatic chord, and then a separation takes place; the nerves and blood vessels passing on to their several terminations, and the vas deferens going to deposit its semen in the vesicula seminalis, which are two soft bodies of a white and convoluted appearance externally, situated obliquely between the rectum and the lower part of the bladder, and uniting together at their lower extremity. From these reservoirs, which are plentifully supplied with blood-vessels and nerves, the semen is occasionally discharged through two short passages, which open into the urethra, close to a little eminence called verumontanum.

n. Near this eminence we meet with the prostate, which is situated at the neck of the bladder, and is described as being of a glandular structure. It is shaped somewhat like a heart with its small end foremost, and invests the origin of the urethra. It is supposed to secrete a whitish and cream-like liquor, which is discharged into the urethra on each side of the openings of the vesicula-seminalis, at the same time, and from the same cause that the semen is expelled; to which it seems to give a white colour and considerable viscosity; the semen we meet with in the vesicula-seminalis of the dead subject being exceedingly limpid.

o. The penis which is to be considered as the vehicle, or active organ of procreation; is composed of two columns, the corpora cavernosa, and corpus spongiosum. The corpora cavernosa, which constitute the greatest part of the penis, may be described as two cylindrical, ligamentous tubes, each of which is composed of an infinite number of minute cells of a spongy texture, which communicate with each other. These two bodies are of a very pliant texture, and capable of considerable dilatation; and being united laterally to each other, occasion by this union, a space above, and another below. The uppermost of these spaces is filled by the blood-vessels, and the lower one which is larger than the other by the urethra. These two cavernous bodies are at first only separated by a partition of tendinous fibres, which allow them to communicate with each other; but they afterwards diverge from each other like the branches of the letter Y, and diminishing gradually in size, are attached, one on each side, by means of the ligamentum suspensorium penis, to the ramus pubis, and to the inferior portion of the os pubis.

p. The corpus spongiosum penis or corpus spongiosum urethrae, as it is styled by some authors, begins as soon as the urethra has passed the prostate, with a thick origin almost like a heart, fixed under the urethra, and afterwards above it, becoming gradually thinner; and surrounding the whole canal of the urethra, till it terminates in a considerable expansion, and constitutes what is called the glans penis, which is exceedingly vascular, and covered with papillae like the tongue. The cuticle which lines the inner surface of the urethra, is continued over the glans in the same manner as it is spread over the lips.

q. The penis is invested by the common integuments, but the cutis is reflected back every where from the glans as it is in the eye lids, so that it covers this part when the penis is in a relaxed state as it were with a hood, and from this use is called prepuce.

r. The prepuce is tied down to the under part of the glans by a small ligament called frenum, which is in fact only a continuation of the cuticle and cutis. There are many simple sebaceous follicles called glandulae odoriferae, placed round the basis of the glans; and the fluid they secrete serves to preserve the exquisite sensibility of this part of the penis, and to prevent the ill effects of attrition from the prepuce.

s. The urethra may be defined to be a membranous canal passing from the bladder through the whole extent of the penis. Several very small openings called lacunae, communicate with this canal, through which a mucous is supposed to be discharged into it; and besides these, there are other glands first described by Cowper, as secreting a fluid for lubricating the urethra, and called Cowper's glands; and M. Littre speaks of a gland situated near the prostate, as being destined for the same use.

t. The urethra being continued from the neck of the bladder, is to be considered as making part of the urinary passage; and it likewise affords a conveyance to the semen, which we have observed is occasionally discharged into it from the vesicula-seminalis. The direction of this canal being first under, and then before the pubis, occasions a winding in its course from the bladder to the penis, not unlike the turns of the letter S.

u. The penis has three pair of muscles, the ereciones, acceleratores, and transversales. The first originate from the tuberosity of the ischium, and terminate in the cor- pore cavernosa. The acceleratores arise from the sphincter, and by their insertion serve to compress the bulbous part of the urethra; and the transversales are destined to afford a passage to the semen, by dilating the canal of the urethra.

v. The arteries of the penis are chiefly derived from the internal iliacs. Some of them are supposed to terminate by papulous orifices within the corpora cavernosa, and corpus spongiosum; and others terminate in veins, which at last make up the vena magna dorsi penis, and other smaller veins which are in general distributed in like order with the arteries.

w. Its nerves are large and numerous; they arise from the great sciatic nerve, and accompany the arteries in their course through the penis.

x. We have now described the anatomy of this organ, and there only remains to be explained, how it is enabled to attain that degree of firmness and distention which is essential to the great work of generation.

y. The greatest part of the penis has been spoken of, as being of a spongy and cellular texture plentifully supplied with blood vessels and nerves; and as having muscles to move it in different directions: now, the blood is constantly passing into its cells through the small branches of the arteries which open into them, and is from thence as constantly absorbed by the papulous orifices of some of its veins, so long as the corpora cavernosa and corpus spongiosum continue to be in a relaxed and pliant state. But when from any nervous influence or other means, which it is not necessary here to define or explain, the erectores or other muscles of the penis, are induced to contract; the veins undergo a certain degree of compression, and the passage of the blood through them is so much impeded that it collects in them a greater proportion than they are enabled to carry off: so that the penis gradually enlarges, and being more and more forcibly drawn up against the os pubis, the vena magna itself is at length compressed, and the penis becomes fully distended. But as the causes which first occasioned this distention subside, the penis gradually returns to its state of relaxation.

a. Anatomical writers usually divide the female organs of generation into external and internal. In the first division they include the mons veneris, labia pudendi, perineum, clitoris, nymphæ, and carunculae myrtiformes; and in the latter, the vagina, with the uterus and its appendages.

b. The mons veneris which is placed on the upper part of the symphysis pubis, is internally composed of adipose membrane which makes it soft and prominent: it divides into two parts called labia pudendi, which descending towards the rectum, from which they are divided by the perineum, form what is called the fourchettes. The perineum is that fleshy space which extends about an inch and a half from the fourchettes to the anus, and from thence about two inches to the coccyx.

c. The labia pudendi being separated, we observe a fulcus called fossa magna; in the upper part of which is placed the clitoris, a small round spongy body, in some measure resembling the male penis, but imper-

(v) Although in conformity to the generality of writers, the clitoris is here described as having two pair of muscles, the erectores alone seem strictly to belong to it: the sphincter vaginae having no connection with the clitoris. and veins innumerable. Its nerves are chiefly derived from the intercostal, and its arteries and veins from the hypogastric and hemorrhoidal. The membrane which lines its cervix, is a continuation of the inner membrane of the vagina; but the outer surface of the body of the uterus is covered with the peritoneum, which is reflected over it, and descends from thence to the intestinum rectum. This duplicature of the peritoneum, by passing off from the sides of the uterus to the sides of the pelvis, is there firmly connected, and forms what are called ligamenta uteri latae, which serve not only to support the uterus, but to convey nerves and blood-vessels to it.

k, The ligamenta uteri rotunda arise from the sides of the fundus uteri, and passing along within the forepart of the ligamenta lata, descend through the abdominal rings, and terminate in the substance of the mons veneris. The substance of these ligaments is vascular: and although both they and the ligamenta lata admit the uterus, in the virgin state, to move only about an inch up and down; yet in the course of pregnancy they admit of considerable dilatation, and after parturition return nearly to their original state with surprising quickness.

l, On each side of the inner surface of the uterus, in the angle near the fundus, a small orifice is to be discovered, which is the beginning of one of the tubes fallopianae. Each of these tubes, which are two in number, passing through the substance of the uterus, is extended along the broad ligaments, till it reaches the edge of the pelvis, from whence it reflects back; and turning over behind the ligaments, about an inch of its extremity is seen hanging loose in the pelvis, near the ovarium. These extremities have a jagged appearance, are called fimbriae or morfia diaboli. Each tube fallopiana is usually about three inches long. Their cavities are at first very small, but become gradually larger, like a trumpet, as they approach the fimbriae.

m, Near the fimbriae of each tube fallopiana, about an inch from the uterus, is situated an oval body called ovarium, of about half the size of the male testicle. Each of these ovaria is covered by a production of the peritoneum, and hangs loose in the pelvis. They are of a flat and angular form; and appear to be composed of a white and cellular substance, in which we are able to discover several minute vesicles filled with a coagulable lymph, of an uncertain number, but not often exceeding twelve in each ovary. In the female of ripe years, these vesicles become exceedingly turgid; and a kind of yellow coagulum is gradually formed within one of them, which increases till its coat disappears; and it then changes into an hemispherical body, called corpus luteum, which resembles a bunch of currants, and is described as being hollow, and containing within its cavity the very minute membranes or eggs, each of which may become the seat of a fetus. In conception *, one of these mature ova is supposed to be impregnated with the male semen, and to be squeezed out of its nidus into the fallopian tube; and Baron Haller observes, that the number of scars or fissures in the ovarium constantly corresponds with the number of fetuses excluded by the mother.

PART V. OF THE THORAX.

a, The thorax, or chest, is that cavity of the trunk which extends from the clavicles, or lower part of the neck, to the diaphragm; and includes the vital organs, which are the heart and lungs; and likewise the trachea and oesophagus. This cavity is formed by the ribs and vertebrae of the back, covered by a great number of muscles, and by the common integuments, and anteriorly by two glandular bodies called the breasts. The spaces between the ribs are filled up by muscular fibres, which from their situation are called intercostal muscles.

CHAP. I.

Of the Breasts (b).

a, The breasts may be defined to be two large conglomerate glands mixed with a good deal of adipose membrane. The glandular part is composed of an infinite number of minute arteries, veins, and nerves.

b, The arteries are derived from two different trunks; one of which is called the internal, and the other the external mammary artery. The first of these arises from the subclavian, and the latter from the axillary.

c, The veins everywhere accompany the arteries, and are distinguished by the same name. The nerves are chiefly from the vertebral pairs. Like all other conglomerate glands, the breasts are made up of a great many small distinct glands, in which the milk is secreted from the ultimate branches of arteries. The excretory ducts of these several glands, gradually uniting as they approach the nipple, form the tubuli lactiferi, which are usually about seven or eight in number, and open at its apex. These ducts, in their course from the glands, are surrounded by a ligamentary elastic substance, which terminates with them in the nipple. Both this substance, and the ducts which it contains, are capable of considerable extension and contraction; but in their natural state are moderately corrugated, so as to prevent an involuntary flow of milk, unless the distending force be very great, from the accumulation of too great a quantity.

d, The whole substance of the nipple is very spongy and elastic; its external surface is uneven, and full of small tubercles. The nipple is surrounded with a disc or circle of a different colour, called the areola; and on the inside of the skin, under the areola, are many sebaceous glands, which pour out a mucus to defend the areola and nipple; for the skin upon these parts is very thin, and the nervous papillae lying very bare are much exposed to irritation.

e, The breasts are formed for the secretion of milk, which is destined for the nourishment of the child for some time after its birth. This secretion begins to take place soon after delivery, and continues to flow for

(b) What is here said is to be considered as being applicable only to the female breasts, those of the male subject not seeming to need a particular description. many months in very large quantities, if the woman suckles her child.

f. The operation of suction depends on the principles of the air-pump, and the flow of milk through the lactiferous tubes is facilitated by their being stretched out.

g. The milk, in its properties, seems to resemble the chyle. It appears to be composed of oil, mucilage; and water, with a considerable quantity of sugar; and, like the chyle, frequently retains the nature of the aliments and medicines taken into the stomach.

**CHAP. II.**

**Of the Pleura.**

a. The cavity of the thorax is everywhere lined by a membrane of a firm texture, called pleura. It is composed of two distinct portions or bags, which, by being applied to each other laterally, form a septum called mediastinum; which divides the cavity into two parts; and is attached to the vertebrae of the back behind, and before to the sternum. But the two laminae of which this septum is formed, do not everywhere adhere to each other: for at the lower part of the thorax they are separated, to afford a lodgement to the heart; and at the upper part of the cavity they receive between them the thymus.

b. The pleura is plentifully supplied with arteries and veins from the intercostals; and its nerves are derived from the vertebral pairs. This membrane is exceedingly sensible; and it is to this sensibility we owe the painful stitch we sometimes feel in the side, and which, when in a certain degree, constitutes a very acute disease, called the pleurisy, which is occasioned by an inflammation of this membrane.

c. The inner surface of the pleura is smooth; and, like all the other cavities, is constantly moistened by the lymph (c).

d. The mediastinum (p), by dividing the breast into two cavities, obviates many inconveniences to which we should otherwise be liable. It prevents the two lobes of the lungs from compressing each other when we lie on one side; and consequently contributes to the freedom of respiration, which is disturbed by the least pressure on the lungs. If the point of a sword penetrates between the ribs into the cavity of the thorax, the lungs on that side cease to perform their office; because the air being admitted through the wound, prevents the dilatation of that lobe; while the other lobe, which is separated from it by the mediastinum, remains unhurt, and continues to perform its function as usual.

