among ecclesiastical writers, imports whatever is set apart, separated, or divided; but is most usually meant to express the cutting off a person from the privileges of society, and communion with the faithful.

The anathema differs from excommunication in the circumstances of being attended with curses and execrations. It was practised in the primitive church against notorious offenders; and the form of that pronounced by Synecus against one Andronicus, is as follows: "Let no church of God be open to Andronicus, but let every sanctuary be shut against him. I admonish both private men and magistrates, neither to receive him under their roof, nor to their table; and priests more especially, that they neither converse with him living, nor attend his funeral when dead."

Several councils also have pronounced anathemas against such as they thought corrupted the purity of the faith; and their decisions have been conceived in the following form: *Si quis dixerit*, &c., *anathema sit*.

There are two kinds of anathemas, the one judiciary, and the other abjuratory. The former can only be denounced by a council, a pope, or a bishop; the latter makes a part of the ceremony of abjuration, the convert being obliged to anathematize the hereby he abjures.

**Anathema**, in heathen antiquity, was an offering or present made to some deity, and hung up in the temple. Whenever a person left off his employment, it was usual to dedicate the tools to the patron-deity of the trade. Persons too who had escaped from imminent danger, as shipwreck and the like, or had met with any other remarkable instance of good fortune, seldom failed to testify their gratitude by some present of this kind.

**Anathema** likewise denotes Christian offerings, otherwise called donations. See **Donations**.

**Anathematizing**, the act of pronouncing an anathema against some person. See **Anathema**.

**Anaticula**, little duck, in the ancient Roman customs, a term of fondness used by lovers.

**Anatifer a concha**, the trivial name of a species of the cephalopoda, a tusked animal. See **Lepas**.

**Anatolia**, in geography, the same with Natolia. See **Natolia**.

**Anatomical**, an epithet applied to anything belonging to anatomy. See **Anatomy**.

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**ANATOMY**

**Anatomy** is the art of dissecting the solid parts of animal bodies, with a view to discover their structure, connection, and uses.

Anatomy is not only the basis of all medical knowledge, but is a very interesting object to the philosopher and natural historian.

In treating this useful subject, we shall divide it into the following parts: I. Of the Bones. II. Of the Muscles. III. Of the Arteries. IV. Of the Veins. V. Of the Nerves. VI. Of such parts of the body as are not comprehended in any of the above, e.g. The Brain, Thorax, Abdomen, &c., &c.

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**PART I.**

**OF THE BONES.**

**Sect. I. Of the Bones in general.**

Before we examine the structure of the bones, the periosteum, a membrane with which they are covered, must be described.

The periosteum can be divided into layers of fibres. The exterior ones, composed of the fibres of the muscles connected to the bones, vary in their number, size, and direction, and consequently occasion a very great difference in the thickness and strength of the periosteum of different bones. The internal layer is everywhere nearly of a similar structure, and has its fibres in the same direction with those of the bone to which they are contiguous.

Except where muscles, cartilages, or ligaments, are inserted into the periosteum, its external surface is connected to the surrounding parts by thin cellular membranes, which can easily be stretched considerably, but shorten themselves whenever the stretching force is removed.

When the periosteum is torn off from bones, we see a great number of white threads produced from that membrane into them; and after a successful injection of the arteries with a red liquor, numerous vessels are not only seen on the periosteum, but most of the fibres sent from the membrane to the bone show themselves to be vessels entering it, with the injected liquor in them; and when they are broken, by tearing off the periosteum, the surface of the bone is almost covered with red points.

The great sensibility of the periosteum in the deep-seated species of paronychia, in exostoses, nodi, tophi, and gummatia, from a lues venerea, or whenever this membrane is in an inflamed state, is a sufficient proof that it is well provided with nerves; though they are perhaps too small to be traced.

The chief uses of the periosteum are: 1. To allow the muscles, when they contract or are stretched, to move... and slide easily upon the bones. 2. To keep in due order, and to support the vessels in their passage to the bones. 3. By being firmly braced on the bones, to assist in setting limits to their increase, and to check their overgrowth. 4. To strengthen the conjunction of the bones with their epiphyses, ligaments, and cartilages, which are easily separated in young creatures, when this membrane is taken away. 5. To afford convenient origin and insertion to several muscles which are fixed to this membrane. And, lastly, to warn us when any injury is offered to the parts it covers.

The Bones are the most hard and solid parts of the body, and generally of a white colour; only in a living creature they are bluish, which is owing to the blood in the small vessels under their surface.

Bones are composed of a great many plates, each of which is made up of fibres or strings united by smaller fibrils; which being irregularly disposed and interwoven with the other larger fibres, make a reticular work.—This texture is plainly seen in the bones of fetuses, which have not their parts closely compacted, and in the bones of adults, which have been burnt, long exposed to the weather, or whose composition has been made loose by diseases.

The plates are said to be firmly joined to each other by a great number of clavicles, or small bony processes, which, rising from the inner plates, pierce through some, and are fixed into the more external ones.

Though the exterior part of bones is composed of firm compact plates, yet they are all more or less cavernous internally. In some, the solid sides are brought so near, that little cavity can be seen; and in others, the cavities are so large, that such bones are generally esteemed to be hollow or spongy. But the internal spongy texture is most evident in young animals.

This spongy, cavernous, internal part of bones, is generally called their cancelli or lattice-work.

The twisting and windings which these cancelli make, and the interfaces which they leave, differ considerably in figure, number, and size; and therefore form little cells, which are as different, but communicate with each other.

The cancelli sustain the membranous bags of the marrow which are stretched upon them, and thereby hinder these membranous parts from being torn or removed out of their proper places, in the violent motions and different postures which the bones are employed in.

The depressions between the fibres of the external plates of bones appear like so many furrows on their surface, into each of which the periosteum enters.

Both on the ridges and furrows, numerous little pits or orifices of canals are to be seen, by which the vessels pass to and from the bones.

After a successful injection, the arteries can be traced in their course from the pits to the plates and fibres.

We may conclude, from arteries being accompanied with veins, so far as we can trace them in every other part of the body, that there are also veins in the bones.

The bones of a living animal are so insensible that they can be cut, rapped, or burnt, without putting the creature to pain, and the nerves distributed in their substance cannot be strewed by dissection; from which it might be inferred, that they have no nerves distributed to them: But the general tenor of nature, which betows nerves to all the other parts, should prevent our drawing such a conclusion.

The vascular texture of bones must make them subject to obstructions, ecchymoses, ulcers, gangrenes, and most other diseases which the softer parts are affected with; and therefore there may be a greater variety of caries than is commonly described.

On the internal surface of the solid parts of bones, there are orifices of canals, which pass outwards through the plates to open into other canals that are in a longitudinal direction, from which other transverse passages go out to terminate in other longitudinal canals; and this structure is continued through the whole substance of bones, both these kinds of canals becoming smaller gradually as they approach the outer surface.—These canals are to be seen to the best advantage in a bone burnt till it is white: When it is broken transversely, the orifices of the longitudinal canals are in view; and when we separate the plates, the transverse ones are to be observed.

Most bones have one or more large oblique canals formed through their sides for the passage of the medullary vessels.

The bones sustain and defend the other parts of the body.

Bones are lined within, as well as covered externally, with a membrane; which is therefore commonly called periosteum internum.

The internal periosteum is an extremely fine membrane; nay, frequently it has a loose reticular texture; and therefore it is compared by some to the arachnoid coat of the spinal marrow: so that we cannot expect to divide it into layers as we can divide the external periosteum. We can, however, observe its processes entering into the transverse pores of the bones, where probably they are continued to form the immediate canals for the marrow distributed through the substance of the bones; and along with them vessels are sent, as from the external periosteum, into the bone. These processes being of a very delicate texture, the adhesion of this membrane to the bone is so small, that it separates commonly more easily from the bone than from the marrow which it contains.

From the internal surface of the internal periosteum, a great number of thin membranes are produced; which, passing across the cavity, unite with others of the same kind, and form so many distinct bags, which communicate with each other; and these again are subdivided into communicating vesicular cells, in which the marrow is contained.

The Marrow is the oily part of the blood, separated by small arteries, and deposited in these cells. Its colour and consistence may therefore vary according to the state of the vessels, and their distribution on the membranes of the cells.

Besides the arteries already mentioned as being sent from the bones to the marrow, there is at least one artery for each bone; several bones have more, whose principal use is to convey and fecern this oily matter. The blood, which remains after the secretion of the marrow, is returned by proper veins, which are collected from the membranes into one or two large trunks, to pass out at the same holes at which the arteries enter.

The vessels of the marrow, wrapped up in one common coat from the periosteum, pass through the bones by proper canals; the most considerable of which are about the middle of each bone, and are very oblique.

From the structure of the contents of the bones, we may judge how these parts, as well as others, may be subject to oedema, phlegmon, erysipelas, schirrhus, &c., and may thence be led to a cure of each, before the common consequence, putrefaction, takes place, and frequently occasions the loss of the limb, if not of the patient.

The marrow is of very considerable use to the bones; for by entering their transverse canals, and passing from them into the longitudinal ones, it is communicated to all the plates, to soften and connect their fibres, whereby they are preserved from becoming too brittle.

When the marrow, after having served the uses mentioned, is reassumed into the mass of blood, it corrects the too great acrimony communicated to the saline particles of our fluids by their circulation and heat; in the same manner as lye is blunted by oil in making soap.

Since it is the nature of all oil to become thin and rancid when exposed long to heat, and bones have much oil in their firm hard substance, we may know why an ungrateful smell, and dark-coloured thin ichor, proceed more from corrupted bones than from other parts of the body; and we can understand the reason of the changes of colour which bones undergo, according to their different degrees of mortification.

Though bones so far agree in their structure and annexed parts, yet we may observe a considerable difference among them in their magnitude, figure, situation, substance, connection, uses, &c. Of these we shall only mention two, viz. that some bones are broad and flat, while others are long and round.

The broad bones have thin sides, by the plates being soon and equally sent off to form the lattice-work; which therefore is thicker, and nearly of an equal form all through. By this structure, they are well adapted to their uses, of affording a large enough surface for the muscles to rise from, and move upon, and of defending sufficiently the parts which they inclose.

The round bones have thick strong walls in the middle, and become very thin towards their ends, which is owing to very few plates separating at their middle; where, on that account, the cancelli are so fine and small that they are not taken notice of: But such bones are said to have a large reservoir of oil in this place. Towards their ends the lattice-work becomes very thick, and rather more complete than in the other sort of bones. These round bones having strong forces naturally applied to them, and being otherwise exposed to violent injuries, have need of a cylindrical figure to resist external pressure, and of a considerable quantity of oil to preserve them from becoming too brittle. Besides which, they are advantageously provided with thick sides towards their middle, where the greatest forces are applied to injure them; while their hollowness increases their diameter, and consequently their strength, to resist forces applied to break them transversely.

Many bones have protuberances, or processes, rising out from them. If a process stands out in a roundish ball, it is called capitulum, or head. If the head is flattened, it obtains the appellation of condyle. A rough unequal protuberance is called tuberosity. When a process rises narrow, and then becomes large, the narrow or small part is named cervix, or neck. Long ridges of bones are called spines. Such processes as terminate in a sharp point, have the general name of corona, or coronoid, bestowed on them, though most of them receive particular names from the resemblance they have, or are imagined to have, to other substances, e.g., mastoid, styloid, &c. Such processes as form brims of cavities, are called supercilia.

Processes serve for the advantageous origin and insertion of muscles, and render the articulations firm and stable.

In children these processes are real epiphyses, or distinct bones, which are afterwards united to the other parts; such are the styloid processes of the temporal bones, processes of the vertebrae, trochanters of the thigh, &c.

On the surfaces of a great many of the bones there are cavities, or depressions: If these are deep, with large brims, authors name them cotylæ; if they are superficial, they obtain the designation of glenæ, or glenoidæ. These general classes are again divided into several species:—Of which pits are small roundish channels sunk perpendicularly into the bone;—furrows are long narrow canals, formed in the surface;—niches or notches, small breaches in the bone;—sinusities, broad, but superficial depressions without brims;—sofa, large deep cavities, which are not equally surrounded by high brims;—sinuses, large cavities within the substance of the bones, with small apertures;—foramina, or holes, canals that pierce quite through the substance of the bones.—When this last sort of cavity is extended any long way within a bone, the middle part retains the name of canal, and its ends are called holes.