**CHAP. III.**

**Of the Thymus.**

a. The thymus is a glandular substance, the use of which is not yet perfectly ascertained. It is of an oblong figure; and is larger in the fetus and in young children than in adults; being sometimes nearly effaced

(c) When this fluid is exhaled in too great a quantity, or is not properly carried off, it accumulates and constitutes the hydrops pelvis.

(d) Sometimes matter collects between the two laminae of the mediastinum; and surgical authors, in such cases, direct to trepan the sternum. But the disease does not seem often to occur; and when it does happen, cannot be distinguished with certainty. In a patient who died of that disorder of the breast named by Dr Heberden angina pectoris, Dr Haygarth of Chester, found a collection of what appeared to be pus, between these laminae, which had occasioned sudden death by breaking into the trachea, and thus producing suffocation.

**CHAP. IV.**

**Of the Diaphragm.**

a. The cavity of the thorax is separated from that of the abdomen, by a fleshy and membranous septum called the diaphragm or midriff. The greatest part of it is composed of muscular fibres; and, on this account, systematic writers usually place it very properly among the muscles. Its middle part is tendinous; and it is covered by the pleura above, and by the peritoneum below. It seems to have been improperly named septum transversum; as it does not make a plain transverse division of the two cavities, but forms a kind of vault, the fore-part of which is attached to the sternum. Laterally it is fixed to the half of the true ribs, and to all the false ribs; and its lower and posterior part is attached to the vertebrae lumbarum, where it may be said to be divided into two portions or crura.

b. The principal arteries of the diaphragm are derived from the aorta; and its veins pass into the vena cava. Its nerves are chiefly derived from the cervical pairs. It affords a passage to the vena cava through its tendinous part, and to the oesophagus through its fleshy portion. The aorta passes down behind it, between its crura.

c. The diaphragm not only serves to divide the thorax from the abdomen, but by its muscular structure is rendered one of the chief agents in respiration. When its fibres contract, its convex side, which is turned towards the thorax, becomes gradually flat, and, by increasing the cavity of the breast, affords room for a complete dilatation of the lungs, by means of the air which is then drawn into them by the act of inspiration. The fibres of the diaphragm then relax; and as it resumes its former state, the cavity of the thorax becomes gradually diminished, and the air is driven out again from the lungs by a motion contrary to the former one, called expiration.

d. It is in some measure by means of the diaphragm that we void the faeces at the anus, and empty the urinary bladder. Besides these offices, the acts of coughing, sneezing, speaking, laughing, gaping, and fighting, could not take place without its assistance; and the gentle pressure, which all the abdominal viscera receive from its constant and regular motion, cannot fail to assist in the performance of the several functions which were ascribed to those viscera.

**CHAP. V.**

**Of the Trachea.**

a. The trachea, or windpipe, is a cartilaginous and membranous canal, through which the air passes into the lungs. Its upper part, which is called the larynx, is composed of five cartilages. The uppermost and smallest of these cartilages is placed over the glottis or mouth of the larynx, and is called epiglottis; which has been before spoken of, as closing the passage to the lungs in the act of swallowing. The sides of the larynx are composed of the arytenoid cartilages, which are of a very complex figure, not easy to be described. The anterior and larger part of the larynx is made up of two cartilages; one of which is called thyroid, or lamelliform, from its being shaped like a buckler; and the other cricoid, or annularis, from its resembling a ring. Both these cartilages may be felt immediately under the skin, in the fore-part of the throat; and the thyroid, by its convexity, forms an eminence called promontorium, which is usually more considerable in the male than in the female subject.

b. All these cartilages are united to each other by means of very elastic, ligamentous fibres; and are enabled, by the assistance of several muscles, to dilate or contract the passage of the larynx, and to perform that variety of motion which seems to point out the larynx as being the principal organ of the voice; for when the air passes out through a wound in the trachea, it produces no sound.

c. These cartilages are moistened by a mucus, which seems to be secreted by minute glands situated near them. The upper part of the trachea, and the cri- coid and thyroid cartilages, are in some measure covered anteriorly by a considerable body, which is supposed to be of a glandular structure, and from its situation is called the thyroid gland; though its excretory duct has not yet been discovered, or its real use ascertained.

d. The inside of the glottis is covered by a very fine membrane, which is moistened by a constant supply of watery lymph. From the larynx, the canal begins to take the name of trachea, or afferent arteria; and extends from thence as far down as the fourth or fifth vertebra of the back, where it divides into two branches, which are the right and left bronchial tube. Each of these bronchi ramifies through the substance of that lobe of the lungs, to which it is distributed, by an infinite number of branches, which are formed of cartilages separated from each other, like those of the trachea, by an intervening membranous and ligamentary substance. Each of these cartilages is of an angular figure; and as they become gradually less and less in their diameter, the lower ones are in some measure received into those above them, when the lungs, after being inflated, gradually collapse by the air being pushed out from them in expiration. As the branches of the bronchi become more minute, their cartilages become more and more angular and membranous, till at length they are found to be perfectly membranous, and at last become invisible.

e. The trachea is furnished with fleshy or muscular fibres, some of which pass through its whole extent longitudinally, while the others are carried round it in a circular direction; so that, by the contraction or relaxation of these fibres, it is enabled to shorten or lengthen itself, and likewise to dilate or contract the diameter of its passage.

f. The trachea, and the bronchi, in all their ramifications, are furnished with very minute glands, which discharge a pellucid lymph on the inner surface of these tubes.

g. The trachea appears to be formed with infinite wisdom for the uses it is intended to serve. Its cartilages, by keeping it constantly open, afford a free passage to the air, which we are obliged to be incessantly respiring; and its membranous part, by being capable of contraction and dilatation, enables us to receive and expel the air in a greater or less quantity, and with more or less velocity, as may be required in singing or in declamation.

h. The generality of anatomists describe the trachea as being simply membranous at its posterior part, that it may give way to the aliment as it descends through the oesophagus, and not impede its passage; as it would be liable to do, if the trachea was cartilaginous here, as it is in the sides and fore-part (x). But there are arguments brought to prove that this is not its use; and these are, That the oesophagus, as Mr Windlow observes, does not descend immediately behind it, but somewhat laterally to the left; that the bronchi, at their upper part, are likewise simply membranous posteriorly where the oesophagus no longer accompanies them; and that it would perhaps be dangerous if the trachea was permitted to give way to the aliment in its descent; as the respiration would be by this means impeded, and this function seems to be too essential to life to be exposed to any such interruption.

i. The trachea receives its arteries from the carotids, and its veins pass into the jugulars; its nerves arise from the recurrent and from the cervical plexus.

**CHAP. VI.**

**Of the Lungs.**

a. The lungs fill the greater part of the cavity of the breast. They are of a soft and spongy texture; and are divided into two lobes, which are separated from each other by the mediastinum, and are externally covered by a production of the pleura. Each of these is divided into two or three lesser lobes; and we commonly find three in the right side of the cavity, and two in the left.

b. To discover the structure of the lungs, it is required to follow the ramifications of the bronchi, which were described in the last section. These becoming gradually more and more minute, at length terminate in the cellular spaces or vesicles, which make up the greatest part of the substance of the lungs, and readily communicate with each other.

c. The mucous, which was mentioned as passing into the bronchi, constitutes what we expectorate; and the most frequent cause of cough, seems to depend on the abundance or the tenacity of this secretion. Everything we throw off by hawking or spitting, is derived either from the lungs, the nostrils, or the salivary glands; and, on the contrary, all that we bring up by vomiting comes from the stomach.

d. The lungs receive nerves from the intercostals, but chiefly

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(x) The first of these opinions appears now to be the most generally adopted; for although the membranous structure of the trachea and bronchi may assist in shortening the canal, yet it seems likewise to assist in the descent of the food. chiefly from the eighth pair or par vagum. This last pair, having reached the thorax, sends off a branch on each side of the trachea, called the recurrent; which re-ascend, and go to distribute themselves to the larynx and its muscles, and likewise to the oesophagus.

e. There are two series of arteries which carry blood to the lungs: these are the arteriae bronchiales Ruyshii, and the pulmonary artery.

f. The arteriae bronchiales begin usually by two branches; one of which commonly arises from the intercostal, and the other from the trunk of the aorta: but sometimes there are three of these arteries, and in some subjects only one. The use of these arteries is to serve for the nourishment of the lungs, and their ramifications are seen creeping everywhere on the branches of the bronchi. The blood is brought back from them by the bronchial vein into the vena azygos.

g. The pulmonary artery and vein are not intended for the nourishment of the lungs; but the blood in its passage through them is destined to undergo some changes, or to acquire certain essential properties (probably from the action of the air), which it has lost in its circulation through the other parts of the body. The pulmonary artery receives the blood from the right ventricle of the heart; and dividing into two branches, accompanies the bronchi everywhere, by its ramifications through the lungs; and the blood is afterwards conveyed back by the pulmonary vein, which gradually forming a considerable trunk, goes to empty itself into the left ventricle of the heart; so that the quantity of blood which enters into the lungs, is perhaps greater than that which is sent in the same proportion of time, through all the other parts of the body.

CHAP. X.

Of the Pericardium, and of the Heart and its Auricles.

a. The two membranous bags of the pleura, which were described as forming the mediastinum, recede one from the other, so as to form a complete sac, in which the heart is securely lodged; and this sac is the pericardium (a), which appears to be composed of two tunics, united to each other by cellular membrane: the outer coat is a production of the mediastinum; and the inner tunic appears to adhere to the great vessels of the heart, on which it gradually disappears.

b. This bag is attached to the tendinous part of the diaphragm, and contains a coagulable lymph, the liquor pericardii, which serves to lubricate the heart and facilitate its motions, and is probably secreted and absorbed in the same manner as it is in the other cavities of the body.

c. The arteries of the pericardium are derived from the phrenic, and its veins pass into veins of the same name; its nerves are likewise branches of the phrenic.

d. The size of the pericardium is adapted to that of the heart, being usually large enough to contain it loosely. As its cavity does not extend to the sternum, the lungs cover it in inspiration; and as it every where invests the heart, it effectually secures it from being injured by lymph, pus, or any other fluid, extravasated into the cavities of the thorax.

a. The heart is a hollow muscle of a conical shape, situated transversely between the two laminae of the mediastinum, at the lower part of the thorax; having its basis turned towards the right side, and its point or apex towards the left. Its lower surface is somewhat flattened where it is attached to the diaphragm. Its basis, from which the great vessels originate, is covered with fat; and has two hollow and fleshy appendages, called the auricles. Round these several openings, the heart seems to be of a firm, ligamentous texture, from which all its fibres seem to originate; and as they advance from thence towards the apex, the substance of the heart seems to become thinner.

b. The heart includes two cavities, or ventricles, which are separated from each other by a fleshy septum: one of these is called the right, and the other the left ventricle; though perhaps with respect to their situation, it would be more proper to distinguish them into the anterior and posterior ventricles.

c. The outside of the heart is covered by a very fine membrane; and its structure is perfectly muscular or fleshy, being composed of fibres which are described as passing in different directions; some as being extended longitudinally from the basis to the apex; others, as taking an oblique or spiral course; and a third sort, as being placed in a transverse direction. Within the two ventricles we observe several furrows, and there are likewise tendinous strings, which arise from fleshy columns in the two cavities, and are attached to the valves of auricles. That the use of these and of the other valves of the heart may be understood, it must be observed, that four large vessels pass out from the basis of the heart, viz. two arteries and two veins; and that each of these vessels is furnished with a thin membranous production, which is attached all round to the borders of their several orifices, from whence hanging loosely down, they appear to be divided into two or three distinct portions. But as their uses in the arteries and veins are different, so are they differently disposed. Those of the arteries are intended to give way to the passage of the blood into them from the ventricles, but to oppose its return: and on the contrary, the valves of the veins are constructed so as to allow the blood only to pass into the heart. In consequence of these different uses, we find the valves of the pulmonary artery and of the aorta attached to the orifices of those vessels, so as to have their concave surfaces turned towards the artery; and their convex surfaces, which mutually meet together, being placed towards the ventricle, only permit the blood to pass one way, which is into the arteries. There are usually three of these valves belonging to the pulmonary artery, and as many to the aorta, and from their figure they are called valvulae semilunares. The communication between the two great veins and the ventricles, is by means of the two appendages or auricles into which the blood is discharged; so that the other valves, which may be said to belong to the veins, are placed in each ventricle, where the auricle opens into it. The valves

(r) The pericardium, though placed between the two laminae of the mediastinum, appears to be a distinct bag, very different in its structure from the pleura, being of a firm and somewhat tendinous complexion. in the right ventricle are usually three in number, and are named *valvula tricuspidis*; but in the left ventricle we commonly observe only two, and these are the *valvula mitralis*. The membranes which form these valves in each cavity are attached so as to project somewhat forward; and both the *tricuspidis* and the *mitrales* are connected with the tendinous strings which were described as arising from the flebly *columnae*. By the contraction of either ventricle, the blood is driven into the artery which communicates with that ventricle; and these tendinous strings being gradually relaxed, as the sides of the cavity are brought nearer to each other, the valves naturally close the opening into the auricle, and the blood necessarily directs its course into the then only open passage, which is into the artery: but after this contraction, the heart becomes relaxed; the tendinous strings are again stretched out; and drawing the valves of the auricle downwards, the blood is poured by the veins into the ventricle; from whence, by another contraction, it is again thrown into the artery, as will be described hereafter. The right ventricle is not quite so long, though somewhat larger than the left, but the latter has more substance than the other; and this seems to be because it is intended to transmit the blood to the most distant parts of the body, whereas the right ventricle distributes it only to the lungs.

d. The heart receives its nerves from the par vagum and the intercostals. The arteries which serve for its nourishment are two in number, and arise from the aorta. They surround in some measure the basis of the heart, and from this course are called the *coronary arteries*. From these arteries the blood is returned by veins of the same name into the auricles, and even into the ventricles.

c. The muscular bags called the *auricles* are situated at the basis of the heart, by the sides of each other; and, corresponding with the two ventricles, are, like those two cavities, distinguished into right and left. These sacs, which are interiorly unequal, have externally a jagged appendix, which, from its having been compared to the extremity of an ear, has given them their name of *auricles*.