The cavities allow the heads of bones to play in them; they lodge and defend other parts; they afford safe passage to vessels, muscles, &c.

To far the greater number of bones, whose ends are not joined to other bones by an immovable articulation, there are smaller ones annexed, which afterwards become scarce distinguishable from the substance of the bone itself. These are called epiphyses, or appendices. Some bones have one, others have two, three, or four of these appendices annexed by the means of cartilages, which are of a considerable thickness in children, but by age become thinner.

Several processes (e.g., trochanters of the thigh, spine of the scapula, &c.) have epiphyses; and processes frequently rise out from epiphyses; for example, at the lower end of the femur, ulna, tibia, &c.

The epiphyses are united chiefly to such bones as are destined for frequent and violent motion; and for this purpose they are wisely framed of a larger diameter than the the bone they belong to; for by this means, the surface of contact between the two bones of any articulation being increased, their conjunction becomes firmer, and the muscles inserted into them act with greater force, by reason of their axes being further removed from the center of motion.

The softness of the ends of bones may be of some advantage in the womb, and at birth, after which the ossification begins at different points to form epiphyses, before the ossification can extend from the middle to the ends of the bones.

However solid and compact adult bones are, yet they were once cartilages, membranes, nay, a mere jelly. This needs no further proof, than repeated observations of embryos when dissected: And how much more tender must the bones be before that time, when neither knife nor eye is capable to discover the least rudiments of them? By degrees they become more solid, then assume the nature of gristles, and at last ossify; the cohesion of their plates and fibres always increasing in proportion to their increased solidity; as is evident from the time necessary to unravel the texture of bones of people of different ages, or of dense and of spongy bones, or of the different parts of the same bone, and from the more tedious exfoliations of the bones of adults than of children.

The ossification of bones depends principally on their vessels being so disposed, and of such diameters, as to separate a liquor, which may easily turn into a bony substance, when it is deprived of its thinner parts; as seems plain from the observation of the callous matter separated after fractures and ulcers, where part of the bone is taken out: For in these cases, the vessels extending themselves, and the liquors added to them, are gradually formed into granulated flesh; which fills up all the space where the bone is taken from, then hardens, till it becomes as firm as any other part of the bone. This happens frequently, even when the ends of the diseased bone are at a considerable distance from each other.

The induration of bones is also greatly assisted by their being exposed, more than any other parts, to the strong pressure of the great weights they support, to the violent contraction of the muscles fixed to them, and to the force of the parts they contain, which endeavour to make way for their own further growth. By all this pressing force, the solid fibres and vessels of bones are thrust closer; and such particles of the fluids conveyed in these vessels as are fit to be united to the fibres, are sooner and more firmly incorporated with them, while the remaining fluids are forcibly driven out by the veins, to be mixed with the mass of blood. In consequence of this, the vessels gradually diminish as the bones harden. From which again we can understand one reason, why the bones of young animals sooner re-unite after a fracture than those of old; and why cattle that are put too soon to hard labour, seldom are of such large size as others of the same breed, who are longer kept from labour.

From the effects of pressure only it is, that we can account for the bones of old people having their sides much thinner, yet more dense and solid, while the cavities are much larger than those of young people; and for the prints of muscles, vessels, &c., being so much more strongly marked on the surfaces of the former than of the latter, if they belong to people of near the same condition in life.—Pressure must likewise be the cause, which, in people of equal ages, makes these prints stronger in the bones of those who had much labour and exercise, than they are in people who have led an indolent inactive life.

Having thus considered the bones when single, we shall next shew the different manner of their conjunctions. To express these, anatomists have contrived a great number of technical terms; about the meaning, propriety, and clasping of which, there has been a variety of opinions. Some of these terms it is necessary to retain, since they serve to express the various circumstances of the articulations, and to understand the writers on this subject.

The Articulations are most commonly divided into three classes, viz. symphyses, synarthroses, and diarthroses.

Symphyses, which properly signifies the concretion or growing together of parts, when used to express the articulations of bones, does not seem to comprehend, under the meaning generally given to it, anything relating to the form or motion of the conjoined bones; but by most authors only denote the bones to be connected by some other substance; and as there are different substances which serve this purpose, therefore they divide it into the three following species:

1. Synchondroses, when a cartilage is the connecting substance: Thus the ribs are joined to the sternum; thus the bodies of the vertebrae are connected to each other; as are likewise the osa pubis.

2. Synchondroses, or syndesmoses, when ligaments are the connecting bodies, as they are in all the moveable articulations.

3. Sutures, when muscles are stretched from one bone to another, as they must be where there are moveable joints.

The second class of articulations, the synarthroses, which is said to be the general term by which the immovable conjunction of bones is expressed, is divided into three kinds.

1. The sutures is that articulation where two bones are mutually indented into each other, or as if they were sewed together. Thus the bones of the head are joined; thus epiphyses are joined to the bones, before their full connection and union with them.

2. Gomphoses is the fixing one bone into another, as a nail is fixed in a board: Thus the teeth are secured in their sockets.

3. Schindylesis, or ploughing, when a thin lamella of one bone is received into a long narrow furrow of another: Thus the processus zygos of the sphenoid, and the nasal process of the ethmoid bone, are received by the vomer.

The third class, or diarthroses, is the articulation where the bones are so loosely connected as to allow large motion. This is subdivided into three kinds. The first is *enarthrosis*, or the ball and socket, when a large head is received into a deep cavity; as the head of the os femoris is into the acetabulum coxæ.

The second is *arthrodia*, when a round head is received into a superficial cavity; as in the articulation of the arm-bone and scapula. These two species of diarthrosis allow motion to all sides.

The third is *ginglimus*, which properly signifies the hinge of a door or window; in it the parts of the bones mutually receive and are received, and allow of motion two ways: Workmen call it *charnal*.

The ginglimus is generally divided into three kinds, to which some give the names of contiguous, distant, and compound.

The first kind of ginglimus is, when a bone has several protuberances and cavities, which answer to as many cavities and processes of the other bone, with which it is articulated; as in the conjunction of the femur with the tibia.

The second species is, when a bone receives another at one end, and is received by the same bone at the other end; as in the radius and ulna.

The last sort is, when a bone receives another, and is received by a third; as in the oblique processes of the vertebrae.

If the moveable bones are not connected and kept firm by some strong substance, they would be luxated at every motion of the joints: and if their hard, rough, unequal surfaces were to play on each other, their motion would not only be difficult, but the loss of substance from attrition would be great. Therefore ligaments are made to obviate the first, and cartilages to prevent the other inconvenience. But because ligaments and cartilages turn rigid, inflexible, and rough, unless they are kept moist, a sufficient quantity of proper liquor is supplied for their lubrication, and to preserve them in a flexible state. Seeing then these parts are so necessary to the articulations, we shall next consider their structure, situation, and uses, so far as they are subservient to the bones, and their motions.

**Ligaments** are white flexible bodies, thicker and firmer than membranes, and not so hard or firm as cartilages, without any remarkable cavity in their substance, difficulty stretched, and with little elasticity; serving to connect one part to another, or to prevent the parts to which they are fixed from being removed out of that situation which is useful and safe.

After maceration in water, the ligaments can easily be divided; and each ligamentous layer appears composed of fibres, the largest of which are disposed in a longitudinal direction.

The arteries of ligaments are very conspicuous after a tolerable injection, and the larger trunks of their veins are sometimes to be seen full of blood.

Such ligaments as form the sides of cavities, have numerous orifices of their arteries opening upon their internal surface, which keep it always moist; if we rub off that moisture, and then press the ligament, we can see the liquor ouzing out from small pores; and we can force thin liquors, injected by the arteries, into the cavities formed by ligaments.

These exhalent arteries must have corresponding absorbent veins, otherwise the cavities would soon be too full of liquor.

Ligaments then must be subject to the diseases common to other parts, where there is a circulation of fluids, allowance always being made for the size of vessels, nature of the fluids, and firmness of the texture of each part.

Some authors have alleged, that ligaments are insensible, and consequently that they have no nerves. But the violent racking pain felt on the least motion of a joint labouring under a rheumatism, the seat of which disease seems often to be in the ligaments, and the sufferable torture occasioned by incisions of ligaments, and by a collection of acid matter in a joint, or by tophi in the gout, would persuade us, that they are abundantly supplied with nerves.

The ligaments which connect the moveable bones commonly rise from the conjunction of the epiphyses of the one bone, and are inserted into the same place of the other; or where epiphyses are not, they come out from the cervix, and beyond the supercilia of the articulated bones; and after such a manner, in both cases, as to include the articulation in a purse or bag; with this difference, depending on their different motions, that where the motion is only to be in two directions, the ligaments are strongest on those sides towards which the bones are not moved; and when a great variety of motions is designed to be allowed, the ligaments are weaker than in the former sort of articulations, and are nearly of the same strength all round.

Part of the capsular ligaments is composed of the periosteum, continued from one bone to another, and their internal layer is continued on the parts of the bone or cartilage which the ligament includes.

Besides these common capsular ligaments of the joints, there are particular ones in several places, either for the firmer connection of the articulated bones, or for restraining and confining the motion to some one side; such are the crofs and lateral ligaments of the knee, the round one of the thigh, &c.

From this account of the ligaments, we may conclude, that, *ceteris paribus*, in whatever articulation the ligaments are few, long, and weak, the motion is more free and quick; but luxations happen frequently: And, on the contrary, where the ligaments are numerous, short, and strong, the motion is more confined; but such a joint is less exposed to luxations.—Whence we may judge how necessary it is to attend to the different ligaments, and the changes which have been made on them by a luxation, when it is to be reduced.

Ligaments also supply the place of bones in several cases to advantage: Thus the parts in the pelvis are more safely supported below by ligaments, than they could have been by bone.—The ligaments placed in the great holes of the osa innominata, and between the bones of the fore-arm and leg, afford convenient origin to muscles.—Immoveable bones are firmly connected by them; of which the conjunction of the os sacrum and innominatum is an example.—They afford a socket for moveable bones to play in, as we see part of the astragalus does on the ligament stretched from the heel-bone to the scaphoid.

Numerous inconveniences may arise from too long or short, strong or weak, lax or rigid ligaments.

Cartilages are solid, smooth, white elastic substances, between the hardness of bones and ligaments, and covered with a membrane, named perichondrium, which is of the same structure and use to them as the periosteum is to the bones.

Cartilages are composed of plates, which are formed of fibres, disposed much in the same way as those of bones are; as might be reasonably concluded from observing bones in a cartilaginous state before they ossify, and from seeing, on the other hand, so many cartilages become bony. This may be still further confirmed, by the exfoliation which cartilages are subject to, as well as bones.

The perichondrium of several cartilages, for example, those of the ribs and larynx, has arteries which can be equally well injected with those of the periosteum.

The granulated flesh which rises from the ends of metacarpal or metatarsal bones, when the cartilage exfoliates, after a finger or toe has been taken off at the first joint, is very sensible, from which the existence of nerves in cartilages may be inferred.

While cartilages are in a natural state, it is to be remarked, first, That they have no cavity in their middle for marrow. Secondly, That their outer surface is soft, which renders them more flexible. Thirdly, That they do not appear to change their texture near so much by acids as bones do. And, lastly, That as the specific gravity of cartilages is near a third less than that of bones, so the cohesion of their several plates is not so strong as in bones; whence cartilages laid bare in wounds or ulcers, are not only more liable to corrupt, but exfoliate much sooner than bones do.

Cartilages seem to be principally kept from ossifying, either by being subjected to alternate motions of flexion and extension, the effects of which are very different from any kind of simple pressure, or by being constantly moistened: Thus, the cartilages on the articulated ends of the great bones of the limbs, and the moveable ones placed between the moving bones in some articulations, which are obliged to suffer many and different flexions, and are plentifully moistened, scarce ever change into bone; while those of the ribs and larynx are often ossified.

The cartilages subservient to bones, are sometimes found on the ends of bones which are joined to no other; but are never wanting on the ends, and in the cavities of such bones as are designed for motion.

The uses of cartilages, so far as they regard bones, are, to allow, by their smoothness, such bones as are designed for motion, to slide easily without detrition, while, by their flexibility, they accommodate themselves to the several figures necessary in different motions, and, by their elasticity, they recover their natural position and shape as soon as the pressure is removed.

This springy force may also assist the motion of the joint to be more expeditious, and may render shocks in running, jumping, &c., less.—To these cartilages we chiefly owe the security of the moveable articulations: For without them the bony fibres would sprout out, and intimately coalesce with the adjoining bone; whence a true anchylosis must necessarily follow; which never fails to happen when the cartilages are eroded by acid matter, or ossified from want of motion or defect of liquor, as we see often happens after wounds of the joints, painedarthrocece, scrophula, and spina ventosa, or from old age, and long immobility of joints. The moveable cartilages interposed in joints, serve to make the motions both freer and more safe than they would otherwise be.

Those placed on the ends of bones that are not articulated, as on the spine of the os ilium, base of the scapula, &c., serve to prevent the bony fibres from growing out too far.—Cartilages sometimes serve as ligaments, either to fasten together bones that are immovably joined, such are the cartilages between the os sacrum and osa ilium, the os pubis, &c., or to connect bones that enjoy manifest motion, as those do which are placed between the bodies of the true vertebrae, &c.—Cartilages very often do the office of bones to greater advantage, than these last could, as in the cartilages of the ribs, those which supply brims to cavities, &c.

Too great thicknesses or thinnesses, length or shortnesses, hardness or suppleness of cartilages, may therefore cause great disorders in the body.

The liquor, which principally serves to moisten the ligaments and cartilages of the articulations, is supplied by glands, which are commonly situated in the joint, after such a manner as to be gently pressed, but not destroyed by its motion. By this means, when there is the greatest necessity for this liquor, that is, when the most frequent motions are performed, the greatest quantity of it must be separated. These glands are soft and pappy, but not friable: In some of the large joints they are of the conglomerate-kind, or a great number of small glandules are wrapped up in one common membrane. Their excretory ducts are long, and hang loose, like so many fringes, within the articulation; which, by its motion and pressure, prevents obstructions in the body of the gland or its excresories, and promotes the return of this liquor, when fit to be taken up by the absorbent vessels, which must be in the joints, as well as in the other cavities of the body; and, at the same time, the pressure on the excretory ducts hinders a superfluous unnecessary secretion, while the fimbriated disposition of these excresories does not allow any of the secreted liquor to be pushed back again by these canals towards the glands.

Very often these fountains of slimy liquor appear only as a net-work of vessels.—Frequently they are almost concealed by cellular membranes containing the fat;—and sometimes small simple mucous folliculi may be seen.

The different joints have these organs in different numbers and sizes; the conglomerate ones don't vary much, especially as to situation, in the similar joints of different bodies; but the others are more uncertain.

Upon pressing any of these glands with the finger, one can can squeeze out of their excretories a mucilaginous liquor, which somewhat resembles the white of an egg, or serum of the blood; but it is manifestly felt to the taste. It does not coagulate by acids or by heat, as the serum does, but by the latter turns first thinner, and, when evaporated, leaves only a thin salt film.

The vessels which supply liquors for making the secretion of this mucilage, and the veins which bring back the blood remaining after the secretion, are to be seen, without any preparation; and, after a tolerable injection of the arteries, the glands are covered with them.

In a sound state, we are not conscious of any sensibility in those glands; but, in some cases, when they inflame and suppurate, the most racking pain is felt in them: a melancholy, though a sure proof that they have nerves.

These mucilaginous glands are commonly lodged in a cellular substance; which is also to be observed in other parts of the bag formed by the ligaments of the articulation; and contains a fatty matter, that must necessarily be attenuated, and forced through the including membranes into the cavity of the joint, by the pressure which it suffers from the moving bones.

After the liquor of the articulations becomes too thin and unserviceable, by being constantly pounded and rubbed between the moving bones, it is reassumed into the mass of blood by the absorbent vessels.

**Sect. II. Of the Skeleton.**

Among anatomists, Skeleton is universally understood to signify the bones of animals connected together, after the teguments, muscles, bowels, glands, nerves, and vessels are taken away.

A skeleton is said to be a natural one, when the bones are kept together by their own ligaments; and it is called artificial, when the bones are joined with wire, or any other substance which is not part of the creature to which they belonged.

The human skeleton is generally divided into the Head, the Trunk, the Superior and the Inferior Extremities.

**Of the Head.**

By the Head is meant all that spheroidal part which is placed above the first bone of the neck. It therefore comprehends the cranium and bones of the face.

The cranium, helmet, or brain-case, consists of several pieces, which form a vaulted cavity, for lodging and defending the brain and cerebellum, with their membranes, vessels, and nerves.

The cavity of the cranium is proportioned to its contents. Hence such a variety of its size is observed in different subjects; and hence it is neither so broad nor so deep at its fore-part, in which the anterior lobes of the brain are lodged, as it is behind, where the large posterior lobes of the brain, and the whole cerebellum, are contained.

The external surface of the upper part of the cranium is very smooth, and equal, being only covered with the periosteum, (common to all the bones; but in the skull, distinguished by the name of pericranium), the thin frontal and occipital muscles, their tendinous aponeurosis, and with the common teguments of the body; while the external surface of its lower part has numerous risings, depressions, and holes, which afford convenient origin and insertion to the muscles that are connected to it, and allow safe passage for the vessels and nerves that run through and near it.

The internal surface of the upper part of the skull is commonly smooth, except where the vessels of the dura mater have made furrows in it, while the bones were soft.—Surgeons should be cautious when they trepan here, lest, in sawing or raising the bone where such furrows are, they wound these vessels.—In the upper part of the internal surface of several skulls, there are likewise pits of different magnitudes and figures, which seem to be formed by some parts of the brain being more luxuriant and prominent than others. Where these pits are, the skull is so much thinner than anywhere else, that it is often rendered diaphanous, the two tables being closely compacted without a diploe; the want of which is supplied by vessels going from the dura mater into a great many small holes observable in the pits.—The knowledge of these pits should teach surgeons to saw cautiously and slowly through the external table of the skull, when they are performing the operation of the trepan; since, in a patient whose cranium has these pits, the dura mater and brain may be injured, before the instrument has pierced near the ordinary thickness of a table of the skull.—The internal bafe of the skull is extremely unequal for lodging the several parts and appendices of the brain and cerebellum, and allowing passage and defense to the vessels and nerves that go into, or come out from these parts.

The bones of the cranium are composed of two tables, and intermediate cancelli, commonly called their diploe. The external table is thickest; the inner, from its thinness and consequent brittleness, has got the name of vitrea.

The diploe has much the same texture and uses in the skull, as the cancelli have in other bones.

The diploe of several old subjects is so obliterated, that scarce any vestige of it can be seen; neither is it observable in some of the hard craggy bones at the base of the skull. Hence an useful caution to surgeons who trust to the bleeding, want of resistance, and change of sound, as certain marks, in the operation of the trepan, for knowing when their instrument has sawed through the first table, and reached the diploe.

The cranium consists of eight bones, five of which are said to be proper, and the other two are reckoned common to it and to the face.—The five proper are, the os frontis, two ossa parietalia, two ossa temporum, and the os occipitis.—The common are, the os ethmoides, and sphenoides.

The os frontis forms the whole fore-part of the vault; the two ossa parietalia form the upper and middle part of it; the ossa temporum compose the lower part of the sides; sides; the os occipitis makes the whole hinder-part, and some of the base; the os ethmoides is placed in the fore-part of the base; and the os sphenoides is in the middle of it.

These bones are joined to each other by five sutures; the names of which are, the coronal, lambdoid, sagittal, and two squamosus.

The coronal suture is extended over the head, from within an inch or so of the external canthus of one eye, to the like distance from the other; which being near the place where the ancients wore their vittae, coronae, or garlands, this suture has hence got its name.—Though the indentations of this suture are conspicuous in its upper part, yet an inch or more of its end on each side has none of them; for it is squamosus and smooth there.

The lambdoidal suture begins some way below, and farther back than the vertex or crown of the head, whence its two legs are stretched obliquely downwards, and to each side, in the form of the Greek letter Λ, and are generally said to extend themselves to the base of the skull.

This suture is sometimes very irregular, being made up of a great many small sutures, which surround so many little bones that are generally larger and more conspicuous on the external surface of the skull than internally. These bones are generally called trigonum, or Wormiana.

The sagittal suture is placed longitudinally, in the middle of the upper part of the skull, and commonly terminates at the middle of the coronal, and of the lambdoid sutures; between which it is said to be placed, as an arrow is between the string and bow.—However, this suture is frequently continued through the middle of the os frontis, down to the root of the nose; which often happens in women than men.

The squamosus agglutinations, or false sutures, are one on each side, a little above the ear, of a semicircular figure, formed by the overlapping (like one scale upon another) of the upper part of the temporal bones, on the lower part of the parietal, where, in both bones, there are a great many small risings and furrows, which are indented into each other; though these inequalities do not appear till the bones are separated.

The bones of the skull are joined to those of the face by schyzodesis and sutures.—The schyzodesis is in the partition of the nose.—The sutures said to be common to the cranium and face are five, viz., the ethmoidal, sphenoidal, transverse, and two zygomatic.—Parts however of these sutures are at the junction of only the bones of the skull.

The ethmoidal and sphenoidal sutures surround the bones of these names; and in some places help to make up other sutures, particularly the squamosus and transverse; and, in other parts, there is but one suture common to these two bones.

The transverse suture is extended quite across the face, from the external canthus of one orbit, to the same place of the other.

The zygomatic sutures are one on each side, being short, and slanting from above obliquely, downwards and backwards, to join a process of the cheek-bone to one of the temporal bones, which advances towards the face; so that the two processes thus united, form a sort of bridge or jugum, under which the temporal muscle passes; on which account the processes, and futures joining them, have been called zygomatic.

The advantages of the sutures of the cranium are these: 1. That this capsule is more easily formed and extended into a spherical figure, than if it had been one continued bone. 2. That the bones which are at some distance from each other at birth might then yield, and allow to the head a change of shape, accommodated to the passage it is engaged in. Whence, in hard labour of child-bed, the bones of the cranium, instead of being only brought into contact, are sometimes made to mount one upon the other. 3. That the dura mater may be more firmly suspended by its processes, which infuse themselves into this conjunction of the bones; for doing this equally, and where the greatest necessity of adhesion is, the sutures are disposed at nearly equal distances, and the large reservoirs of blood, the sinuses, are under or near them. 4. That fractures might be prevented from reaching so far as they would in a continued bony substance. 5. That the connection at the sutures being capable of yielding, the bones might be allowed to separate; which has given great relief to patients from the violent symptoms which they had before this separation happened.

Having gone through the general structure of the cranium, we now proceed to examine each bone of which that brain-case consists.

The Os Frontis has its name from its being the only bone of that part of the face we call the forehead, though it reaches a good deal further. It has some resemblance in shape to the shell of the concha-bivalvis, commonly called the cockle; for the greatest part of it is convex externally, and concave internally, with a serrated circular edge; while the smaller part has processes and depressions, which make it of an irregular figure.

The external surface of the os frontis is smooth at its upper convex part; but several processes and cavities are observable below: for, at each angle of each orbit, the bone juts out to form four processes, two internal, and as many external; which, from this situation, may well enough be named angular. Between the internal and external angular processes of each side, an arched ridge is extended, on which the eye-brows are placed.—Very little above the internal end of each of these superciliary ridges, a protuberance may be remarked, in most skulls, where there are large cavities, called sinuses, within the bone.—Betwixt the internal angular processes, a small process rises, which forms some share of the nose, and thence is named nasal.—Some observe a protuberant part on the edge of the bone, behind each external angular process, which they call temporal processes; but these are inconceivable.—From the under part of the superciliary ridges, the frontal bone runs a great way backwards; which parts may justly enough be called orbital processes. These, contrary to the rest of this bone, are concave externally, for receiving the globes of the eyes, with their muscles, fat, &c.

In each of the orbital processes, behind the middle of the superciliary ridges, a considerable finuosity is observed, where the glandula innominata Galeni, or lachrymalis, is lodged.—Behind each internal angular process, a small pit may be remarked, where the cartilaginous pulley of the musculus obliquus major of the eye is fixed.—Betwixt the two orbital processes, there is a large discontinuation of the bone, into which the cribriform part of the os ethmoides is incased.—The frontal bone frequently has little caverns formed in it here where it is joined to the ethmoid bone.—Behind each external angular process, the surface of the frontal bone is considerably depressed where part of the temporal muscle is placed.