**CHAP. XI.**

**Description of the Blood-vessels.**

a. The heart has been described as contracting itself, and throwing the blood from its two ventricles into the pulmonary artery and the aorta; and then as relaxing itself, and receiving a fresh supply from two large veins, which are the pulmonary veins, and the vena cava. We will now point out the principal distributions of these vessels.

b. The pulmonary artery arises from the right ventricle by a large trunk, which soon divides into two considerable branches, which pass to the right and left lobes of the lungs: each of these branches is afterwards divided and subdivided into an infinite number of branches and ramifications, which extend through the whole substance of the lungs; and from these branches the blood is returned by the veins, which, contrary to the course of the arteries, begin by very minute canals, and gradually become larger, forming at length four large trunks called the *pulmonary veins*, which terminate in the left auricle by one common opening, from whence the blood passes into the left ventricle. From this same ventricle arises the *aorta* or great artery, which at its beginning is nearly an inch in diameter. It soon sends off two branches, the *coronaries*, which go to be distributed to the heart and its auricles. After this, at or about the third or fourth vertebra of the back, it makes a considerable curvature. From this curvature (o) arise three arteries; one of which soon divides into two branches. The first two are the left subclavian, and the left carotid; and the third is a common trunk to the right subclavian and right carotid; though sometimes both the carotids arise distinctly from the aorta.

c. The two *carotids* ascend within the subclavians, along the sides of the trachea; and when they have reached the larynx, divide into two principal branches the *internal* and *external carotid*. The first of these runs a little way backwards in a bending direction; and, having reached the under part of the ear, passes through the canal in the os petrosum, and entering into the cavity of the cranium is distributed to the brain and the membranes which envelop it. The *external carotid* divides into several branches, which are distributed to the larynx, pharynx, and other parts of the neck, and to the jaws, lips, tongue, eyes, temples, and all the external parts of the head.

d. Each *subclavian* is likewise divided into a great number of branches. It sends off the *vertebral artery*, which passes through the openings we see at the bottom of the transverse processes of the vertebrae of the neck, and in its course sends off many ramifications to the neighbouring parts. Some of its branches are distributed to the spinal marrow; and, after a considerable inflection, it enters into the cranium, and is distributed to the brain. The *subclavian* likewise sends off branches to the muscles of the neck and scapula; and the mediastinum, thymus, pericardium, diaphragm, the breasts, and the muscles of the thorax, and even of the abdomen, derive branches from the subclavian; which are distinguished by different names, alluding to the parts to which they are distributed, as the mammary, the phrenic, the intercostal, &c. But notwithstanding the great number of branches which have been described as arising from the subclavian, it is still a considerable artery when it reaches the *axilla*, where it drops its former name, which alluded to its passage under the clavicle, and is called the *axillary artery*; from which a variety of branches are distributed to the muscles of the breast, scapula, and arm. But its main trunk taking the name of *brachialis*, runs along within side the arm near the os humeri, till it reaches the joint of the fore-arm, and then it divides into two branches. This division, however, is different in different subjects; for in some it takes place higher up, and in others lower down. When it happens to divide above the joint, it may be considered as a happy disposition in case of an accident by bleeding; for supposing the artery to be unfortunately punctured by the lancet,

(c) Anatomists usually call the upper part of this curvature, *aorta ascendens*; and the other part of the artery to its division at the iliacs, *aorta descendens*: but they differ about the place where this distinction is to be introduced; and it seems sufficiently to answer every purpose, to speak only of the aorta and its curvature. lancet, and that the hemorrhage could only be stopt by making a ligature on the vessel, one branch would remain unhurt, through which the blood would pass uninterrupted to the fore arm and hand. One of the two branches of the brachialis plunges down under the flexor muscles, and runs along the edge of the ulna; while the other is carried along the outer surface of the radius, and is easily felt at the wrist, where it is only covered by the common integuments. Both these branches commonly unite in the palm of the hand, and form an arterial arch from whence branches are detached to the fingers.

e. The aorta, after having given off at its curvature the carotids and subclavians, which convey blood to all the upper parts of the body, descends upon the bodies of the vertebrae a little to the left, as far as the os sacrum, where it drops the name of aorta, and divides into two considerable branches. In this course, from its curvature to its bifurcation, it sends off several arteries, in the following order.

f. 1. Two little arteries, and sometimes only one, first demonstrated by Ruysh as going to the bronchi, and called arteriae bronchiales Ruyshii. 2. The inferior, intercostal arteries which are distributed between the ribs in the same manner as the arteries of the three or four superior ribs are, which are derived from the subclavian. These arteries send off branches to the medulla spinalis. 3. The phrenic, which goes to the diaphragm, and the arteries which are distributed to the oesophagus. 4. The celiac, which arises from the aorta, under the diaphragm, and is distributed to the stomach, omentum, duodenum, pancreas, spleen, liver, and gall-bladder. 5. The superior mesenteric artery, which is distributed to the mesentery and small intestines. 6. The renal, which go to the kidneys. 7. The arteries which are distributed to the glandula renalis. 8. The spermatic. 9. The inferior mesenteric artery, which ramifies through the lower portion of the mesentery and the large intestines. A branch of this artery which goes to the rectum is called the internal hemorrhoidal. 10. The lumbar arteries, and a very small branch called the facia; which are distributed to the muscles of the loins and abdomen, and to the os sacrum and medulla spinalis.

g. The trunk of the aorta, when it has reached the last vertebra lumborum, or the os sacrum, drops the name of aorta, and separates into two forked branches, called the iliacs. Each of these soon divides into two branches; one of which is called the internal iliac, or hypogastric artery; and is distributed to the urinary bladder, intestine rectum, and the neighbouring parts. That branch which goes to the rectum is called the external hemorrhoidal. The external iliac, after having given off the umbilical artery, and the epigastric, which is distributed to the recti muscles, passes out of the abdomen, under Poupart's ligament, and takes the name of crural artery. It descends on the inner part of the thigh close to the os femoris, sending off branches to the muscles; and then sinking deeper in the hind part of the thigh, reaches the ham, where it takes the name of popliteal. After this it separates into two considerable branches; one of which is called the anterior tibial artery; the other divides into two branches; and these arteries all go to be distributed to the leg and foot.

h. The blood, which is thus distributed by the aorta to all parts of the body, is brought back by the veins, which are supposed to be continued from the ultimate branches of arteries, and, uniting together as they approach the heart, at length form two large trunks, the vena cava ascendens and vena cava descendens.

i. All the veins which bring back the blood from the upper extremities, and from the head and breast, pass into the vena cava descendens; those which return it from the lower parts of the body, terminate in the vena cava ascendens; and these two cavas, uniting together as they approach the heart, open by one common orifice into the left auricle.

k. It does not here seem to be necessary to follow the different divisions of the veins as we did those of the arteries; and it will be sufficient to remark, that, in general, every artery is accompanied by its vein, and that both are distinguished by the same name. But like many other general rules, this too has its exceptions (n). The veins, for instance, which accompany the external and internal carotid, are not called the carotid veins, but the external and internal jugular. In the thorax there is a vein distinguished by a proper name, and this is the axigos or vena sine pari. This vein, which is a pretty considerable one, runs along by the right side of the vertebrae of the back, and is chiefly destined to receive the blood from the intercostals on that side, and to convey it into the vena cava descendens. In the abdomen, we meet with a vein which is still a more remarkable one; and this is the vena porta, which performs the office both of an artery and a vein. It is formed by a reunion of all the veins which come from the stomach, intestines, omentum, pancreas, and spleen, so as to compose one great trunk, which goes to ramify through the liver; and after having deposited the bile, its ramifications unite and bring back into the vena cava, not only the blood which the vena porta had carried into the liver, but likewise the blood from the hepatic artery. Every artery has a vein which corresponds with it; but the trunks and branches of the veins are more numerous than those of the arteries. The reasons for this disposition are perhaps not difficult to be explained. The blood, in its course through the veins, is much farther removed from the source and cause of its motion which are in the heart, than it was when in the arteries: so that its course is consequently less rapid, and enough of it could not possibly be brought back to the heart, in the moment of its dilatation, to equal the quantity which is driven into the arteries from the two ventricles at the time they contract; and the equilibrium, which is so essential to the continuance of life and health, would consequently be destroyed if the capacity of the veins did not exceed that of the arteries, in the same proportion that the rapidity of the blood's motion through the arteries exceeds that of its return through the veins.

l. A large artery ramifying through the body, and continued to the minute branches of veins, which gradually unite together to form a large trunk, may be compared to two trees united to each other at their tops; or rather as having their ramifications so disposed, that the two trunks terminate in one common point: and if

(n) In the extremities, some of the deep seated veins, and all the superficial ones, take a course different from that of the arteries. if we farther suppose that both these trunks and their branches are hollow, and that a fluid is incessantly circulated through them, by entering into one of the trunks and returning through the other, we shall be enabled to conceive how the blood is circulated thro' the vessels of the human body.

m, Every trunk of an artery, before it divides, is nearly cylindrical, or of equal diameter thro' its whole length; and so are all its branches when examined separately. But every trunk seems to contain less blood than the many branches do into which that trunk separates; and each of these branches probably contains less blood than the ramifications do into which it is subdivided: And it is the same with the veins; the volume of their several ramifications, when considered together, being found to exceed that of the great trunk which they form by their union.

n, The return of the blood through the veins to the heart is promoted by the action of the muscles and the pulsation of the arteries. This return is likewise greatly assisted by the valves which are to be met with in the veins, and which constitute one of the great distinctions between them and the arteries. These valves (1), which are supposed to be formed by the inner coat of the veins, permit the blood to flow from the extremities towards the heart, but oppose its return.

o, Both the arteries and veins are membranous canals which are composed of three tunics (k); and even the most minute branches of both these series of vessels are nourished by still more minute arteries and veins, which are seen creeping over their coats, and ramifying through their whole substance, and are called vasa rerum: they have likewise many minute branches of nerves.

p, The arteries are much stronger than the veins; and they seem to require this force to be enabled to resist the impetus with which the blood circulates thro' them, and to impel it on towards the veins.

q, When the heart contracts, it impels the blood into the arteries, and sensibly distends them; and these vessels again contract, as the heart becomes relaxed to receive more blood from the auricles. So that the cause of the contraction and dilatation of the arteries, seems to be easy to be understood, being greatly dependent on the motion of the heart: but in the veins, where the effects of this impulse are not so sensibly felt, the blood seems to flow in a constant and equal stream; and this, together with its pulsing gradually from a small channel into a larger one, seems to be the reason why the veins have no pulsatory motion (2).

CHAP. XII. Of the Action of the Heart, Auricles, and Arteries.

a, The heart, at the time it contracts, drives the blood from its ventricles into the arteries; and the arteries, being thus filled and distended, are naturally inclined to contract, the moment the heart begins to dilate, and cease to supply them with blood. These alternate motions of contraction and dilatation of the heart and arteries are distinguished by the names of systole and diastole. When the heart is in a state of contraction or systole, the arteries are at that instant distended with blood and in their diastole; and it is in this state we feel their pulsatory motion, which we call the pulse. When the heart dilates, and the arteries contract, the blood is impelled onwards into the veins, thro' which it is returned back into the heart. While the heart, however, is in its systole, the blood cannot pass from the veins into the ventricles; but is detained in the auricles, which are two reservoirs formed for this use, till the diastole or dilatation of the heart takes place; and then the distended auricles contract, and drive the blood into the ventricles: so that the auricles have an alternate systole and diastole, as well as the heart.

b, Although both the ventricles of the heart contract at the same time, yet the blood passes from one to the other. In the same moment, for instance, that the left ventricle drives the blood into the aorta, the right ventricle impels it into the pulmonary artery, which is distributed through all the substance of the lungs. The blood is afterwards brought back into the left ventricle by the pulmonary vein, at the same time that the blood is returned by the cavae, into the right ventricle, from all the other parts of the body.

c, This seems to be the mode of action of the heart and its vessels; but the cause of this action, has like all other intricate and interwoven subjects, been differently explained; often with much ingenuity, though perhaps not yet with sufficient certainty to be established as a physical truth. It is probably occasioned by the influence of the nerves, excited in consequence of an impression made on the heart by the blood itself, which by its quantity and heat (m), or other properties (n), is perhaps capable of first exciting that motion,

(1) The valves are most frequent in the smaller veins. As the column of blood is increased, they seem to become less necessary; and, therefore in the vena cava ascendens we meet with only one valve, which is near its origin.