The foramina, or holes, observable on the external surface of the frontal bone, are three in each side.—One in each superciliary ridge, a little removed from its middle towards the nose; through which a twig of the ophthalmic branch of the fifth pair of nerves passes out of the orbit, with a small artery, from the internal carotid, to be distributed to the teguments and muscles of the forehead.—These vessels in some skulls make furrows in the os frontis, especially in the bones of children; and therefore we ought to beware of transverse incisions on either side of the os frontis, which might either open these vessels or hurt the nerves, while they are yet in part within the bone; for, when vessels are thus wounded, it is difficult to stop the hemorrhage, because the adhesion of a part of the artery to the bone hinders its contraction, and consequently styptic can have little effect; the sides of the furrow keep off compressing substances from the artery; and we would with to shun cauteries or echarotics, because they make the bone carious; and nerves, when thus hurt, sometimes produce violent symptoms.—But we must remark, that often, instead of a hole, a notch only is to be seen: Nay, in some skulls, scarce a vestige even of this is left; in others, both hole and notch are observable, when the nerve and artery run separately. Frequently a hole is found on one side, and a notch on the other; at other times we see two holes; or there is a common hole without, and two distinct entries internally. Near the middle of the inside of each orbit, hard by, or in the transverse future, there is a small hole for the passage of the nasal twig of the first branch of the fifth pair of nerves, and of a branch of the ophthalmic artery. This hole is sometimes entirely formed in the os frontis; in other skulls, the sides of it are composed of this last bone, and of the os planum. It is commonly known by the name of orbitarium internum, though anterius should be added, because of the next, which is commonly omitted.—This, which may be called orbitarium internum posterius, is such another as the former; only smaller, and about an inch deeper in the orbit: through it a small branch of the ocular artery passes to the nose.—Besides these six, there are a great number of small holes observable on the outer surface of this bone, particularly in the two protuberances above the eye-brows. Most of these penetrate no further than the sinuses, or than the diploe, if the sinuses are wanting. The place, size, and number of them, are however uncertain: They generally serve for the transmission of small arteries or nerves.

The internal surface of the os frontis is concave, except at the orbital processes, which are convex, to support the anterior lobes of the brain. This surface is not so smooth as the external; for the larger branches of the arteries of the dura mater make some furrows in its sides and back-parts. The finosities from the luxuriant risings of the brain, mentioned when describing the general structure of the cranium, are often very observable on its upper part; and its lower and fore parts are marked with the contortions of the anterior lobes of the brain.—Through the middle of this internal surface, where always in children, and sometimes in old people, the bone is divided, either a ridge stands out, to which the upper edge of the falx is fastened, or a furrow runs, in which the upper side of the superior longitudinal sinus is lodged; on both these accounts chirurgical authors justly discharge the application of the trepan here.

Immediately at the root of this ridge or furrow there is a small hole, which sometimes pierces through the first table, and, in other skulls, opens into the superior sinus of the ethmoid bone within the nose. In it a little process of the falx is lodged, and a small artery, and sometimes a vein, runs; and the superior longitudinal sinus begins here.—This hole, however, is often not entirely proper to the os frontis; for in several skulls, the lower part of it is formed in the upper part of the base of the cribrum galli, which is a process of the ethmoid bone.

The os frontis is composed of two tables, and an intermediate diploe, as the other bones of the cranium are, and in a middle degree of thickness between the os occipitinis and the parietal bones.

The diploe is also exhausted in that part above the eye-brows, where the two tables of the bone separate, by the external being protruded outwards, to form two large cavities, called sinus frontales.—These are divided by a middle perpendicular bony partition.—In some skulls, besides the large perpendicular septum, there are several bony pillars, or short partitions, found in each sinus; in others these are wanting.—For the most part, the septum is entire; at other times it is discontinued, and the two sinuses communicate.—Each sinus commonly opens by a roundish small hole, at the inner and lower part of the internal angular processes, into a sinus formed in the nose, at the upper and back part of the os unguis; near to which there are also some other small sinuses of this bone, the greater part of which open separately nearer the septum narium, and often they terminate in the same common canal with the large ones.

In a natural and sound state, these cavities are of considerable advantage; for the organ of smelling being thus enlarged, the effluvia of odorous bodies more difficulty escape it; and their impressions being more numerous, are therefore stronger, and affect the organ more.—These and the other cavities which open into the nose, increase the sound of our voice, and render it more melodious, by serving as so many vaults to resound the notes. Hence people labouring under a coryza, or stoppage of the nose from any other cause, when they are by the vulgar, though falsely, said to speak through their nose, have such a disagreeable harsh voice.—The liquor separated in the membrane of these sinuses, drips down upon the membrane of the nose to keep it moist.

From the description of these sinuses, it is evident how how useless, nay, how pernicious it must be, to apply a trepan on this part of the skull; for this instrument, instead of piercing into the cavity of the cranium, would reach no further than the sinuses.

The upper circular part of the os frontis is joined to the os parietalia, from one temple to the other, by the coronal suture. From the termination of the coronal suture to the external angular processes, this bone is connected to the sphenoid by the sphenoidal suture. At the external canthi of the eyes, its angular processes are joined by the transverse suture to the os malarum, to which it adheres one third down the outside of the orbits; whence to the bottom of these cavities, and a little up on their internal sides, these orbital processes are connected to the sphenoidal bone by that same suture.—On the inside of each orbit, the orbital process is indented between the cribriform part of the ethmoid bone, and the os planum and unguis.—The transverse suture afterwards joins the frontal bone to the superior nasal processes of the os maxillaria superiors, and to the nasal bones. And, lastly, its nasal process is connected to the nasal lamella of the ethmoid bone.

The frontal bone serves to defend and support the anterior lobes of the brain. It forms a considerable part of the cavities that contain the globes of the eyes, helps to make up the septum narium, organ of smelling, &c. From the description of the several parts, the other uses of this bone are evident.

In a ripe child, the frontal bone is divided through the middle; the superciliary holes are not formed; often a small round piece of each orbital process, behind the superciliary ridge, is not ossified, and there is no sinus to be seen within its substance.

Each of the two Osseae Parietaliae, or bones serving as walls to the encephalon, is an irregular square; its upper and fore sides being longer than the one behind or below. The inferior side is a concave arch; the middle part receiving the upper round part of the temporal bone.—The angle formed by this upper side and the fore one, is so extended, as to have the appearance of a process.

The external surface of each os parietale is convex. Upon it, somewhat below the middle height of the bone, there is a transverse arched ridge, of a whiter colour generally than any other part of the bone; from which, in bones that have strong prints of muscles, we see a great many converging furrows, like so many radii drawn from a circumference towards a centre. From this ridge of each bone the temporal muscle rises; and, by the pressure of its fibres, occasions the furrows just now mentioned.—Below these, we observe, near the semicircular edges, a great many risings and depressions, which are joined to like inequalities on the inside of the temporal bone, to form the squamous suture. The temporal bone may therefore serve here as a buttress, to prevent the lower side of the parietal from starting outwards when its upper part is pressed or struck.

Near the upper fidae of these bones, towards the hind part, is a small hole in each, through which a vein passes from the teguments of the head to the longitudinal sinus.—In several skulls, one of the osseae parietaliae has not this hole; in others, there are two in one bone; and in some not one in either. Most frequently this hole is through both tables; at other times the external table is only perforated.—The knowledge of the course of these vessels may be of use to surgeons, when they make any incision near this part of the head, lest, if the vessels are rashly cut near the hole, they shrink within the substance of the bone, and so cause an obstinate hemorrhage, which neither ligatures nor medicines can stop.

On the inner concave surface of the parietal bones, we see a great many deep furrows, disposed somewhat like the branches of trees: The furrows are largest and deepest at the lower edge of each os parietale, especially near its anterior angle, where sometimes a full canal is formed. They afterwards divide into small furrows, in their progress upwards.—In some skulls a large furrow begins at the hole near the upper edge, and divides into branches, which join with those which come upwards, shewing the communications of the upper and lower vessels of the dura mater.—In these furrows we frequently see passages into the diploe. On the inside of the upper edge of the osseae parietaliae, there is a large sinuosity, frequently larger in the bone of one side than of the other, where the upper part of the falx is fattened, and the superior longitudinal sinus is lodged.—Generally part of the lateral sinuses makes a depression near the angle, formed by the lower and posterior sides of these bones; and the pits made by the prominent parts of the brain are to be seen in no part of the skull more frequent, or more considerable, than in the internal surface of the parietal bones.

The osseae parietaliae are amongst the thinnest bones of the cranium; but enjoy the general structure of two tables and diploe the completest, and are the most equal and smooth.

These bones are joined at their fore-side to the os frontis by the coronal suture; at their long inferior angles, to the sphenoid bone, by part of the suture of this name; at their lower edge, to the os temporum, by the squamosus suture, and its posterior additamentum; behind, to the os occipitis, or osseae triquetra, by the lambdoid suture; and above, to one another, by the sagittal suture.

In a child born at the full time, none of the sides of this bone are completed; and there never is a hole in the ossified part of it near to the sagittal suture.

The large unossified ligamentous part of the cranium observable between the parietal bones, and the middle of the divided os frontis of new-born children, called by the vulgar the open of the head, was imagined by the ancients to serve for the evacuation of the superfluous moisture of the brain; and therefore they named it bregma, or the fountain; sometimes adding the epithet pulvinitis, or beating, on account of the pulsation of the brain felt through this flexible ligamento-cartilaginous substance. Hence very frequently the parietal bones are called osseae bregmatiae.

All the bregma is generally ossified before seven years of age. Several authors say, they have observed it unossified in adults; and physicians, who order the application of medicines at the meeting of the coronal and sagittal cal sutures, seem yet to think that a derivation of noxious humours from the encephalon is more easily procured at this part than any other of the skull; and that medicines have a greater effect here, than elsewhere, in the internal disorders of the head.

Ossa Temporum, so named, say authors, from the hair's first becoming grey on the temples, and thus discovering peoples ages, are each of them equal and smooth above, with a very thin semicircular edge; which, from the manner of its connection with the neighbouring bones, is distinguished by the name of os squamosum.—Behind this, the upper part of the temporal bone is thicker, and more unequal, and is sometimes described as a distinct part, under the name of pars mammillaris.—Towards the base of the skull, the temporal bone appears very irregular and unequal; and this part, instead of being broad, and placed perpendicularly, as the others are, is contracted into an oblong very hard substance, extended horizontally forwards and inwards, which in its progress becomes smaller, and is commonly called os petrosum.

Three external processes of each temporal bone are generally described.—The first, placed at the lower and hind-part of the bone, from its resemblance to a nipple, is called mastoides, or mammillaris. It is not solid, but within is composed of cancelli, or small cells, which have a communication with the large cavity of the ear, the drum; and therefore founds, being multiplied in this vaulted labyrinth, are increased, before they are applied to the immediate organ of hearing. Into the mastoid process, the stenomastoideus muscle is inserted; and to its back-part, where the surface is rough, the trachelo-mastoideus, and part of the splenius are fixed.—About an inch farther forward, the second process begins to rise out from the bone; and having its origin continued obliquely downwards and forwards for some way, it becomes smaller, and is stretched forwards to join with the os malae; they together forming the bony jugum, under which the temporal muscle passes. Hence this process has been named zygomatic. Its upper edge has the strong aponeurosis of the temporal muscle fixed into it; and its lower part gives rise to a share of the masseter.—The fore-part of the base of this process is an oblong tubercle, which in a recent subject is covered with a smooth polished cartilage, continued from that which lines the cavity immediately behind this tubercle.—From the under craggy part of the os temporum, the third process stands out obliquely forwards. The shape of it is generally said to resemble the ancient stylus scrip- torius; and therefore it is called the styloid process. Several muscles have their origin from this process, and borrow one half of their name from it; as stylo-glossus, stylo-hyoides, stylo-pharyngeus: to it a ligament of the os hyoides is sometimes fixed; and another is extended from it to the inside of the angle of the lower jaw. This process is often, even in adults, not entirely ossified, but is ligamentous at its root, and sometimes is composed of two or three distinct pieces.—Round the root of it, especially at the fore-part, there is a remarkable rising of the os petrosum, which some have effected a process; and, from the appearance it makes with the styloid form, have named it vaginalis.—Others again have, under the name of auditory process, reckoned among the external processes that semicircular ridge, which, running between the root of the mastoid and zygomatic processes, forms the under part of the external meatus auditorius.