(2) There are writers who describe the arteries as having five tunics; while others speak only of four; and many will allow them only three; which are the nervous, muscular, and cuticular tunics. The veins are by many writers supposed to consist of the same number of coats as the arteries; but that, by being thinner, they do not easily admit of separation. That they have no muscular coat, however, seems now to be pretty generally allowed; and there are eminent anatomists who contend, (and seemingly with good reason), that no muscular fibres are to be demonstrated even in the coats of arteries.

(3) Many modern writers allow, that there is a pulsatory motion in the great veins near the heart; but it there seems to be occasioned by the motion of the diaphragm, and by the regurgitation of the blood in the cavae.

(4) Dr. Hales observed, that the pulse is quicker in small animals, than in large ones; and this seems to be, because their heat is proportionally greater. The velocity of the blood's motion seems likewise to depend on the greater or less degree of irritability of the body through which it circulates. In people of weak habits, it is constantly more rapid than in robust subjects. In newborn infants, the pulse usually beats 120. As we approach to old age, and the irritability of the body decreases, it gradually becomes slower; and in advanced life, is found to beat only 60, 50, or 40, and sometimes not so often, in a minute.

(5) Dr. Harvey long ago suggested, that the blood is possessed of a living principle; and Mr. J. Hunter has lately endeavoured to revive this doctrine, in support of which he has adduced many ingenious arguments. The subject is a curious one, and deserves to be prosecuted as an inquiry which cannot but be interesting to physiologists.

CHAP. XIII. Of the Circulation.

a. After what has been observed of the structure and action of the heart and its auricles, and likewise of the arteries and veins; there seem to be but very few arguments required to demonstrate the circulation of the blood, which has been long since established as a medical truth. This circulation may be defined to be a perpetual motion of the blood, in consequence of the action of the heart and arteries, which impel it thro' all the parts of the body, from whence it is brought back by the veins to the heart (o).

b. A very satisfactory proof of this circulation, and a proof easy to be understood, may be deduced from the different effects of pressure on an artery and a vein. If a ligature, for instance, is passed round an artery, the vessel swells considerably between the ligature and the heart; whereas, if we tie up a vein, it only becomes filled between the extremity and the ligature: and this is what we every day observe in bleeding. The ligature we pass round the arm on these occasions compresses the superficial veins; and, the return of the blood thro' them being impeded, they become distended. When the ligature is too loose, the veins are not sufficiently compressed, and the blood continues its progress towards the heart; and on the contrary, when it is made too tight, the arteries themselves become compressed, and the flow of blood through them being impeded, the veins cannot be distended.

c. Another phenomenon which effectually proves the circulation, is the loss of blood that every living animal sustains by opening only a single artery of a moderate size; for it continues to flow from the wounded vessel till the equilibrium is destroyed which is essential to life. This truth was not unknown to the ancients; and it seems strange that it did not lead them to a knowledge of the circulation, as it sufficiently proves that all the other vessels must communicate with that which is opened. Galen, who lived more than 1500 years ago, drew this conclusion from it; and if we farther observe, that he describes (after Erasistratus who flourished about 450 years before him) the several valves of the heart, and determines their disposition and use, it will appear wonderful, that a period of near 2000 years should afterwards elapse before the true course of the blood was ascertained. This discovery, for which we are indebted to the immortal Harvey, has thrown new lights on physiology and medicine, and constitutes one of the most important periods of anatomical history.

CHAP. XIV. Of the Nature of the Blood.

a. Blood recently drawn from a vein into a basin, would seem to be an homogeneous fluid of a red colour (p); but, when suffered to rest, it soon coagulates, and divides into two parts, which are distinguished by the names of crassamentum and serum. The crassamentum is the red coagulum, and the serum is the water in which it floats.

b. Each of these may be again separated into two others. For the crassamentum, by being repeatedly washed in warm water, gives out all its red globules; and what remains appears to be composed of the coagulable lymph (q), which is a gelatinous substance, capable of being hardened by fire till it becomes perfectly horny; and if we expose the serum to a certain degree of heat, part of it will be found to coagulate like the white of an egg, and there will remain a clear and limpid water, resembling urine both in its appearance and smell. The most remarkable property of the serum is its being pervious to the common air. See Air, no 48.

c. The serum and crassamentum differ in their proportion in different constitutions; in a strong person the crassamentum is in a greater proportion to the serum, than in a weak one; and the same difference is found to take place in diseases (*).

EXPLANATION OF PLATES XVII. XIX. XX.

Plate XVII. This plate represents the heart in situ, all the large arteries and veins, with some of the muscles, &c.

Muscles, &c.—Superior Extremity.—a, Masticator. b, Complexus. c, Digastricus. d, Os hyoides. e, Thyroid gland. f, Levator scapulae. g, Cucullaris. h, The clavicles cut. i, The deltoid muscle. k, Biceps.

(o) The motion of the blood, and its passage from the arteries into the veins, may be perceived, with the assistance of a microscope, in the tails of fishes and in frogs.

(p) The blood, as it flows through the arteries, is observed to be more florid than it is in the veins; and this redness seems to be acquired in its passage through the lungs.

(q) It may not be improper to observe, that till of late the coagulable lymph has been confounded with the serum of the blood, which contains a substance that is likewise coagulable though only when exposed to heat, or certain chemical substances, whereas the other coagulates spontaneously when exposed to the air or to rest.

(r) When the blood separates into serum and crassamentum, if the latter be covered with a crust of a whitish or buff colour, it has been usually considered as a certain proof of the blood's being in a state of too great vascularity. This appearance commonly taking place in inflammatory diseases, has long served to confirm the theory which affirms the cause of inflammations to lender and obstructions. But Dr Fordyce accounts in a different manner for the formation of the buff. He affirms, that when the action of the arteries is increased, the blood, instead of being more viscid, is on the contrary more fluid, than in the ordinary state, previous to inflammation: and that, in consequence of this, the coagulable lymph suffers the red globules, which are the heaviest part of the blood, to fall down to the bottom before it coagulates: so that the crassamentum is divided into two parts; one of which is found to consist of the coagulable lymph alone, (in this case termed the buff); and the other, partly of this and partly of the red globules. k, Biceps flexor cubiti cut. l, Coraco-brachialis. m, Triceps extensor cubiti. n, The heads of the pro- nator teres, flexor carpi radialis, and flexor digitorum soblimis, cut. o, The flexor carpi ulnaris, cut at its extremity. p, Flexor digitorum profundus. q, Supi- nator radii longus, cut at its extremity. r, Ligamen- tum carpi transversale. s, Extensors carpi radiales. t, Latissimus dorsi. u, Anterior edge of the serratus anticus major. v, v, The inferior part of the dia- phragm. w, w, Its anterior edge cut. x, x, The kid- neys. y, Transversus abdominis. z, Os ilium.

**INFERIOR EXTREMITY.—**

a, Ploas magnus. b, Iliacus internus. c, The fleshy origin of the tensor va- gini femoris. d, d, The osa pubis cut from each other. e, Musculus pectinicus cut from its origin. f, Short head of the triceps adductor femoris cut. g, The great head of the triceps. h, The long head cut. i, Vattus internus. k, Vattus externus. l, Crus. m, Gemellus. n, Soleus. o, Tibia. p, Peroneus longus. q, Pe- roneus brevis. r, Fibula.

**HEART AND BLOOD-VESSELS.—**

A, The heart, with the coronary arteries and veins. B, The right auricle of the heart. C, The aorta ascendens. D, The left subclavian artery. E, The left carotid artery. F, The common trunk which sends off the right subclavian and right carotid arteries. G, The carotis externa. H, Ar- teria facialis, which sends off the coronary arteries of the lips. I, Arteria temporalis profunda. K, Aor- ta descendens. L, L, The iliac arteries,—which fend off M M, The femoral or crural arteries. N, B, The other arteries in this figure have the same distribution as the veins of the same name:—And generally, in the anatomical plates, the description to be found on the one side, points out the same parts in the other. 1, The frontal vein. 2, The facial vein. 3, Vena temporalis profunda. 4, Vena occipitalis. 5, Vena jugularis externa. 6, Vena jugularis interna, covering the arteria carotis communis. 7, The valvular arch on the palm of the hand, which is formed by 8, the radial artery and vein, and 9, the ulnar artery and vein. 10, 10, Cephalic vein. 11, Basilic vein, that on the right side, cut. 12, Median vein. 13, The humeral vein, which, with the median, covers the humeral ar- tery. 14, 14, The external thoracic or mammary ar- teries and veins. 15, The axillary vein, covering the artery. 16, 16, The subclavian veins, which, with (6 6) the jugulars, form. 17, The vena cava supe- rior. 18, The cutaneous arch of veins on the fore-part of the foot. 19, The vena tibialis antica, covering the artery. 20, The vena profunda femoris, covering the artery. 21, The upper part of the vena saphena major. 22, The femoral vein. 23, 23, The iliac veins. 24, 24, Vena cava inferior. 25, 25, The renal veins covering the arteries. 26, 26, The diaphragma- tic veins.

**PLATE XIX.**

**FIGURE 1.** Shews the contents of the thorax and ab- domen in situ.

1, Top of the trachea, or wind-pipe. 2, 2, The in- ternal jugular veins. 3, 3, The subclavian veins. 4, The vena cava descendens. 5, The right auricle of the heart. 6, The right ventricle. 7, Part of the left ventricle. 8, The aorta ascendens. 9, The pulmo- nary artery. 10, The right lung, part of which is cut off to shew the great blood-vessefs. 11, The left lung entire. 12, 12, The anterior edge of the diaphragm. 13, 13, The two great lobes of the liver. 14, The li- gamentum rotundum. 15, The gall-bladder. 16, The stomach. 17, 17, The jejunum and ilium. 18, The spleen.

**FIG. 2.** Shews the organs subservient to the chylo- poietic viscera,—with those of urine and generation; 11, The under side of the two great lobes of the li- ver. 2, Lobulus Spigelii. 2, The ligamentum ro- tundum. 3, The gall-bladder. 4, The pancreas. 5, The spleen. 6, 6, The kidneys. 7, The aorta de- scendens. 8, Vena cava ascendens. 9, 9, The renal veins covering the arteries. 10, A probe under the spermatic vessels and a bit of the inferior mesenteric artery, and over the ureters. 11, 11, The ureters. 12, 12, The iliac arteries and veins. 13, The rectum intestinum. 14, The bladder of urine.

**FIG. 3.** Shews the chylopoietic viscera, and organs subservient to them, taken out of the body entire.

A A, The under side of the two great lobes of the liver. B, Ligamentum rotundum. C, The gall-blad- der. D, Ductus cysticus. E, Ductus hepaticus. F, Ductus communis choledochus. G, Vena porta- rum. H, Arteria hepatica. I I, The stomach. K K, Vena & arteriae gastro-epiploicae, dextra & sinistra. L L, Vena & arteriae coronariae ventriculi. M, The spleen. N N, Mesocolon, with its vessels. O O O, Intestinum colon. P, One of the ligaments of the colon, which is a bundle of longitudinal muscu- lar fibres. Q Q Q Q, Jejunum and ilium. R R, Sig- moid flexure of the colon with the ligament continued, and over S, The rectum intestinum. T T, Levatores ani. U, Sphincter ani. V, The place to which the prostate gland is connected. W, The anus.

**FIG. 4.** Shews the heart of a fetus at the full time, with the right auricle cut open to shew the foramen o- vale, or pallage between both auricles.

a, The right ventricle. b, The left ventricle. c c, The outer side of the right auricle stretched out. d d, The posterior side, which forms the anterior side of the septum. e, The foramen ovale, with the mem- brane or valve which covers the left side. f, Vena ca- va inferior passing through g, A portion of the dia- phragm.

**FIG. 5.** Shews the Heart and large vessels of a fetus at the full time.

a, The left ventricle. b, The right ventricle. c, A part of the right auricle. d, Left auricle. e e, The right branch of the pulmonary artery. f, Arteria pul- monalis. g g, The left branch of the pulmonary ar- tery, with a number of its larger branches dissected from the lungs. h, The canalis arteriosus. i, The arch of the aorta. k k, The aorta descendens. l, The left subclavian artery. m, The left carotid artery. n, The right carotid artery. o, The right subclavian artery. p, The origin of the right carotid and right subclavian arteries in one common trunk. q, The ve- na cava superior or descendens. r, The right com- mon subclavian vein. s, The left common subclavian vein.

N. B. All the parts described in this figure are to be found in the adult, except the canalis arteriosus. Plate XX.

Fig. 1. Represents the under and posterior side of the bladder of urine, &c. a, The bladder. b, The insertion of the ureters. c, The vasa deferentia, which convey the semen from the testicles to d, The vesiculae seminales,—and pass through e, The prostate gland, to discharge themselves into f, The beginning of the urethra.

Fig. 2. A transverse section of the penis. g, Corpora cavernosa penis. h, Corpus cavernosum urethrae. i, Urethra. k, Septum penis. l, The septum between the corpus cavernosum urethrae, and that of the penis.

Fig. 3. A longitudinal section of the penis. m, The corpora cavernosa penis, divided by o, The septum penis. n, The corpus cavernosum glandis, which is the continuation of that of the urethra.

Fig. 4. Represents the female organs of generation. a, That side of the uterus which is next the os sacrum. r, Its fundus. s, Its cervix. b, The Fallopian or uterine tubes, which open into the cavity of the uterus;—but the other end is open within the pelvis, and surrounded by c, The ligamenta. d, The ovaria. e, The os internum uteri, or mouth of the womb. f, The ligamenta rotunda, which passes without the belly, and is fixed to the labia pudendi. g, The cut edges of the ligamenta lata, which connects the uterus to the pelvis. h, The inside of the vagina. i, The orifice of the urethra. k, The clitoris surrounded by (l) the prepuce. m, The labia pudendi. n, The nymphae.

Fig. 5. Shews the spermatic ducts of the testicle filled with mercury. A, The vas deferens. B, Its beginning, which forms the posterior part of the epididymis. C, The middle of the epididymis, composed of serpentine ducts. D, The head or anterior part of the epididymis unravelled. e, The whole ducts which compose the head of the epididymis unravelled. f, The vasa deferentia. g, Rete testis. h, Some rectilinear ducts which send off the vasa deferentia. i, The substance of the testicle.

Fig. 6. The right testicle entire, and the epididymis filled with mercury. A, The beginning of the vas deferens. B, The vas deferens ascending towards the abdomen. C, The posterior part of the epididymis, named globus minor. D, The spermatic vessels inclosed in cellular substance. E, The body of the epididymis. F, Its head, named globus major. G, Its beginning from the testicle. H, The body of the testicle, inclosed in the tunica albuginea.

Chap. XV. Of the Glands and Secretions.

a, The glands are commonly understood to be small, roundish, or oval bodies, formed by the convolution of a great number of vessels, and destined to separate particular humours from the mass of blood.

b, They are usually divided into two classes. Of these, the fleshy and simple glands which are to be met with in different parts of the body, and are either solitary or in distinct clusters, are called conglomerate (t); and the pancreas, the parotids, and other compound glands, which are of a granulated substance, and appear to be composed of lesser glands, are called conglomerate.

c, The principal glands, and the humours they secrete, have been already described in different parts of this treatise; and there only remains for us to examine the general structure of the glands, and to explain the mechanism of secretion.

On the first of these subjects two different systems have been formed, each of which has had, and still continues to have, its adherents. One of these systems was advanced by Malpighi, who supposed that an artery, entering into a gland, ramifies very minutely through its whole substance; and that its branches ultimately terminate in a vesicular cavity or follicle, from whence the secreted fluid passes out through the excretory duct. This doctrine at first met with few opponents; but the celebrated Ruysh, who first attempted minute injections with wax, afterwards disputed the existence of these follicles; and asserted, that every gland appears to be a continued series of vessels, which, after being repeatedly convoluted in their course through its substance, at length terminate in the excretory duct: and this second system seems now to be the most generally adopted.

a, The mode of secretion has been explained in a variety of ways, and they are all perfectly hypothetical. In such an inquiry, it is natural to ask, how one gland constantly separates a particular humour, while another gland secretes one of a very different nature, from the blood? The bile, for instance, is separated by the liver, and the urine by the kidneys. Are these secretions to be imputed to any particular disposition in the fluids, or is their cause to be looked for in the solids?

b, It has been supposed, that every gland contains within itself a fermenting principle, by which it is enabled to change the nature of the blood it receives, and to endue it with a particular property. So that, according to this system, the blood, as it circulates thro' the kidneys, becomes mixed with the fermenting principle of those glands, and a part of it is converted into urine; and again, in the liver, in the salivary and other glands, the bile, the saliva, and other juices, are generated from a similar cause: but it seems to be impossible for any liquor to be confined in a place exposed to the circulation, without being carried away by the torrent of blood, every part of which would be equally affected; and this system of fermentation has long been rejected as vague and chimerical. But as the cause of secretion continued to be looked for in the fluids, the former system was succeeded by another, in which recourse was had to the analogy of the humours. It was observed,

(t) The lymphatic and mesenteric glands seem now to be considered as the only conglomerate glands, but their use has not yet been ascertained. The vessels which pour out mucus in different parts of the body are supposed to be simple follicles, or small cylindrical tubes, continued from the ends of arteries. The tonsils seem to be composed of many such simple follicles folded together, in one common covering, and opening into one common sinus. It has already been observed in a former note, that it is a subject of controversy how the liquor pericardii is secreted, and how the vapour which moistens the pleura and pericardium is exhaled into those cavities. served, that if paper is moistened with water, and oil and water are afterwards poured upon it, that the water only will be permitted to pass through it. But that, on the other hand, if the paper has been previously soaked in oil instead of water, the oil only, and not the water, will be filtered through it. These observations led to a supposition, that every secretory organ is originally furnished with a humour analogous to that which it is afterwards destined to separate from the blood; and that, in consequence of this disposition, the secretory vessels of the liver, for instance, will only admit the bilious particles of the blood, while all the other humours will be excluded. This system is an ingenious one, but the difficulties with which it abounds are unanswerable. For oil and water are immiscible; whereas the blood, as it is circulated through the body, appears to be an homogeneous fluid. Every oil will pass through a paper moistened only with one kind of oil; and wine or spirits mixed with water will easily be filtered through a paper previously soaked in water. Upon the same principle, all our humours, though differing in their other properties, yet agreeing in that of being perfectly miscible with each other, will all easily pass through the same filter. But there are not all the objections to this system. The humours which are supposed to be placed in the secretory vessels, for the determination of similar particles from the blood, must be originally separated without any analogous fluid; and that which happens once, may as easily happen always. Again, it sometimes happens, from a vicious disposi-

**Part VI. Of the Brain and its Integuments,**

**And**

**Of the Nerves.**

**Chap. I.**

**Of the Brain and its Integuments.**

The bones of the cranium were described, in the osteological part, as inclosing the brain, and defending it from external injury: but they are not its only protection; for when we make an horizontal section thro' these bones, we find this mass everywhere surrounded by two membranes (v), the dura and pia mater.

a, The first of these lines the interior surface of the cranium, to which it adheres strongly at the sutures, and at the many foramina through which vessels pass between it and the pericranium. The dura mater is perfectly smooth and inelastic; and its inner surface is constantly bedewed with a fine pellucid fluid, which every where separates it from the pia mater. The dura mater sends off several considerable processes, which divide the brain into separate portions, and prevent them from compressing each other. Of these processes there is one superior and longitudinal, called the falx or falceform process, from its resemblance to a fythe. It arises from the spine of the os frontis, near the critta galli, and extending along in the direction of the sagittal future, to beyond the lambdoidal future, divides the brain into two hemispheres. A little below the lambdoidal future, it divides into two broad wings or expansions, called the transverse or lateral processes, which prevent the lobes of the cerebrum from pressing on the cerebellum. Besides these there is a fourth, which is situated under the transverse processes, and, being continued to the spine of the occiput, divides the cerebellum into two lobes.

b, The blood, after being distributed through the cavity of the cranium by means of the arteries, is returned as in the other parts of the body by veins which all pass on to certain channels situated behind these several processes.

c, These canals or sinuses communicate with each other, and empty themselves into the internal jugular veins, which convey the blood into the vena cava. They are in fact triangular veins, and like the processes are distinguished into longitudinal and lateral; and where these three meet, and where the fourth passes off, we observe a fourth sinus, which is called torcular; Herophilus, who first described it, having supposed that the blood at the union of these two veins is as it were in a press. Within the sinuses we observe minute filaments, the chordae Willisis, which seem to add to their strength, and prevent their being too much dilated.

d, The pia mater is a much tenderer and finer membrane than the dura mater; being exceedingly delicate and vascular. It invests every part of the brain

(v) The Greeks call these membranes, meninges; but the Arabians, supposing them to be the source of all the other membranes of the body, afterwards gave them the names of dura and pia mater, by which they are now usually distinguished. and sends off an infinite number of elongations, which infiluate themselves between the convolutions, and even into the substance of the brain. This membrane is usually described as being composed of two laminae, of which the exterior one is named tunica arachnoides, from its supposed resemblance to a spider's web.

There are several parts included under the general denomination of brain. One of these, which is of the softest consistence, and fills the greatest part of the cavity of the cranium, is the cerebrum, or brain properly so called; another portion, which is seated in the inferior and posterior part of the head, is the cerebellum; and a third, which derives its origin from both these, is the medulla oblongata.

a. The cerebrum is a medullary mass of moderate consistence, filling up exactly all the superior part of the cavity of the cranium, and divided into two hemispheres by the falx of the dura mater. Each of these hemispheres is distinguished into an anterior, a middle and a posterior lobe. The first of these is lodged on the orbital processes of the os frontis; the middle lobes lie in the middle of the fossae of the basis of the cranium; and the posterior lobes are placed on the transverse septum of the os occipitis, immediately over the cerebellum, from which they are separated by the lateral processes of the dura mater.

b. The cerebrum appears to be composed of two distinct substances. Of these the exterior one, which is of a greyish or ash-colour, is called the cortex, and is somewhat softer than the other, which is very white, and is called medulla or substantia alba.

c. After having removed the falx, and separated the two hemispheres from each other, we perceive a white convex body, the corpus callosum, which is a portion of the medullary substance, uniting the two hemispheres to each other, and not invested by the cortex. By making an horizontal incision in the brain, on a level with this corpus callosum, we discover two oblong cavities, named the anterior or lateral ventricles, one in each hemisphere. These two ventricles, which communicate with each other posteriorly, are separated from each other throughout the greatest part of their extent, by a very fine medullary partition, called septum lucidum, from its delicacy and transparency. This septum is attached superiorly to a production of the corpus callosum, called the fornix. When we have removed this fornix, we discover several eminences, four pair of which follow each other very regularly; and these are the corpora striata, the thalami nervorum opticorum, and four others which Mr. Winslow has named tubercula quadrugemina. The corpora striata derive their name from their striated appearance, which seems to be occasioned by an intermixture of the cortical and medullary substances of the brain. The thalami nervorum opticorum are so called because the optic nerves arise chiefly from them; and they are likewise composed both of the cortex and medulla. The tubercula quadrugemina are four smaller eminences, situated behind the two other pair we just now described. The pineal gland, rendered so famous by Descartes, who supposed it to be the seat of the soul, is a small, soft, and oval body, about the size of a pea, situated behind the thalami, immediately above the tubercula. Under the thalami, we observe another cavity, which constitutes the third ventricle of the brain, and communicates with the anterior ventricles, with the glandula pituitaria, and likewise with the fourth ventricle. Its communication with the anterior ventricles is by means of a very narrow opening or rima, which extends from the anterior portion of the third ventricle, to the posterior portion of the two others, where they communicate with each other, and with the glandula pituitaria, by a canal, which from its form is called infundibulum. The glandula pituitaria is a soft and spongy body, placed upon the sella turcica. The third ventricle communicates with the fourth ventricle, which is placed between the cerebellum and medulla oblongata, by means of a groove or channel, which is the aqueductus Sylvii. The anterior ventricles, the thalami nervorum opticorum, the pineal gland, the tubercula quadrugemina, and other parts near these, are covered by an exceeding fine delicate and vascular membrane called plexus choroides.

The cerebellum, which is divided into two lobes, is of a more firm and compact substance than the cerebrum; but, like that, is composed of the cortical and medullary substances. From each side of the fourth ventricle of the brain, there arises a medullary trunk, which is distributed through the medullary substance of the cerebellum, by an infinite number of ramifications, which may be observed by making a vertical section of the cerebellum, where they constitute what is called arbor vitae. The reunion of the medullary substance of the cerebrum and cerebellum, at the basis of the cranium, forms the medulla oblongata, which extends to the great foramen of the occipital bone.

The medulla spinalis, which fills the vertebral canal from this foramen to the inferior portion of the os sacrum, is a continuation of the medulla oblongata, but with some little difference in its composition; the latter being altogether made up of the medullary substance; whereas the medulla spinalis appears to have its middle part composed of a brownish mass, resembling the cortical substance of the brain. The medulla spinalis is invested by a continuation of the membranes of the brain (v); and the pia mater, by sending off productions into its substance, affords a support to the blood-vessels as they ramify through it.