The sinuities or depressions on the external surface of each os temporum are these:—A long fossa at the inner and back part of the root of the mammary process, where the posterior head of the digastric muscle has its origin.—Immediately before the root of the zygomatic process, a considerable hollow is left, for lodging the crotaphite muscle.—Between the zygomatic, auditory, and vaginal processes, a large cavity is formed; through the middle of which, from top to bottom, a fissure is observable, into which part of the ligament that secures the articulation of the lower jaw with this bone is fixed. The fore-part of the cavity being lined with the same cartilage which covers the tubercle before it, receives the condyle of the jaw; and in the back-part a small share of the parotid gland, and a cellular fatty substance, are lodged.—At the inside of the root of the styloid apophysis, there is a thimble-like cavity, where the beginning of the internal jugular vein, or end of the lateral sinus, is lodged.—Round the external meatus auditorius, several sinuities are formed for receiving the cartilages and ligaments of the ear, and for their firm adhesion.

The holes that commonly appear on the outside of each of these bones, and are proper to each of them, are five.—The first, situated between the zygomatic and mastoid processes, is the orifice of a large funnel-like canal, which leads to the organ of hearing; therefore is called meatus auditorius externus.—The second gives passage to the portio dura of the seventh pair of nerves; and, from its situation between the mastoid and styloid processes, is called foramen stylo mastoideum.—Some way before, and to the inside of the styloid process, is the third hole; the canal from which runs first upwards, then forwards, and receives into it the internal carotid artery, and the beginning of the intercostal nerve; where this canal is about to make the turn forwards, one, or sometimes two very small holes go off towards the cavity of the ear called tympanum: through these Valvalva affirms the proper artery or arteries of that cavity are sent.—On the anterior edge of this bone, near the former, a fourth hole is observable, being the orifice of a canal which runs outwards and backwards, in a horizontal direction, till it terminates in the tympanum. This, in the recent subject, is continued forward and inward, from the parts which were mentioned just now as its orifice in the skeleton, to the side of the nostrils: being partly cartilaginous, and partly ligamentous. The whole canal is named, Iter a palato ad aurem, or Eustachian tube.—On the external side of the bony part of this canal, and a-top of the chink in the cavity that receives the condyle of the lower jaw, is the course of the little nerve said commonly to be reflected from the lingual branch of the fifth pair, till it enters the tympanum, to run across this cavity, and to have the name of chorda tympani.—The fifth hole is very uncertain, appearing sometimes behind the mastoid process; sometimes it is common to the temporal and occipital bones; and in several skulls there is is no such hole. The use of it, when found, is for the transmission of a vein from the external teguments to the lateral sinus. But, in some subjects, a branch of the occipital artery passes through this hole, to serve the back-part of the dura mater.

The internal surface of the os temporum is unequal; the upper circular edge of the squamous part having numerous small ridges and furrows for its conjunction with the parietal bones; and the rest of it is irregularly marked with the convolutions of the middle part of the brain, and with furrows made by the branches of the arteries of the dura mater.

From the under part of this internal surface, a larger transverse, hard, craggy protuberance runs horizontally inwards and forwards, with a sharp edge above, and two flat sides, one facing obliquely forwards and outwards, and the other as much backwards and inwards. To the ridge between these two sides, the large lateral process of the dura mater is fixed.

Sometimes a small bone, akin to the sphenoid, is found between the small end of this petrous process and the sphenoid bone.

Towards the back-part of the inside of the os temporum, a large deep fossa is conspicuous, where the lateral sinus lies; and frequently on the top of the petrous ridge, a furrow may be observed, where a small sinus is situated.

The internal proper foramina of each of these bones are, first, the internal meatus auditorius in the posterior plain side of the petrous process. This hole soon divides into two; one of which is the beginning of the aqueduct of Falopius; the other ends in several very small canals, that allow a passage to the branches of the portio molis of the seventh pair of nerves, into the vestibule and cochlea. Through it also an artery is sent, to be distributed to the organ of hearing.—The second hole, which is on the anterior plain side of the craggy process, gives passage to a reflected branch of the second branch of the fifth pair of nerves, which joins the portio dura of the auditory nerve, while it is in the aqueduct, small branches of blood-vessels accompanying the nerves, or passing through smaller holes near this one.—The passage of the cutaneous vein into the lateral sinus, or of a branch of the occipital artery, is seen about the middle of the large fossa for that sinus; and the orifice of the canal of the carotid artery is evident at the under part of the point of the petrous process.

The upper round part of the squamous bones is thin, but equal; while the low petrous part is thick and strong, but irregular and unequal, having the dilution of tables and diploe confounded, with several cavities, processes, and bones within its substance, which are parts of the organ of hearing. See the description of the bones, muscles, &c. of the ear, in part VI.

The temporal bones are joined above to the parietal bones by the squamous sutures, and their posterior additamenta: Before, to the sphenoid bone by the future of that name; to the cheek-bones by the zygomatic sutures: Behind, to the occipital bone, by the lambdoid suture and its additamenta; and they are articulated with the lower jaw in the manner which shall be described when this bone is examined.

Os Occipitis, so called from its situation, is convex on the outside, and concave internally. Its figure is an irregular square, or rather rhomboid; of which the angle above is generally a little rounded; the two lateral angles are more finished, but obtuse; and the lower one is stretched forward in form of a wedge, and thence is called by some the cuneiform process.

The external surface is convex, except at the cuneiform apophyse, where it is flattened. At the base of this triangular process, on each side of the great hole, but more advanced forwards than the middle of it, the large oblong protuberances, named the condyles, appear, to serve for the articulation of this bone with the first vertebra of the neck. The smooth surface of each of these condyloid processes is longest from behind forwards, where, by their oblique situation, they come much nearer to each other than they are at their back-part. Their inner sides are lower than the external, by which they are prevented from sliding to either side out of the cavities of the first vertebra.—Round their root a small depression and spongy roughness is observable, where the ligaments for surrounding and securing their articulations adhere.—Though the motion of the head is performed on the condyles, yet the centre of gravity of that globe does not fall between them, but in a good way further forward; from which mechanism it is evident, that the muscles which pull the head back must be in a constant state of contraction: which is stronger than the natural contraction of the proper flexors, else the head would always fall forwards, as it does when a man is asleep, or labours under a palsy, as well as in infants, where the weight of the head far exceeds the proportional strength of these muscles.

All round the great foramen the edges are unequal, for the firmer adhesion of the strong circular ligament which goes thence to the first vertebra.—One end of each lateral or moderator ligament of the head, is fixed to a rough surface at the fore-part of each condyle, and the perpendicular one is connected to a rough part of the edge of the great hole between the two condyles.

On the inner surface of the os occipitis we see two ridges; one standing perpendicular, the other running horizontally across the first. The upper part of the perpendicular limb of the crest, to which the falx is fixed, is hollowed in the middle, or often on one side, for the reception of the superior longitudinal sinus, and the lower part of it has the small or third process of the dura mater fastened to it, and is sometimes hollowed by the occipital sinus. Each side of the horizontal limb is made hollow by the lateral fissures inclosed in the transverse process of the dura mater; the fossa in the right side being generally a continuation of the one made by the longitudinal sinus in the perpendicular limb, and therefore is larger than the left one.—Round the middle of the crest there are four large depressions separated by its limbs; the two upper ones being formed by the back-part of the brain, and the two lower ones by the cerebellum.—Farther forward than the last mentioned depressions, pressions, is the lower part of the fossa for the lateral sinus on each side.—The inner surface of the cuneiform apophysis is made concave for the reception of the medulla oblongata, and of the basilar artery.—A furrow is made on each side, near the edges of this process, by a sinus of the dura mater, which empties itself into the lateral sinus.

The holes of this bone are commonly five proper, and two common to it and to the temporal bones.—The first of the proper holes, called foramen magnum, from its size, is immediately behind the wedge-like process, and allows a passage to the medulla oblongata, nervi accessorii, to the vertebral arteries, and sometimes to the vertebral veins.—At each side of this great hole, near its fore-part, and immediately above the condyles, we always find a hole, sometimes two, which soon unite again into one that opens externally; through these the ninth pair of nerves go out of the skull.—The fourth and fifth holes pierce from behind the condyle of each side, into the fossae of the lateral sinuses; they serve for the passage of the cervical veins to these sinuses. Often one of these holes is wanting, sometimes both, when the veins pass through the great foramen.—Besides these five, we frequently meet with other holes near the edges of this bone, for the transmission of veins; but their number and diameter are very uncertain. The two common foramina are the large irregular holes, one in each side, between the sides of the cuneiform process, and the edges of the petrous bones. In a recent subject, a strong membrane runs across from one side to the other of each of these holes.

The occipital bone is among the thickest of the cranium, though unequally so; for it is stronger above, where it has no other defense than the common teguments, than it is below, where, being pressed by the lobes of the brain and cerebellum on one side, and, by the action of the muscles on the other, it is so very thin, as to be diaphanous in many skulls.

The occipital bone is joined above to the osseous parietalia and trigona when present, by the lambdoid suture;—laterally to the temporal bones, by the additamenta of the lambdoid suture;—below to the sphenoid bone, by the end of its cuneiform process, in the same way that epiphyses and their bones are joined.—The os occipitis is joined by a double articulation to the first vertebra of the neck, each condyle being received into a superior oblique process of that vertebra.

Os Ethmoides, or the sieve-like bone, has got its name from the great number of small holes with which that part of it first taken notice of is pierced. When this bone is entire, the figure of it is not easily described; but, by a detail of its several parts, some idea may be afforded of the whole; and therefore we shall distinguish it into the cribriform lamella with its processes, the nasal lamella, cellulae, and os spongiosum.

The thin horizontal lamella, is all (except its back-part) pierced obliquely by a great number of small holes, through which the filaments of the olfactory nerves pass.—From the middle of the internal side of this plate, a thick process rises upwards, and, being highest at the fore-part, gradually becomes lower, as it is extended backwards. From some resemblance which this process was imagined to have to a cock's comb, it has been called cribrum galli. The falx is connected to its ridge, and to the unperforated part of the cribriform plate.—When the cribrum is broke, its base is sometimes found to be hollow, with its cavity opening into the nose.

From the middle of the outer surface of the cribriform lamella, a thin fold plate is extended downwards and forwards, having the same common base with the cribrum galli. Generally it is not exactly perpendicular, but is inclined to one side or other, and therefore divides the cavity of the nose unequally. Its inclination to one side, and flexure in the middle, is sometimes so great, that it fills up a large share of one of the nostrils, and has been mistaken for a polypus there.—It is thin at its rife, and rather still thinner in its middle; yet afterwards, towards its lower edge, it becomes thicker, that its conjunction with the bones and middle cartilage of the nose might be firmer.

At a little distance from each side of this external process, a cellular and spongy bony substance depends from the cribriform plate. The number and figure of the cells in this irregular process of each side, are very uncertain; only the cells open into each other, and into the cavity of the nose: The uppermost, which are below the aperture of the frontal sinuses, are formed like funnels.—The outer surface of those cells is smooth and plain, where this bone affords in composing the orbit; at which place, on each side, it has got the name of os planum; on the upper edge of which, a small notch or two may sometimes be observed, which go to the formation of the internal orbital holes.

Below the cells of each side, a thin plate is extended inwards, and then bending down, it becomes thick, and of a spongy texture.—This spongy part is triangular, with a straight upper edge placed horizontally, an anterior one slanting from above, downwards and forwards, and with a pendulous convex one below.—The upper and lower edges terminate in a sharp point behind.—The side of this pendulous spongy part next to the septum narium is convex, and its external side is concave.—These two processes of the ethmoid bone have got the name of os spongiosum, or turbinate superiora, from their substance, figure, and situation.