CHAP. II. Of the Nerves.

a. The nerves are white and glinting chords, differing from each other in size, colour, and consistence, and deriving their origin from the medulla oblongata and medulla spinalis. Anatomists describe forty pair of these nerves; ten of which originate from the medulla oblongata, and thirty from the medulla spinalis.

b. By carefully and gently elevating the brain from the basis of the cranium, we find the first ten pair arising in the following order: 1. The nervi olfactorii, distributed thro' the pituitary membrane, which constitutes the organ of smell. 2. The opticis, which go to the eyes, where they receive the impressions of visible

(v) The dissection of the brain requires considerable dexterity; and the reader, till he has seen such a dissection performed, will perhaps not be able to derive very clear ideas of its anatomy, from any description he can meet with of it in books. The uses of its several parts have never yet been ascertained. sible objects. 3. The oculorum motores so called, because they are distributed to the muscles of the eye.

4. The pathetici, distributed to the superior oblique muscles of the eyes, the motion of which is expressive of certain passions of the soul.

5. The nerves of this pair soon divide into three principal branches, and each of these has a different name. Its upper division is the ophthalmicus, which is distributed to various parts of the eyes, eye-lids, forehead, nose, and integuments of the face. The second is called the maxillaris superior, and the third maxillaris inferior, both which names allude to their distribution.

6. The adductores; each of these nerves is distributed to the abductor muscle of the eye, so called because it helps to draw the globe of the eye from the nose.

7. The auditorii (w), which are distributed through the organs of hearing.

8. The par vagum, which derives its name from the great number of parts to which it gives branches, both in the thorax and abdomen.

9. The linguales, or hypoglossi, which are distributed to the tongue, and appear to contribute both to the organ of taste, and to the motions of the tongue.

10. A pair which is distributed to the muscles of the head and neck.

c. It has been already observed, that the spinal marrow sends off thirty pair of nerves, and these are chiefly distributed to the exterior parts of the trunk, and to the extremities. They are commonly distinguished into the cervical, dorsal, lumbar, and sacral nerves. The cervical, which pass out from between the several vertebrae of the neck, are seven in number; the dorsal, twelve; the lumbar, five; and the sacral, five (x).

d. In the following course of the nerves both of the medulla oblongata and medulla spinalis, we observe, in many of them, irregular enlargements of their substance, which are called ganglia. These knots or tumours are not the effects of disease, but are to be met with in the same parts of the same nerves both in the fetus and the adult.

e. Some writers have considered them as so many little brains; and many other theories have been formed concerning them; none of which, however, have as yet led to ascertain their use.

f. The nerves, like the blood-vessels, in their course through the body, communicate with each other; and each of these communications constitutes what is called a plexus, from whence branches are again detached to different parts of the body. Some of these are constant, and considerable enough to be distinguished by particular names, as the femoral plexus, the pulmonary plexus, the hepatic, the cardiac, &c.

g. It would be foreign to the purpose of this article to follow the nerves through all their distributions; but it may be remembered, that, in describing the different viscera, mention was made of the nerves distributed to them. There is one pair, however, called the intercostal, or great sympathetic nerve; which seems to deserve a particular description, because it has an almost universal connection and correspondence with all the other nerves of the body. Authors are not perfectly agreed about the origin of the intercostal; but it may perhaps not improperly be described as beginning from filaments of the fifth and sixth pair; it then passes out of the cranium, through the bony canal of the carotid; from whence it descends laterally close to the bodies of the vertebrae, and receives branches from almost all the vertebral nerves; forming almost as many ganglia in its course through the thorax and abdomen. It sends off an infinite number of branches to the viscera in those cavities, and forms several plexus with the branches of the eighth pair or par vagum.

h. That the nerves are destined to convey the principles of motion and sensibility to the brain from all parts of the system, there can be no doubt; but how these effects are produced, no one has ever yet been able to determine. The inquiry has been a constant source of hypothesis in all ages; and has produced some ingenious ideas, and many erroneous positions, but without having hitherto afforded much satisfactory information.

i. The nerves appear to be perfectly inelastic, and are covered by the dura and pia mater; seeming to owe their firmness to the former of these tunics.

k. Some physiologists have considered a trunk of nerves as a solid cord, capable of being divided into an infinite number of filaments, by means of which the impressions of feeling are conveyed to the sensorium commune. Others have supposed it to be a canal, which afterwards separates into more minute channels; or, perhaps, as being an assemblage of many very small and distinct tubes, connected to each other, and thus forming a cylindrical cord. They who contend for their being solid bodies, are of opinion, that feeling is occasioned by vibration: so that, for instance, according to this system, by pricking the finger, a vibration would be occasioned in the nerve distributed through its substance; and the effects of this vibration, when extended to the sensorium, would be an excitant of pain. But the inelasticity, the softness, the connection, and the situation of the nerves, are so many proofs that vibration has no share in the cause of feeling.

l. Others have supposed, that in the brain and spinal marrow a very subtile fluid is secreted, and from thence conveyed through the imperceptible tubes which they consider as existing in the nerves. They have farther supposed, that this very subtile fluid, to which they have given the name of animal spirits, is secreted in the cortical substance of the brain and spinal marrow, from whence it passes through the medullary substance. This, like the other system, is founded altogether on hypothesis; but it seems to be an hypothesis derived from much more probable principles, and there are many ingenious arguments to be brought in its support.

(w) This pair, soon after its entrance into the meatus auditorius internus, separates into two branches. One of these is of a very soft and pulpy consistence, is called the portio molliis of the seventh pair, and is spread over the inner part of the ear. The other passes out through the aqueduct of Fallopian in a firm chord, which is distinguished as the portio dura, and is distributed to the external ear, and other parts of the neck and face.

(x) The reader will observe, that the amount of these several divisions is only 29 pair. But there is another pair called the spinal, which arises from the medulla spinalis at its beginning, and, ascending through the great foramen of the os occipitis into the cranium, passes out again close to the eighth pair, with which however it does not unite; and it is afterwards distributed chiefly to the muscles of the neck, back, and scapula. In this course it sends off filaments to different parts, and likewise communicates with several other nerves. EXPLANATION OF PLATE XVIII.

Fig. 1. Represents the inferior part of the brain;—the anterior part of the whole spine, including the medulla spinalis;—with the origin and large portions of all the Nerves.

A A, The anterior lobes of the cerebrum. B B, The lateral lobes of the cerebrum. C C, The two lobes of the cerebellum. D, Tuber annulare. E, The passage from the third ventricle to the infundibulum. F, The medulla oblongata, which sends off the medulla spinalis through the spine. G G, That part of the os occipitis which is placed above (H H), the transverse processes of the first cervical vertebra. II, &c. The seven cervical vertebrae, with their intermediate cartilages. KK, &c. The twelve dorsal vertebrae, with their intermediate cartilages. LL, &c. The five lumbar vertebrae, with their intermediate cartilages. M, The os sacrum. N, The os coccygis.

Nerves.—1, The first pair of nerves, named olfactory, which go to the nose. 2, The second pair, named optic, which goes to form the tunica retina of the eye. 3, The third pair, named motor oculi; it supplies most of the muscles of the eye-ball. 4, The fourth pair, named pathetic,—which is wholly spent upon the musculus trochlearis of the eye. 5, The fifth pair divides into three branches.—The first, named ophthalmicus, goes to the orbit, supplies the lacrymal gland, and sends branches out to the forehead and nose.—The second, named superior maxillary, supplies the teeth of the upper jaw, and some of the muscles of the lips.—The third, named inferior maxillary, is spent upon the muscles and teeth of the lower jaw, tongue, and muscles of the lips. 6, The sixth pair, which, after sending off the beginning of the intercostal or great sympathetic, is spent upon the abductor oculi. 7, The seventh pair, named auditory, divides into two branches.—The largest, named portio mollis, is spent upon the internal ear.—The smallest, portio dura, joins to the fifth pair within the internal ear by a reflected branch from the second of the fifth; and within the tympanum, by a branch from the third of the fifth, named chorda tympani.—Vid. fig. 3, near B. 8, &c. The eighth pair, named par vagum,—which accompanies the intercostal, and is spent upon the tongue, larynx, pharynx, lungs, and abdominal viscera. 9, The ninth pair, which are spent upon the tongue. 10, &c. The intercostal, or great sympathetic, which is seen from the fifth pair to the bottom of the pelvis on each side of the spine, and joining with all the nerves of the spine—in its progress supplying the heart, and, with the par vagum, the contents of the abdomen and pelvis. 11, The accessorius, which is spent upon the sternocleido-mastoideus and trapezius muscles. 12, The first cervical nerves;—13, The second cervical nerves;—both spent upon the muscles that lie on the neck, and teguments of the neck and head. 14, The third cervical nerves, which, after sending off (15, &c.) the phrenic nerves to the diaphragm, supply the muscles and tegments that lie on the side of the neck and top of the shoulder. 16, The brachial plexus, formed by the fourth, fifth, sixth, seventh cervical, and first dorsal nerves,—which supply the muscles and tegments of the superior extremity. 17, The twelve dorsal, or proper intercostal nerves, which are spent upon the intercostal muscles and some of the large muscles which lie upon the thorax. 18, The five lumbar pairs of nerves, which supply the lumbar and abdominal muscles, and some of the tegments and muscles of the inferior extremity. 19, The sacro-facitac, or posterior crural nerve, formed by the two inferior lumbar, and three superior of the os sacrum. This large nerve supplies the greatest part of the muscles and tegments of the inferior extremity. 20, The flamchic plexus, formed by the eighth pair. 21, Branches of the solar or celiac plexus, formed by the eighth pair and intercostals, which supply the stomach and chylopoietic viscera. 22, Branches of the superior and inferior mesenteric plexuses, formed by the eighth pair and intercostals, which supply the chylopoietic viscera, with part of the organs of urine and generation. 23, Nerves which accompany the spermatic cord. 24, The hypogastric plexus, which supplies the organs of urine and generation within the pelvis.

Fig. 2, 3, 4, 5. Shew different views of the inferior part of the brain, cut perpendicularly through the middle,—with the origin and large portions of all the nerves which pass out through the bones of the cranium,—and the three first cervical.

A, The anterior lobe. B, The lateral lobe of the cerebrum. C, One of the lobes of the cerebellum. D, Tuber annulare. E, Corpus pyramidale, in the middle of the medulla oblongata. F, The corpus olivare, in the side of the medulla oblongata. G, The medulla oblongata. H, The medulla spinalis.

Nerves.—1, 2, 3, 4, 5, 6, 7, 8, and 9, Pairs of nerves. 10, Nervus accessorius, which comes from—11, 12 and 13, the three first cervical nerves.

PART VII. OF THE SENSES AND THEIR ORGANS.

CHAP. I.

Of the Senses in General.

a, The word sense, among physiologists, seems to imply, not only the sensation excited in the mind by certain impressions made on the body, but likewise the organ destined to receive and transmit these impressions to the sensorium.

b, The senses are usually described as being only five in number; but a very little attention only seems to be required to perceive, that a greater number may very properly be admitted. Hunger and thirst are sensations which have each their peculiar organ; and that of pain seems to be extended through all the parts endowed with sensibility. But the five senses here to be described, are the exterior senses of touch, taste, smelling, vision, and hearing. Each of these organs being of a peculiar structure, is susceptible only of particular impressions, which will be pointed out as we proceed to describe each of them separately.

CHAP. CHAP. II. Of the Sense of Feeling.

a. The sense of feeling is perhaps seated in all parts of the body, but is commonly said to be confined to the nervous papillae of the cutis or true skin, which, with their appendages and their several uses, have been already described.

b. The exterior properties of bodies, such as their solidity, their humidity, their inequality, their smoothness, dryness, or fluidity, and likewise their degree of heat, seem all to be capable of making different impressions on the papillae, and consequently of exciting different ideas in the sensorium commune. But the organ of touch, like all the other senses, is not equally delicate in every part of the body, or in every subject; being in some much more exquisite than in others.

CHAP. III. Of the Taste.

a. The sense of taste is seated chiefly in the tongue, the situation and figure of which are sufficiently known. The tongue is divided into its basis and apex; is thinner at its edges than it is in its middle part; and has a line extending from its basis to its apex, which divides it as it were into two equal portions, and is called linea linguae mediana. The tongue is composed of muscular fibres, which are disposed in every direction. Some of these fibres pass out from it in different ways, and form three muscles on each side; while others are confined altogether to the tongue, and terminate chiefly on its surface.

b. From its superior surface arise an infinite number of papillae, which may be divided into three classes, the capitate, semi-lenticularis, and pyramidales. The first of these are the largest and most easy of demonstration. They are situated towards the basis of the tongue; and are described as resembling mushrooms, which are connected to the tongue only by a very small neck. The semi-lenticularis differ only from the capitate in having the whole surface of their basis attached to the tongue, of which they occupy the middle portion. The pyramidales are more minute papillae, of a conical shape, very numerous on the apex and borders of the tongue.

c. Towards the basis of the tongue, we meet with a little cavity named by Morgagni fossa magna externa, the use of which has not yet been ascertained.

d. The tongue is covered by a continuation of the cuticle which lines the inside of the mouth. This tunic everywhere exactly embraces the papillae, and is exceedingly soft and pulpy from the perpetual warmth and moisture of the parts. At the under part of the tongue it makes a reduplication called the frenum, which serves to prevent the too great motion of the tongue, and to fix it in its situation. But besides this attachment, the tongue is connected, by means of its muscles and membranous ligaments, to the lower jaw, the os hyoideus, and the styloid processes.

e. The tongue receives its arteries and veins from the internal carotids and jugulars. At the sides of the frenum we observe two considerable veins called the

(1) The manner in which this mucus is secreted, is not determined. Some writers have described this membrane as being glandular; but no glands appear to exist in it.

CHAP. IV. Of Smelling.

a. This, like the sense of taste, seems intended to direct us to a proper choice of aliment; and is chiefly seated in the nose, which is distinguished into its external and internal parts. The situation and figure of the former of these do not seem to require a definition. It is composed of bones and cartilages, covered by muscular fibres and by the common integuments. The bones make up the upper portion, and the cartilages the lower one. The septum narium, like the nose, is likewise in part bony, and in part cartilaginous. These bones and their connections were described in the oto-ology.

b. The internal part of the nose, besides the os spongiosum, has six cavities or sinuses, the maxillary, the frontal, and the sphenoid, which were all described with the bones of the head. They all open into the nostrils; and the nose likewise communicates with the mouth, larynx, and pharynx, behind the velum palati.

c. All these several parts, which are included in the internal division of the nose, viz. the inner surface of the nostrils, the lamellae of the os spongiosum, and the sinuses, are lined by a thick and very vascular membrane, which is the membrana pituitaria Schneideri. This membrane is truly the organ of smelling, but its real structure does not yet seem to be perfectly understood. It appears to be a continuation of the cuticle, which lines the inner surface of the mouth. In some parts of the nose it is smooth and firm, and in others it is loose and spongy. It is constantly moistened by a mucilaginous lymph, of which the finer parts are carried off probably by the air we breathe; and the remainder, by being retained in the sinuses, acquires considerable consistence (v).

d. The arteries and veins, which are distributed to this membrane, are branches from the external carotid and jugulars. The first pair of nerves, the olfactory, are are spread over every part of it, and it likewise receives a branch from the fifth pair.

c. After what has been said of the pituitary membrane, it will not be difficult to conceive how the air we draw in at the nostrils, being impregnated with the effluvia of bodies, excites in us that kind of sensation we call smelling. As these effluvia, from their being exceedingly light and volatile, cannot be capable in a small quantity of making any great impression on the extremities of the olfactory nerves, it was necessary to give considerable extent to the pituitary membrane, that by this means a greater number of odoriferous particles might be admitted at the same time. When we wish to take in much of the effluvia of any thing, we naturally close the mouth, that all the air we inspire, may pass through the nostrils; and at the same time, by means of the muscles of the nose, the nostrils are dilated, and a greater quantity of air is drawn into them.

f. In many quadrupeds, the sense of smelling is much more extensive and delicate than it is in the human subject; and in the human subject, it seems to be more perfect, the sense is vivified by a variety of smells. It is not always in the same state of perfection, being naturally affected by every change in the pituitary membrane, and of the lymph with which that membrane is moistened.

CHAP. V. Of the Ear, and Hearing.

a. The ear is commonly distinguished into external and internal. The former includes all that we are able to discover without dissection, and the meatus auditorius, as far as the tympanum; and the latter, all the other parts of the ear.

b. The external ear is a cartilaginous funnel, covered by the common integuments, and attached, by means of its ligaments and muscles, to the temporal bone. Although capable only of a very obscure motion, it is found to have two muscles. Different parts of it are distinguished by different names. All its cartilaginous part is called ala or wing, to distinguish it from the soft and pendent part below, called the lobe. Its outer circle, or border, is called helix; and the semicircle within this, antihelix. The moveable cartilage placed immediately before the meatus auditorius, which it may be made to close exactly, is named tragus; and an eminence opposite to this at the extremity of the antihelix, is called antitragus. The concha is a considerable cavity formed by the extremities of the helix and antihelix. The meatus auditorius, which at its opening is cartilaginous, is covered by a very thin membrane, which is a continuation of the cuticle from the surface of the ear.

c. In this canal we find a yellow wax, which is supposed to be secreted by very minute glands or follicles at the beginning of the meatus. This secretion, which is at first of an oily consistence, defends the membrane of the tympanum from the injuries of the air, and by its bitterness prevents minute insects from entering into the ear. But, when from neglect or disease it accumulates in too great a quantity, it sometimes occasions deafness. The inner extremity of the meatus is closed by a very thin, transparent membrane, the membrana tympani, which is set in a bony circle like the head of a drum. The upper edge of this membrane not being always close to the bone, affords a passage to the air between the external and internal ear. Under the membrana tympani runs a branch of the fifth pair of nerves, called chorda tympani; and beyond this membrane is the cavity of the tympanum, which is about seven or eight lines wide, and half so many in depth; it is irregular, and everywhere lined by a very fine membrane. There are four openings to be observed in this cavity. It communicates with the mouth by means of the Eustachian tube. This canal, which is in part bony and in part cartilaginous, begins by a very narrow opening at the anterior and almost superior part of the tympanum, increasing in size as it advances towards the palate of the mouth, where it terminates by an oval opening. This tube is everywhere lined by the same membrane that covers the inside of the mouth. The real use of this canal does not seem to have been hitherto satisfactorily ascertained; but found would seem to be conveyed through it to the membrana tympani, deaf persons being often observed to listen attentively with their mouths open. Opposite to this is a minute passage, which leads to the sinuosity of the mastoid process; and the two other openings, which are in the internal process of the os petrosum, are the fenestra ovalis and fenestra rotunda, both which are covered by a very fine membrane.

d. There are three distinct bones in the cavity of the tympanum; and these are the malleus, incus, and stapes. Besides these, there is a fourth, which is the os orbicularis, considered by some anatomists as a process of the stapes, which is necessarily broken off by the violence we are obliged to use in getting at these bones; but, when accurately considered, it seems to be a distinct bone.

e. The malleus is supposed to resemble a hammer, being larger at one extremity, which is its head, than it is at the other, which is its handle. The latter is attached to the membrana tympani, and the head of the bone is articulated with the incus.

The incus, as it is called from its shape, though it seems to have less resemblance to an anvil than to one of the dentes molares with its roots widely separated from each other, is distinguished into its body and its legs. One of its legs is placed at the entry of the canal which leads to the mastoid process; and the others, which is somewhat longer, is articulated with the stapes, or rather with the os orbicularis, which is placed between them.

g. The third bone is very properly named stapes, being perfectly shaped like a stirrup. Its basis is fixed into the fenestra ovalis, and its upper part is articulated with the os orbicularis. What is called the fenestra rotunda, though perhaps improperly, as it is more oval than round, is observed a little above the other, in an eminence formed by the os petrosum, and is closed by a continuation of the membrane that lines the inner surface of the tympanum. The flaps and malleus are each of them furnished with a little muscle (z).

h. The labyrinth, is the only part of the ear which remains to be described. It is situated in the os petrosum,

(z) Anatomists have usually described three muscles of the malleus; the externus, obliquus, and internus. Others speak only of two; but the internus only seems to deserve the name of muscle, the others being truly ligaments. sum, and is separated from the tympanum by a partition which is everywhere bony, except at the two fenestrae. It is composed of three parts; and these are the vestibulum, the semicircular canals, and the cochlea.

i. The vestibulum is an irregular cavity, much smaller than the tympanum, situated nearly in the centre of the os petrosum, between the tympanum, the cochlea, and the semicircular canals. It is open on the side of the tympanum by means of the fenestra ovalis, and communicates with the upper portion of the cochlea by an oblong foramen, which is under the fenestra ovalis, from which it is separated only by a very thin partition.

k. Each of the three semicircular canals forms about half a circle of nearly a line in diameter; and running each in a different direction, they are distinguished into vertical, oblique, and horizontal. These three canals open by both their extremities into the vestibulum; but the vertical and the oblique being united together at one of their extremities, there are only five orifices to be seen in the vestibulum.

l. The cochlea is a canal which takes a spiral course, not unlike the shell of a snail. From its basis to its apex it makes two turns and a half; and is divided into two canals by a very thin lamina or septum, which is in part bony, and in part membranous, in such a manner, that these two canals only communicate with each other at the point. One of them opens into the vestibulum, and the other is covered by the membrane that closes the fenestra rotunda. The bony lamella which separates the two canals, is exceedingly thin, and fills about two thirds of the diameter of the canal. The rest of the septum is composed of a most delicate membrane, which lines the whole inner surface of the cochlea, and seems to form this division in the same manner as the two membranous bags of the pleura, by being applied to each other, form the mediastinum.

m. The arteries of the external ear come from the temporal and occipital, and its veins pass into the jugular. The internal ear receives branches of arteries from the basilar and internal carotid; and its veins empty themselves into the sinuses of the dura mater, and into the internal jugular.

n. The portio mollis of the seventh pair is distributed through the cochlea, the vestibulum, and the semicircular canals; and the portio dura sends off a branch to the tympanum, and other branches to the external ear and parts near it.

o. The sense of hearing, in producing which all the parts we have described assist, is occasioned by a certain modulation of the air collected by the funnel-like shape of the external ear, and conveyed through the meatus auditorius to the membrana tympani. That sound is propagated by means of the air, is very easily proved by ringing a bell under the receiver of an air-pump: the sound it affords being found to diminish gradually as the air becomes exhausted, till at length it ceases to be heard at all. Sound moves through the air with great velocity; but the strength of the sound seems to depend on the state of the air, as it is greater in a cold and dense, than in a warm and rarefied air.

p. That the air vibrating in the membrana tympani communicates its vibration to the different parts of the labyrinth, and thus affects the auditory nerve so as to produce sound, seems to be very probable; and it is imagined, that the malleus, by means of its muscle, serves to increase or diminish the tension of the membrana tympani; but the situation, the minuteness, and the variety of the parts which compose the ear, do not permit much to be advanced with certainty concerning their mode of action.

q. Some of these parts seem to constitute the immediate organ of hearing, and these are all the parts of the vestibulum: but there are others which seem intended for the perfection of this sense, without being absolutely essential to it. It has happened, for instance, that the membrana tympani, and the little bones of the ear, have been destroyed by disease, without depriving the patient of the sense of hearing (a).

r. Before we conclude this article, it will be right to explain certain phenomena which will be found to have a relation to the organ of hearing.

s. Every body has, in consequence of particular sounds, occasionally felt that disagreeable sensation which is usually called setting the teeth on edge; and the cause of this sensation is to be traced to the communication which the portio dura of the auditory nerve has with the branches of the fifth pair, which are distributed to the teeth, being probably occasioned by the violent tremor produced in the membrana tympani by these very acute sounds. Upon the same principle we may explain the strong idea of sound which a person who holds a vibrating string between his teeth.

t. The humming which is sometimes perceived in the ear, without any exterior cause, is perhaps occasioned by an increased pulsation of the arteries in consequence of obstructions in some of the parts of the ear. This pulsation, which in a natural and healthy state is slight and regular, may by disease be increased so as to affect the auditory nerve in a manner sufficient to produce the idea of sound.

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**CHAP. VI.**

**OF VISION**

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**a.** The eyes, which constitute the organ of vision, are situated in two bony cavities, named orbits, where they are surrounded by several parts, which are either intended to protect them from external injury, or to assist in their motion.

b. The globe of the eye is immediately covered by two eye-lids or palpebrae, which are composed of muscular fibres covered by the common integuments, and lined by a very fine and smooth membrane, which is from thence extended over part of the globe of the eye, and is called tunica conjunctiva. Each eye-lid is cartilaginous at its edge; and this border, which is called tarsus, is furnished, as we all know, by a row of hairs named cilia or eye-lashes.

c. The cilia serve to protect the eye from insects and minute bodies floating in the air, and likewise to moderate the action of the rays of light in their passage to the retina. At the roots of these hairs there are fe-

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(a) This observation has led to a supposition, that a perforation of this membrane may, in some cases of deafness, be useful; and Mr Chefelden relates, that some years ago a malefactor was pardoned on condition that he should submit to this operation; but the public clamour raised against it was so great, that it was thought right not to perform it. haceous follicles, first noticed by Melchiorius, which discharge a glutinous liniment. Sometimes the fluid they secrete has too much viscidity, and the eye-lids become glued to each other.

d. The upper border of the orbit is covered by the eye-brows or supercilium, which by means of two muscles are capable of being brought towards each other, or of being carried upwards. They have been considered as serving to protect the eyes, but they are probably intended more for ornament than utility (a).

e. The orbits in which the eyes are placed, are furnished with a good deal of fat, which affords a soft bed on which the eye performs its several motions. The inner angle of each orbit, or that part of it which is near the nose, is called canthus major, or the great angle; and the outer angle, which is on the opposite side of the eye, is the canthus minor, or little angle.

f. The little reddish body which we observe in the great angle of the eye-lids, and is called caruncula lachrymalis, is supposed to be of a glandular structure, and, like the follicles of the eye-lids, to secrete an oily humour. But its structure and use do not seem to have been hitherto accurately determined. The surface of the eye is constantly moistened by a very fine limpid fluid called the tears, which is chiefly, and perhaps wholly, derived from a large gland of the conglomerate kind, situated in a small depression of the os frontis near the outer angle of the eye. Its excretory ducts pierce the tunica conjunctiva, just above the cartilaginous borders of the upper eye-lids. When the tears were supposed to be secreted by the caruncle, this gland was called glandula innominata; but now that its structure and uses are ascertained, it very properly has the name of glandula lacrymalis. The tears poured out by the ducts of this gland are, in a natural and healthy state, incessantly spread over the surface of the eye, to keep it clear and transparent, by means of the eye-lids, and as constantly pass out at the opposite corner of the eye or inner angle, through two minute orifices, the puncta lacrymalia (c); being determined into these little openings by a reduplication of the tunica conjunctiva, shaped like a crescent, the two points of which answer to the puncta. This reduplication is named membrana or valvula semilunaris. Each of these puncta is the beginning of a small excretory tube through which the tears pass into a little pouch or reservoir, the sacculus lacrymalis, which lies in an excavation formed partly by the nasal process of the os maxillare superius, and partly by the os uncus. The lower part of this sac forms a duct, called the ductus ad nares, which is continued through a bony channel, and opens into the nose, through which the tears are occasionally discharged (b).