All the prominences, cavities and meanders of this ethmoid bone, are covered with a continuation of the membrane of the nostrils, in a recent subject.—Its horizontal cribriform plate is lodged between the orbital processes of the frontal bone, to which it is joined by the ethmoid suture, except at the back-part, where it is connected with the cuneiform bone, by a suture common to both these bones.—Where the os planum are contiguous to the frontal bone within the orbit, their conjunction is reckoned part of the transverse suture.—Farther forward than the os planum, the cells are covered by the osseous uncus, which are not only contiguous to these cells, but cannot be separated from them, without breaking the bony substance.—Below the osseous uncus and plana, these cells and os spongiosum are overlapped by the maxillary bones.—The cellular part of each palate-bone is contiguous to each os planum and cells backwards.—The Lower edge of the nasal perpendicular plate is received into the furrow of the vomer.—Its posterior edge is joined to the fore-part of the processus azygos of the sphenoid bone.—Its upper edge joins the nasal processes of the frontal and nasal bones, and its anterior one is connected to the middle cartilage of the nose.

From all which the uses of this bone are evident, viz. to sustain the anterior lobes of the brain; to give passage to the olfactory nerves, and attachment to the falx; to enlarge the organ of smelling, by allowing the membrane of the nose a great extent; to straighten the passage of the air through the nose, by leaving only a narrow winding canal, on the sensible membranous sides of which the substances conveyed along with the air must strike, to form part of the orbit of the eyes and septum narium; while all its parts are so light as not to be in hazard of separating by their weight; and they are so thin, as to form a large surface, without occupying much space.

Os Sphenoides, or wedge-like bone, so called because of its situation in the middle of the bones of the cranium and face, is of an irregular figure, and bears some faint resemblance to a bat with its wings extended.

When we view the external surface of the os sphenoides, two or three remarkable processes from each side of it may be observed; which are all of them again subdivided.—The first pair is the two large lateral processes or wings; the upper part of each of which is called the temporal process, because they join with the temporal bones in forming the temples, and the seat for some share of the crotaphite muscles. That part of the wings which juts out towards the inside, somewhat lower than the temporal apophyses, and is smooth and hollowed, where it makes up part of the orbit, is thence named orbital processes. Behind the edge separating these two processes, there is often a small groove, made by a branch of the superior maxillary nerve, in its passage to the temporal muscle. The lowest and back-part of each wing, which runs out sharp to meet the osse petrosum, has been styled the spinous process; from near the point of which a sharp pointed process is frequently produced downwards, which some call styliform, that affords origin to the pterygoid muscles. From this styloid process a very small groove is extended along the edge of the bone to the hollow at the root of the internal plate of the following processes, which forms part of the Eustachian tube.—The second pair of external processes of the cuneiform bone is the two which stand out almost perpendicular to the base of the skull. Each of them has two plates, and a middle fossa facing backwards, and are named pterygoid or aliform processes. The external plates are broadest, and the internal are longest. From each side of the external plates, the pterygoid muscles take their rise. At the root of each internal plate, a small hollow may be remarked, where the musculus pterygoides internus, or circumflexus palati, rises, and some share of the cartilaginous end of the Eustachian tube rests; and, at the lower end of the same plate, is a hook-like rising or process, round which the tendon of the last named muscle plays, as on a pulley.

To these another pair may be added, to wit, the little triangular thin process, which comes from each side of the body of the sphenoid bone, where the pterygoid processes are rising from it, and are extended over the lower part of the aperture of the sinus, as far as to join the ethmoid bone, while their body hangs down into the nares.—Besides these pairs of processes, there is a sharp ridge which stands out from the middle of its base: Because it wants a fellow, it may be called processus azygos. The lower part of this process, where it is received into the vomer, is thick, and often not quite perpendicular, but inclining more to one side than the other. The fore-part of this process, where it joins the nasal plate of the os ethmoides, is thin and straight.

The depressions, sinuositys, and fossae, on the external surface of this sphenoid bone, may be reckoned up to a great number, viz. two on the temporal apophyses where the crotaphite muscles lodge.—Two on the orbital processes, to make way for the globes of the eyes.—Two between the temporal and spinous processes, for receiving the temporal bones.—Two between the plates of the pterygoid processes, where the musculi pterygoidei interni and pterygoides interni are placed.—Two between the pterygoid and orbital processes, for forming the holes common to this and to the cheek and maxillary bones.—Two on the lower ends of the aliform processes, which the palate-bones enter into.—Two at the roots of the temporal and pterygoid processes, where the largest share of the external pterygoid muscles have their rise.—Two at the sides of the processus azygos, for forming part of the nose, &c.

What was described under the name of temporal and spinous processes on the outside of the skull, are likewise seen on its inside, where they are concave, for receiving part of the brain; and commonly three apophyses on the internal surface of the sphenoid bone are only mentioned.—Two rising broad from the fore-part of its body, become smaller, as they are extended obliquely backwards.—The third standing on a long transverse base, near the back-part of the body of this bone, rises nearly erect, and of an equal breadth, terminating often in a little knob on each side. The three are called clinoid, from some resemblance which they were thought to have to the supporters of a bed.—From the roots of the anterior clinoid processes, the bone is extended on each side outwards and forwards, till it ends in a sharp point, which may have the name of the transverse spinous processes.—Between, but a little farther back than the two anterior clinoid processes, we see a protuberance considerably smaller than the posterior clinoid process, but of its shape.—Another process from between the transverse processes, often forces itself forwards into the os ethmoides.

Within the skull, there are two sinuosities in the internal part of each wing of the sphenoid bone, for receiving the middle part of the brain.—One between the transverse spinous processes, for lodging the part of the brain where the crura medullae oblongatae are.—Immediately before the third or middle clinoid process, a single pit generally may be remarked, from which a fossa goes out on each side to the holes through which the optic nerves pass. The pit is formed by the conjoined optic nerves; and in the fossa these nerves are lodged, as they run divided within the skull.—Between that third protuberance and the posterior clinoid process, the larger pit for the glandula pituitaria may be remarked. This cavity, because of its resemblance to a Turkish saddle, is always described under the name of sella Turcica, or epiphysium.—On the sides of the posterior clinoid process a fossa may be remarked, that stretches upwards, then is continued forwards along the sides of the sella Turcica, near to the anterior clinoid processes, where a pit on each side is made. These fossae point out the course of the two internal carotid arteries, after they have entered the skull.

The holes on each side of the os sphenoides are six proper, and three common.—The first is the round one immediately below the anterior clinoid processes, for the passage of the optic nerve, and of the branch of the internal carotid artery that is sent to the eye.—The second is the foramen lacerum, or large slit between the transverse spinous and orbital processes; Through it the third, fourth, the first branch of the fifth, and the greater share of the sixth pair of nerves, and an artery from the internal carotid, go into the orbit. Sometimes a small branch of the external carotid enters near its end, to be distributed to the dura mater, and a vein, some call it the venous duct, or Nuck's aqueduct, returns through it to the cavernous sinus.—The third hole, situated a little below the one just now described, is called rotundum, from its shape. It allows passage to the second branch of the fifth pair of nerves, or superior maxillary nerve, into the bottom of the orbit.—The fourth is the foramen ovale, about half an inch behind the round hole. Through it the third branch of the fifth pair, or inferior maxillary nerve, goes out; and sometimes a vein from the dura mater passes out here.—Very near the point of the spinous process is the fifth hole of this bone: It is small and round, for a passage to the largest artery of the dura mater, which often is accompanied with a vein.—The sixth proper hole cannot be well seen, till the cuneiform bone is separated from all the other bones of the cranium; for one end of it is hid by a small protuberance of the internal plate of the pterygoid process, and by the point of the processus petrosus of the temporal bone. Its canal is extended above the inner plate of the pterygoid process; and where it opens into the cavity of the nose, it is concealed by the thin laminae part of the palate-bone. Through it a considerable branch of the second branch of the fifth pair of nerves is reflected.—Often in the middle of the sella Turcica, a small hole or two pierce as far as the cellular substance of the bone; and sometimes at the sides of this sella, one or more small holes penetrate into the sphenoidal sinuses.

The first of the common holes is that unequal fissure at the side of the sella Turcica, between the extreme point of the os petrosum and the spinous process of the cuneiform bone.—The second common hole is the large discontinuation of the external side of the orbit, left between the orbital processes of the cuneiform bone, the os maxillare, male, and palati. In this large hole the fat for lubricating the globe of the eye and temporal muscle is lodged, and branches of the superior maxillary nerve, with small arteries from the carotid and veins, pass.

—The third hole is formed between the base of this bone and the root of the orbital process of the palate-bone of each side. Through this a branch of the external carotid artery, and of the second branch of the fifth pair of nerves, are allowed a passage to the nostrils, and a returning vein accompanies them.

Under the sella Turcica, and some way farther forward, but within the substance of the sphenoid bone, are two sinuses, separated by a bony plate. Each of them is lined with a membrane, and opens into the upper and back part of each nostril by a round hole, which is at their upper fore-part. This hole is not formed only by the os sphenoides, which has an aperture near as large as any transverse section of the sinus, but also by the palate-bones which are applied to the fore-part of these sinuses, and close them up, that hole only excepted, which was already mentioned. Frequently the two sinuses are of unequal dimensions, and sometimes there is only one large cavity, with an opening into one nostril.

As this bone is extremely ragged and unequal, so its substance is of very different thickness, being in some places diaphanous; in others it is of a middle thickness, and its middle back-part surpasses the greatest share of the cranium in thickness.

The os sphenoides is joined, by its wings, to the parietal bones above, to the os frontis and osa malarum before, to the temporal bones behind;—by the fore-part of its body and spinous processes, to the frontal and ethmoid bones;—by its back-part, behind the two sinuses, to the occipital, where it looks like a bone with the epiphyses taken off;—to the palate-bones, by the ends of the pterygoid processes, and still more by the fore-part of the internal plates of the pterygoid processes, and of the sinuses;—to the maxillary bones, by the fore-part of the external pterygoid plates;—to the vomer and nasal plate of the os ethmoides, by the processus azygos. All these conjunctions, except the last, which is a chondylesis, are said to be by the future proper to this bone; though it is at first sight evident, that several other futures, as the transverse, ethmoidal, &c. are confounded with it.

We see now how this bone is joined to all the bones of the cranium, and to most of the upper jaw; and therefore obtained the name of the wedge-like bone.

The Face is the irregular pile of bones, composing the fore and under part of the head, which is divided into the upper and lower maxillæ or jaws.

The superior maxilla is the common designation given to the upper immovable share of the face. The shape of the superior jaw cannot easily be expressed; nor is it necessary, provided the shape and situation of all the bones which compose it are described. It is bounded above by the transverse future, behind by the fore-part of the sphenoid bone, and below by the mouth.

The upper jaw consists of six bones on each side, of a thirteenth bone which has no fellow, placed in the middle, and of sixteen teeth. The thirteen bones are, two osa naso, two osa unguis, two osa malarum, two osa maxillaria, two osa palati, two osa spongiosa inferiora, and the vomer. The ossa nasai are placed at the upper part of the nose; —the osa unguis are at the internal canthi of the orbits; —ossa malarum form the prominence of the cheeks; —ossa maxillaria form the side of the nose, with the whole lower and fore part of the upper jaw, and the greatest share of the roof of the mouth; —ossa palati are situated at the back-part of the palate, nostrils, and orbit; —ossa spongiosa are seen in the lower part of the nares; —and the vomer helps to separate these two cavities.

The bones of the upper jaw are joined to the bones of the skull by the schindylefs and sutures already described as common to the cranium and face, and they are connected to each other by gomphosis and fifteen sutures.

The gomphosis only is where the teeth are fixed in their sockets, and the schindylefs is only where the edges of the vomer are joined to other bones.

The first is the anterior nasal, which is straight, and placed longitudinally in the middle fore-part of the nose.

The second and third are the lateral nasal, which are at each side of the nose, and almost parallel to the first suture.

Each of the two lacrymal is almost semicircular, and is placed round the lacrymal groove.

The fifth and seventh are the internal orbital: each of which is extended obliquely from the middle of the lower side of an orbit to the edge of its base.

The two external orbitars are continued, each from the end of the internal orbital, to the under and fore-part of the cheek.

The tenth is the mylohyal, which reaches only from the lower part of the septum narium to between the two middle denticles incisores.

The longitudinal palate suture stretches from the middle of the foremost teeth through the middle of all the palate.

The transverse palate one runs across the palate, nearer the back than the fore-part of it.

Each of the two palato-maxillary is at the back-part of the side of each nostril.

The fifteenth is the spinous, which is in the middle of the lower part of the nostrils. This may perhaps be rather thought a double schindylefs.

These sutures of the face have not such conspicuous indentations as those of the skull have.