(a) It is observable, that the eye-brows are peculiar to the human species.

(b) It sometimes happens, that this very pellucid fluid which moistens the eye, being poured out through the excretory ducts of the lacrymal gland faster than it can be carried off through the puncta, trickles down the cheek, and is then fluidly and properly called tears. When this secretion is constantly too copious, it constitutes a disease called epiphora; but we all know, that the application of any irritating particles to the eye, and sometimes the passions of the mind, will occasion a temporary increase of this lymph.

(c) When the ductus ad nares becomes obstructed, in consequence of disease, the tears are no longer able to pass into the nostrils; the sacculus lacrymalis becomes distended; and inflammation, and sometimes ulceration, taking place, constitute the disease called fistula lacrymalis.

(d) The tunicallaginosa seems to be formed in this manner, and not by an expansion of the tendons themselves as it has been generally supposed.

(e) Some writers, who have given the name of cornea to all this outer coat, have named what is here and most commonly called sclerotica, cornea opaca; and its anterior and transparent portion, cornea lucida. The optic nerve enters... m, The choroides, or uvea, has been considered as an expansion of the pia mater coat of the optic nerve. In its fore part we observe a circular hole, called the pupil or sight of the eye, which affords a passage to the rays of light. The choroides is composed of two laminae (a); the outermost of which is continued no farther than the edge of the cornea, to which it is attached all round, being observed to form a little whitish area at the place of this union, which is named ligamentum ciliare (b). The inner lamina extends farther to form what is called the iris (i), which is the part we are able to see through the cornea. It derives its name from the difference of its colours, and is perforated in its middle. This perforation is called pupil or sight of the eye. On the under side of the iris we observe many minute fibres called processus ciliares, which pass in radius or parallel lines from the circumference to the center; and the contraction and dilatation of the pupil are supposed to depend on the action of these ciliary processes (x).

n, The posterior surface of the iris, the processus ciliares, and a part of the tunica choroides, are covered by a black mucus, for the purposes of accurate and distinct vision; but the manner in which it is secreted, has not been determined.

o, Immediately under the tunica choroides we find the third and inner coat, called the retina, which is supposed to be merely an expansion of the pulpy substance of the optic nerve, extending to the borders of the crystalline humour.

p, The greatest part of the globe of the eye, within these several tunics, is filled by a very transparent and gelatinous humour, of considerable consistence, which, from its supposed resemblance to fluid glass, is called the vitreous humour. It is invested by a very fine and delicate membrane, called tunica vitrea, and sometimes arachnoides. It is supposed to be composed of two laminae, one of which dips into its substance, and by dividing the humour into cells adds to its firmness. The fore-part of the vitreous humour is a little hollowed, to receive a very white and transparent substance of a firm texture, and of a lenticular and somewhat convex shape, named the crystalline humour. It is included in a capsule, which seems to be formed by a separation of the two laminae of the tunica vitrea.

q, The fore-part of the eye is filled by a very thin and transparent fluid, named the aqueous humour, which occupies all the space between the crystalline and the prominent cornea. That part of the choroides which is called the iris, and which comes forward to form the pupil, appears to be suspended, as it were, in this humour; and has occasioned this portion of the eye to be distinguished into two parts. One of these, which is the little space between the anterior surface of the crystalline and the iris, is called the posterior chamber; and the other, which is the space between the iris and the cornea, is called the anterior chamber of the eye. Both these spaces are completely filled with the aqueous humour (z).

r, The eye receives its arteries from the internal carotid, and its veins empty themselves chiefly into the external jugulars. Some of the ramifications of these vessels appear on the inner surface of the iris, where they are seen to make very minute convolutions, which are sufficiently remarkable to be distinguished by the name of circulus arteriosus, though perhaps improperly, as they seem to be chiefly branches of veins.

s, The optic nerve passes in at the posterior part of the eye, in a considerable trunk, to be expanded for the purposes of vision, of which it is now universally supposed to be the immediate seat. But Mefris Mariotte and Mery contended, that the choroides is the seat of this sense; and the ancients supposed the crystalline to be so. Besides the optic, the eye receives branches from other nerves, but chiefly from the third pair.

t, The humours of the eye, together with the cornea, are calculated to refract and converge the rays of light in such a manner as to form at the bottom of the eye a distinct image of the object we look at; and the point where these rays meet, is called the focus of the eye. On the retina, as in a camera obscura, the object is painted in an inverted position; and it is only by habit that we are enabled to judge of its true situation, and likewise of its distance and magnitude. To a young gentleman, who was born blind, and who was couched by Mr Chefelden, every object (as he expressed himself) seemed to touch his eyes, as what he felt did his skin; and he thought no objects so agreeable as those which were smooth and regular, although for some time he could form no judgment of their shape, or guess what it was in any of them that was pleasing to him.

u, In order to paint objects distinctly on the retina, the cornea is required to have such a degree of convexity, that the rays of light may be collected at a certain point so as to terminate exactly on the retina. If the cornea is too prominent, the rays, by diverging too soon, will be united before they reach the retina, as is the case with near-sighted people, or myopes; and, on the contrary, if it is not sufficiently convex, the rays

ters into the eye at its posterior part; and as only its pulpy substance is supposed to form the retina, the sclerotica has with great probability been ascribed to the dura mater covering of that nerve.

(a) The inner lamina is exceedingly vascular; and having been first described by Ruysh, is called Ruyshiana.

(b) M. Lieutard seems with more propriety to have named it plexus ciliaris, as it appears to be formed by very numerous and minute filaments of nerves of the third pair.

(i) The iris has been sometimes described as a distinct coat, and called uvea.

(x) Besides these processes, anatomists usually describe the circular fibres of the iris, but they do not seem to be capable of demonstration. The processus ciliares have likewise been differently spoken of, being sometimes described as being composed of muscular fibres, and sometimes as being of a ligamentous texture; but a later and more probable opinion is, that they are neither muscular nor ligamentary, but filaments of nerves derived from the plexus ciliaris.

(z) When the crystalline becomes opaque so as to prevent the passage of the rays of light to the retina, it constitutes what is called a cataract; and the operation of couching consists in removing the diseased crystalline from its bed in the vitreous humour. In this operation, the cornea is perforated, and the aqueous humour escapes out of the eye; but it is constantly renewed again in a very short time. The manner, however, in which it is secreted, has not yet been determined. rays will not be perfectly united when they reach the back part of the eye; and this happens to long-sighted people, or presbyopia, being found constantly to take place as we approach to old age, and the eye gradually flattens (m). These defects are to be supplied by means of glasses. He who has too prominent an eye, will find his vision improved by means of a concave glass; and, upon the same principles, a convex glass will be found useful to a person whose eye is naturally too flat.

EXPLANATION OF PLATE XXI.

Figure 1. Shews the lachrymal canals, after the common teguments and bones have been cut away. a, The lachrymal gland. b, The two puncta lachrymalia, from which the two lachrymal canals proceed to c, the lachrymal sac. d, The large lachrymal duct. e, Its opening into the nose. f, The caruncula lachrymalis. g, The eye-ball.

Fig. 2. An anterior view of the coats and humours of the eye. a a a a, The tunica sclerotica cut in four angles, and turned back. b b b b, The tunica choroides adhering to the inside of the sclerotica, and the ciliary vessels are seen passing over—c c, The retina, which covers the vitreous humour. d d, The ciliary processes, which were continued from the choroid coat. e e, The iris. f, The pupil.

Fig. 3. Shews the optic nerves, and muscles of the eye. a a, The two optic nerves before they meet. b, The two optic nerves conjoined. c, The right optic nerve. d, Musculus attollens palpebrae superioris. e, Attollens oculi. f, Adductor. g g, Obliquus superior, or trochlearis. h, Adductor. i, The eye-ball.

Fig. 4. Shews the eye-ball with its muscles. a, The optic nerve. b, Musculus trochlearis. c, Part of the os frontis, to which the trochlea or pulley is fixed, through which,—d, The tendon of the trochlearis passes. e, Attollens oculi. f, Adductor oculi. g, Adductor oculi. h, Obliquus inferior. i, Part of the superior maxillary bone to which it is fixed. k, The eye-ball.

Fig. 5. Represents the nerves and muscles of the right eye, after part of the bones of the orbit have been cut away. A, The eye-ball. B, The lachrymal gland. C, Musculus adductor oculi. D, Attollens. E, Levator palpebrae superioris. F, Depressor oculi. G, Adductor. H, Obliquus superior, with its pulley. I, Its insertion into the sclerotic coat. K, Part of the obliquus inferior. L, The anterior part of the os frontis cut. M, The cribrum galli of the ethmoid bone. N, The posterior part of the sphenoid bone. O, Transverse spinous process of the sphenoid bone. P, The carotid artery, denuded where it passes thro' the bones. Q, the carotid artery within the cranium. R, The ocular artery.

Nerves.—a a, The optic nerve. b, The third pair.—c, Its joining with a branch of the first branch of the fifth pair, to form l, The lenticular ganglion,—which sends off the ciliary nerves. d, e e, The fourth pair. f, The trunk of the fifth pair. g, The first branch of the fifth pair, named ophthalmic.—h, The frontal branch of it. i, Its ciliary branches, along with which the nasal twig is sent to the nose. k, Its branch to the lachrymal gland. l, The lenticular ganglion. m, The second branch of the fifth pair, named superior maxillary. n, The third branch of the fifth pair, named inferior maxillary. o, The fifth pair of nerves,—which sends off p, The beginning of the great sympathetic. q, The remainder of the fifth pair, spent on c, The abductor oculi.

Fig. 6. Represents the head of a youth, where the upper part of the cranium is sawed off,—to shew the upper part of the brain, covered by the pia mater, the vessels of which are minutely filled with wax. A A, The cut edges of the upper part of the cranium. B B, The two hemispheres of the cerebrum. C C, The incisure made by the falx. D, Part of the tentorium cerebello super expansum. E, Part of the falx, which is fixed to the cribrum galli.

Fig. 7. Represents the parts of the external ear, with the parotid gland and its duct. a a, The helix. b, The antihelix. c, The antitragus. d, The tragus. e, The lobe of the ear. f, The cavitas innominata. g, The scapha. h, The concha. i i, The parotid gland. k, A lymphatic gland, which is often found before the tragus. l, The duct of the parotid gland. m, Its opening into the mouth.

Fig. 8. A view of the posterior part of the external ear, meatus auditorius, tympanum, with its small bones, and Eustachian tube of the right side. a, The back part of the meatus, with the small ceruminous glands. b, The incus. c, Malleus. d, The chorda tympani. e, Membrana tympani. f, The Eustachian tube. g, Its mouth, from the faucies.

Fig. 9. Represents the anterior part of the right external ear, the cavity of the tympanum—it's small bones, cochlea, and semi-circular canals. a, The malleus. b, Incus with its long leg, resting upon the stapes. c, Membrana tympani. d, e, The Eustachian tube, covered by part of—f f, The musculus circumflexus palati. 1, 2, 3, The three semicircular canals. 4, The vestibule. 5, The cochlea. 6, The portio mollis of the seventh pair of nerves.

Fig. 10. Shews the muscles which compose the fleshy substance of the tongue. a a, The tip of the tongue, with some of the papillae minima. b, The root of the tongue. c, Part of the membrane of the tongue, which covered the epiglottis. d d, Part of the musculus hyo-glossus. e, The lingualis. f, Genio-glossus. g g, Part of the stylo-glossus.

(m) Upon this principle they who in their youth are near-sighted may expect to see better as they advance in life, and their eyes gradually become more flat.