Ossa Nasai, so named from their situation at the root of the nose, are each of an irregular oblong square figure, being broadest at their lower end, narrowest a little higher than their middle; and becoming somewhat larger at the top, where they are ragged and thickest, and have a curvature forwards, that their connection with the frontal bone might be stronger. —These bones are convex externally, and thereby better resist any violence from without; and they are concave internally, for enlarging the cavity of the nose.

The lower edge of these bones is unequal, and is stretched outwards and backwards, to join the cartilages of the nostrils. —Their anterior side is thick, especially above, and unequal, that their conjunction to each other might be stronger; and a small rising may be remarked on their inner edge, where they are sustained by the septum narium. —Their posterior side, at its upper half, has externally a depression, where it is overlapped some way by the maxillary bones, while its lower half covers these bones: By which contrivance, they do not yield easily to pressure applied to their fore-part or sides.

A small hole is frequently to be observed on their external surface, into which two, three, or four holes, which appear internally, terminate for the transmission of small veins; sometimes the holes go no farther than the cancelli of the bones.

The nasal bones are firm and solid, with very few cells or cancelli in them.

They are joined above to the frontal bone, by the middle of the transverse suture; —behind, to the maxillary bones, by the lateral nasal sutures; —below, to the cartilages of the nose; —before to one another, by the anterior nasal suture; —internally, to the septum narium.

These bones serve to cover and defend the root of the nose.

Ossa Unguis, or Lacrymalia, are so named, because their figure and magnitude are something near to those of a nail of one's finger, and because the tears pass upon them into the nose.

Their external surface is composed of two smooth cavities and a middle ridge. —The depression behind forms a small share of the orbit for the eye-ball to move on, and the one before is a deep perpendicular canal, or fossa, larger above than below, containing part of the lacrymal sac and duct. This is the part that ought to be pierced in the great operation for the fistula lacrymalis. —This fossa of the bone is cribriform, or has a great number of small holes through it, that the filaments from the membrane which lines it, infusing themselves into these holes, might prevent a separation of the membrane, and secure the bone in its natural situation. —The ridge between these two cavities of the os unguis, is the proper boundary of the orbit at its internal canthus; and beyond which surgeons should not proceed backwards in performing operations here. —The internal or posterior surface of this bone consists of a furrow in the middle of two convexities.

The substance of the os unguis is as thin as paper, and very brittle; which is the reason that these bones are often wanting in skeletons, and need little force to pierce them in living subjects.

Each of these bones is joined, above, to the frontal bone, by part of the transverse suture; —behind, to the os planum of the ethmoid bone, by the same suture; —before, and below, to the maxillary bone, by the lacrymal suture; —internally, the osa unguis cover some of the sinus ethmoidales.

These ungualiform bones compose the anterior internal parts of the orbits, lodge a share of the lacrymal sac and duct, and cover the ethmoid cells. —Their situation and tender substance make a rash operator in danger of destroying a considerable share of the organ of smelling, when he is performing the operation of the fistula lacrymalis.

Ossa Malarum are the prominent square bones which form the cheek on each side. —Before, their sur- face is convex and smooth; backward, it is unequal and concave, for lodging part of the crotaphyte muscles.

The four angles of each of these bones have been reckoned processes by some. — The one at the external canthus of the orbit, called the superior orbital process, is the longest and thickest. — The second terminates near the middle of the lower edge of the orbit in a sharp point, and is named the inferior orbital process. — The third, placed near the lower part of the cheek, and thence called maxillary, is the shortest, and nearest to a right angle. — The fourth, which is called zygomatic, because it is extended backwards to the zygoma of the temporal bone, ends in a point, and has one side straight, and the other slopping. — Between the two orbital angles there is a concave arch, which makes about a third of the external circumference of the orbit, from which a fifth process is extended backwards within the orbit, to form near one third of that cavity; and hence it may be called the internal orbital process. — From the lower edge of each of the osa malarum, which is between the maxillary and zygomatic processes, the masseter muscle takes its origin; and from the exterior part of the zygomatic process, the musculus dilator oris rises; in both which places the surface of the bone is rough.

On the external surface of each cheek bone, one or more small holes are commonly found, for the transmission of small nerves or blood-vessels from, and sometimes into the orbit. — On the internal surface are the holes for the passage of the nutritious vessels of these bones. — A notch on the outside of the internal orbital process of each of these bones affords to form the great slit common to this bone and to the sphenoid, maxillary, and palate-bones.

The substance of these bones is, in proportion to their bulk, thick, hard, and solid, with some cancelli.

Each of the osa malarum is joined, by its superior and internal orbital processes, to the os frontis, and to the orbital process of the sphenoid bone, by the transverse suture. — By the edge between the internal and inferior orbital processes, to the maxillary bone, by the internal orbital suture. — By the side between the maxillary and inferior orbital process, again to the maxillary bone, by the external orbital suture. — By the zygomatic process, to the os temporum, by the zygomatic suture.

Ossa Maxillaria Superiora, are the largest bones, and constitute the far greater part of the upper jaw.

The processes of each os maxillare may be reckoned seven. — The first is the long nasal one at its upper and fore-part, which is broad below, and turns smaller, as it rises upwards, to make the side of the nose. — At the root of this, a transverse ridge may be observed within the nostrils, which supports the fore-part of the upper edge of the os spongiosum inferius. — The second is produced backwards and outwards, from the root of the nasal process, to form the lower side of the orbit; and therefore may be called orbital. — The edge of this orbital process, and the ridge of the nasal one, which is continued from it, make a considerable portion of the external circumference of the orbit. — From the proper orbital process, a very rough triangular surface is extended downwards and outwards, to be connected to the cheekbone; and therefore may be called the malar process, from the lowest protuberant part of which some share of the malar muscle takes its rise. — Behind the orbital process, a large tuberosity or bulge of the bone appears, which is esteemed the fourth process. — On the internal part of this we often meet with a ridge, almost of the same height with that in the nasal process, which runs transversely, and is covered by a similar ridge of the palate-bone, on which the back-part of the upper edge of the os spongiosum inferius rests. — The convex back-part of this tuberosity is rough for the origin of part of the external pterygoid muscle, and more internally is scabrous, where the palate and sphenoid bones are joined to it. — That spongy protuberance at the lower circumference of this bone, where the sockets for the teeth are formed, is reckoned the fifth. — The sixth is the horizontal plate, which forms the greater part of the base of the nostrils, and roof of the mouth; its upper surface, which belongs to the nostrils, is very smooth, but the other below is arched and rough, for the stronger adhesion of the membrane of the mouth, which is stretched upon it, and in chewing, speaking, &c., might otherwise be liable to be separated. — The seventh rises like a spine from the inner edge of the last, and forms a small part of the partition of the nostrils.

The depressions in each maxillary bone are, 1. A sinusosity behind the orbital process, made by the temporal muscle. 2. A pit immediately before the same process, where the origin of the musculus elevator labiorum communis, and elevator labii superioris, with a branch of the fifth pair of nerves, are lodged securely. 3. The hollow arch of the palate. 4. The semicircular great notch, or entry to the lower part of the nostrils, betwixt the root of the nasal process and spine of the palate-plate. 5. Sockets for the teeth: The number of these sockets is uncertain. 6. The lacrymal fossa in the nasal process, which affords the os unguis to form a passage for the lacrymal duct. Immediately on the outside of this, there is a small depression, from which the inferior or lesser oblique muscle of the eye has its origin. 7. The canal on the upper part of the great tuberosity within the orbit, which is almost a complete hole; in this a branch of the superior maxillary nerve passes. Besides these, the superior surface of the great bulge is concave, to receive the under part of the eye. — Immediately above the transverse ridge in the nasal process, a small hollow is formed by the os spongiosum.

The holes of this bone are two proper and two common, which are always to be found, besides several others, whose magnitude, number, &c., are uncertain. — The first of the proper is the external orbital, immediately below the orbit, by which the infra-orbital branch of the second branch of the fifth pair of nerves, and a small artery, come out, after having passed in the canal, at the bottom of the orbit, described Numb. 7. of the depressions. — The second is the foramen incisivum, just behind the fore-teeth, which, at its under part, is one irregular hole common to both the maxillary bones when they are joined; but, as it ascends, soon divides into two, three, or sometimes more holes; some of which open into each nostril. Through them small arteries and veins, and a twig of the second branch of the fifth pair of nerves pass, and make a communication between, or join the lining coats of the nose and mouth.

The first common hole is that which appears at the inner side of the back-part of the tuberosity and of the sockets of the teeth, and is formed by a fossa in this bone, and a corresponding one in the os palati: through it a nerve, which is a branch of the second branch of the fifth pair, runs to the palate.—The other common hole is the great slit in the outside of the orbit described already, as the second common hole of the sphenoid bone.

All the body of the maxillary bone is hollow, and leaves a large sinus akin to the frontal and sphenoid, which is commonly, but unjustly, called antrum Highmorianum.—At the bottom of this cavity, we may often observe some protuberances, in which the small points of the roots of the teeth are contained.—This cavern and the sockets of the teeth are often divided by the interposition only of a very thin bony plate, which is liable to be eroded by acrid matter collected in the antrum, or to be broke in drawing a tooth. The symptoms of a collection of a matter here naturally lead us to the practice of pulling out the teeth, and piercing through this plate into the antrum, to procure an evacuation of the collected matter.

The maxillary sinuses have the same uses as the frontal and sphenoidal; and the situation of the sinuses is such, that the liquor drilling from them, from the cells of the ethmoid and palate-bones, and from the lacrymal ducts, may always moisten all the parts of the membrane of the nares in the different situations which the head is in.

The substance of the osseum maxillaria is compact and firm, except at the inferior processes, in which the teeth are lodged, where it is very spongy.

The maxillary bones are joined above by the upper ends of their nasal processes to the os frontis, by the transverse future;—at the sides of these processes, to the os unguis, by the lacrymal futures;—to the nasal bones, by the lateral nasal futures;—by their orbital processes, to the cheek-bones, by the external orbital futures;—by the internal sides of the internal orbital processes, to the os plana, by part of the ethmoidal future;—by the back-part of the tuberosities, to the palate bones, by the futura palato-maxillares;—by the posterior edges of their palatine lamellae, to the os palati, by the transverse palate-future;—by their nasal spines, to the vomer, by the spinous future;—by their sockets, to the teeth by gomphosis;—by the internal edge of the palate-plate, to one another, by the longitudinal palate-future; on the upper and fore-part of which a furrow is left for receiving the cartilage which forms the partition of the nostrils;—between the fore-part of the nostrils and mouth, to each other, by the mystacial future;—sometimes they are connected to the os spongionia inferiore, by a plain concretion or union of substance.

These bones form the greater part of the nose and of the roof of the mouth, and a considerable share of the orbit. They contain fifteen teeth, give rise to muscles, transmission to nerves, &c., as mentioned in the description of their several parts.

Osse Palati are commonly described as two small square bones, at the back-part of the palate or roof of the mouth, though they are of much greater extent, being continued up the back-part of the nostrils to the orbit. Each palate-bone may therefore be divided into four parts, the palate square bone, the pterygoid process, nasal lamella, and orbital process.

The square bone is unequally concave, for enlarging both the mouth and cavity of the nose. The upper part of its internal edge rises in a spine, after the same manner as the palate-plate of the maxillary bone does, to be joined with the vomer.—Its anterior edge is unequally ragged, for its firmer connexion with the palate-process of the os maxillare.—The internal edge is thicker than the rest, and of an equal surface, for its conjunction with its fellow of the other side.—Behind, this bone is somewhat in form of a crescent, and thick, for the firm connection of the velum pendulum palati; the internal point being produced backwards, to afford origin to the palato-staphylinus, or azygos-muscle.—This square bone is well distinguished from the pterygoid process by a perpendicular fossa, which, applied to such another in the maxillary bone, forms a passage for the palatine branch of the fifth pair of nerves; and by another small hole behind this, through which a twig of the same nerve passes.

The pterygoid process is somewhat triangular, having a broad base, and ending smaller above. The back-part of this process has three fossae formed in it; the two lateral receive the ends of the two plates of the sphenoid bone, that are commonly compared to a bat's wing; the middle fossa makes up a part of what is commonly called the fossa pterygoidea; the fore-side of this palatine pterygoid process is an irregular concave, where it receives the back-part of the great tuberosity of the maxillary bone.—Frequently several small holes may be observed in this triangular process, particularly one near the middle of its base, which, a little above, communicates with the common and proper holes of this bone already taken notice of.

The nasal lamella of this bone is extremely thin and brittle, and rises upwards from the upper side of the external edge of the square bone, and from the narrow extremity of the pterygoid process; where it is so weak, and at the same time so firmly fixed to the maxillary bone, as to be very liable to be broken in separating the bones.—From the part where the plate rises, it runs up broad on the inside of the tuberosity of the maxillary bone, to form a considerable share of the sides of the maxillary sinus, and to close up the space between the sphenoid and the great bulge of the maxillary bone, where there would otherwise be a large slit opening into the nostrils. From the middle internal side of this thin plate, a crofs ridge, placed on such another of the maxillary bone, is extended; on it the back-part of the os spongionium Along the outside of this plate, the perpendicular fossa made by the palate-nerve is observable.

At the upper part of this nasal plate, the palate-bone divides into two processes, which were already named orbital; between which and the body of the sphenoid bone, that hole is formed, which was mentioned as the last of the holes common to the sphenoid bone. Sometimes this hole is wholly formed in the os palati, by a crofs plate going from the one orbital process to the other. A nerve, artery, and vein belonging to the nostrils, pass here. The anterior of the two orbital processes is the largest, and has its fore-part contiguous to the back-part of the maxillary sinus, and its upper surface appears in the bottom of the orbit, behind the back-part of the os maxillare and planum. It has cells behind, resembling those of the ethmoid bone, to which it is contiguous; it is placed on the aperture of the sinus sphenoidalis, so as to leave only a round hole at its upper fore-part. The other part of the orbital process is extended along the internal side of the upper back-part of the maxillary tuberosity, to the base of the sphenoid bone, between the root of the processus azygos and the pterygoid process.

The palate-bones are joined to the maxillary, by the fore-edge of the palate square-bone, by the transverse palate-future; by their thin nasal plates, and part of their orbital processes, to the same bones, by the palato-maxillares futures; by their pterygoid processes, and back-part of the nasal plates, to the alae vesperilio-nun, by the sphenoid future; by the transverse ridges of the nasal plates, to the os spongiosum inferiora, by contact; hence frequently there is an intimate union of the substance of these bones in old skulls; by the orbital processes, to the os plana and cellula ethmoidex, by the ethmoid future; to the body of the sphenoid bone, by the sphenoid future; by the internal edge of the square-bones, to each other, by the longitudinal palate-future; and by their nasal spines, to the vomer, by the spinous future.

The palate-bones form part of the palate, nostrils, orbits, and fossa pterygoidea, and they cover part of the sinus maxillares, sphenoidales, and ethmoides.

Ossa Turbinata, or spongiosa inferiora, resemble the superior osa spongiosa in shape and substance, but have their anterior and upper edges contiguous to the transverse ridges of the nasal processes of the maxillary and palate-bones. From their upper straight edge, two small processes stand out: the posterior, which is the broadest, descends to cover some of the antrum Highmo-ranium; the anterior rises up to join the os ungus, and to make part of the lacrimal duct.

Below the spongy bones already mentioned, there are sometimes two others, one in each nostril, which seem to be a production of the sides of the maxillary sinus turned downwards. When this third sort of spongy bones is found, the middle one of the three in each nostril is the largest, and the lowest is the smallest. Besides all these, there are often several other small bones standing out into the nostrils, that, from their shape, might also deserve the name of turbinata, but are uncertain in their bulk, situation, and number.

They are joined to the osa maxillaria, palati, and unguis, especially in old subjects.

Their use is, to straighten the nostrils, to afford a large surface for extending the organ of smelling, to cover part of the antra maxillaria, and to assist in forming the under part of the lacrymal ducts, the orifices of which into the nose are concealed by these bones.

Vomer, or bone resembling a ploughshare, is the thirteenth of the upper jaw, without a fellow, forming the lower and back-parts of the partition of the nose.

The figure of this bone is an irregular rhomboid. Its sides are flat and smooth. Its posterior edge appears in an oblique direction at the back-part of the nostrils. The upper one is firmly united to the base of the sphenoid bone, and to the nasal plate of the ethmoid; and, when it can be got separated, is hollow, for receiving the processus azygos of the sphenoid. The anterior edge has a long furrow in it, where the middle cartilage of the nose enters. The lower edge is firmly united to the nasal spines of the maxillary and palate-bones. These edges of this bone are much thicker than its middle, which is as thin as the finest paper.

Its situation is not always perpendicular, but often inclined and bended to one side, as well as the nasal plate of the ethmoid-bone.

The vomer is convex at its upper part, and then is straight as it is extended downwards and forwards, where it is composed of two plates; the edges of which have a great number of small processes, disposed somewhat like the teeth of a saw, but more irregularly, and several of them are reflected back. Between these plates, a deep fossa is left, which, so far as the top of the curvature, is wide, and has strong sides, for receiving the processus azygos of the sphenoid-bone. Beyond the arch forwards, the fossa is narrower and shallower gradually to the point of the bone, receiving for some way the nasal lamella ethmoidica, which is so closely united to the vomer, by the little processes piercing into its substance, as to prevent any separation. The middle cartilage of the nose fills up what remains of the fossa at its fore-part.

The posterior edge of the vomer, which appears above the back-part of the palate-bones, is broader above; but as it extends forwards, becomes thinner, though it is still solid and firm. The lower edge of this bone, which rests on the nasal spine of the palate and maxillary bones, has a little furrow on each side, of a small middle ridge, answering to the spines of the bones of different sides, and the interstice between them. This edge and the upper one meet in the pointed fore-end of this bone.

The body of the vomer has a smooth surface, and solid, but thin substance; and towards its sides, where it is thickest, some cancelli may be observed, when the bone is broken.

It is joined above to the sphenoid and ethmoid bones, and to the middle cartilage of the nose, by schindyloids; below, to the maxillary and palate-bones, by the spinous future. The vomer divides the nostrils, enlarges the organ of smelling, by allowing place for expanding the membrane of the nose on its sides, and sustains the palate-plates of the maxillary and palate-bones.

Maxilla Inferior, the lower jaw, consists only of one moveable bone, and fifteen teeth incased into it.

This bone, which is somewhat of the figure of the Greek letter v, is situated at the lower part of the face, so as its convex middle part is forwards, and its legs are stretched back. It is commonly divided into the chin, sides, and processes. The chin is the middle fore-part, the extent of which to each side is marked on the external surface by the holes observable there, and internally, by the beginning of an oblique ridge. Beyond these, the sides appear, and are continued till the bone, by bending upwards, begins to form the processes.

On the fore-part of the chin, a transverse ridge appears in the middle, on each side of which the musculi quadrati, or depressores labii inferioris, and the levatores labii inferioris, depress the bone: And below these prints, a small rising may be observed, where the depressores commence.—On the back-part of the chin, sometimes three, always two, small protuberances appear in the middle. To the uppermost, when it is seen, the frenum of the tongue is connected. From the middle one, the musculi genioglossi rise; and from the lowest, the geniohyoidei have their origin.

At the lower and fore-part of the external surface of each side of the lower jaw, a small eminence may be observed, where the depressor labiorum communis rises. Near the upper edge of the side a ridge runs length-ways, to which the under part of the musculus buccinator is connected.—Internally, towards the upper edge of each side, another ridge appears, from which the mylohyoidei have their origin, and to which the internal membrane of the gums adheres.

In the upper edge of both chin and sides are a great many deep pits or foci, for receiving the roots of the teeth. The number and magnitude of these sockets are various, because of the different number, as well of the teeth themselves, as of their roots, in different people. These foci in this lower jaw, as well as in the upper one, are less deep as old age comes on; when freed from the teeth by any means, they are some time after filled up with an osseous net-work, which at last becomes entirely solid, and as smooth as any other part of the bone; so that in a great many old jaws, one cannot observe a vestige of the foci. But then the jaw becomes less, and much narrower.—Hence we may know why the chin and nose of edentulous people are much nearer than before the teeth were lost; while their lips either fall in towards the mouth, or stand prominent forwards.—When new teeth are protruded, new foci are formed.

The lower edge of the chin and sides is smooth and equal, and is commonly called the base of the lower jaw. The ends of the base, where the jaw turns upwards, are called its angles; the external surface of each of which has several inequalities upon it, where the masticator muscle is inserted; as the internal surface also has, where the pterygoideus internus is inserted, and a ligament, extended from the styloid process of the temporal bone, is fixed.

The processes are two on each side.—The anterior sharp thin coronoid ones have the crotaphytes muscles inserted into them.—The posterior processes, or condyles, terminate in an oblong smooth head, supported by a cervix. The heads, whose greatest length is transverse, and whose convexity is turned forwards, are tipped with a cartilage, as the articulated parts of all other moved bones are.—The fore-part of the root and neck of these condyloid processes are a little hollow and rough, where the external pterygoid muscles are inserted.

The holes of the lower jaw are two on each side; one at the root of the processes internally, where a large branch of the third branch of the fifth pair of nerves enters with an artery, and a vein returns. A small sharp process frequently juts out backwards from the edge at the fore-part of this hole, to which a ligament, extended from the temporal bone, is fixed, which saves the nerve and vessels from being too much pressed by the pterygoid muscles.—From the lower side of this hole, either a small superficial canal or a furrow descends, where a branch of the nerve is lodged, in its way to the mylohyoideus muscle and sublingual gland.—The other hole is external, at the confines of the chin, where branches of the nerve and vessels come out.—The canal betwixt these two holes is formed in the middle of the substance of the bone, and is pierced by a great number of small holes by which the nerves and blood-vessels of the cancelli and teeth pass.

The lower jaw generally receives the roots of sixteen teeth into its foci, by gonophosis; and its condyloid processes, covered with cartilage, are articulated with the temporal bones.

The Teeth are the hard white bodies placed in the foci of both jaws. Their number is generally sixteen above, and as many below; though some people have more, others have fewer.

The broad thick part of each tooth which appears without the focus, is the base, or body.—The smaller processes sunk into the maxilla, are the roots or fangs, which become gradually smaller towards the end fartherest from the base, or are nearly conical, by which the surface of their sides divides the pressure made on the bases, to prevent the soft parts, which are at the small points of the foci, to be hurt by such pressure.

Without the gums the teeth are covered with no membrane, and they are said to have no proper periosteum within the foci; but that is supplied by the reflected membrane of the gums; which, after a good injection, may be evidently seen in a young subject, with the vessels from it penetrating into the substance of the teeth; and it may be discovered in any tooth recently pulled, by macerating it in water. The adhesion of this membrane to these roots is strengthened by the small furrows observable on them.

Each tooth is composed of its cortex, or enamel, and an internal bony substance. The cortex has no cavity or place for marrow; and is so solid and hard, that saws or files can with difficulty make impression on it. It is thickest thickest upon the base, and gradually, as the roots turn smaller, becomes thinner. — The fibres of this enamel are all perpendicular to the internal substance, and are straight on the base, but at the sides are arched with a convex part towards the roots; which makes the teeth resist the compression of any hard body between the jaws, with less danger of breaking these fibres, than if they had been situated transversely. The spongy sockets in which the teeth are placed likewise serve better to prevent such an injury, than a more solid base would have done.

The bony part of the teeth has its fibres running straight, according to the length of the teeth. When it is exposed to the air, by the breaking or falling off of the hard cortex, it soon corrupts. And hence carious teeth are often all hollow within, when a very small hole appears only externally.

The teeth have canals formed in their middle, wherein their nerves and blood-vessels are lodged; which they certainly need, being constantly waited by the attrition they are subjected to in mastication, and for their further growth, not only after they first appear, but even in adults; as is evident when a tooth is taken out: For then the opposite one becomes longer, and those on each side of the empty socket turn broader; so that when the jaws are brought together, it is scarce observable where the tooth is wanting.

The vessels are easily traced so long as they are in the large canal, but can scarcely be observed in their distribution from that to the substance of the teeth of adults. — This plentiful supply of vessels must expose the teeth to the same disorders that attack other vascular parts.

Every root of each tooth has such a distinct canal, with vessels and nerves in it. These canals in the teeth with more than one root, come nearer each other, as they approach the base of the tooth; and at last are only separated by very thin plates, which being generally incomplete, allow a communication of all the canals; and frequently one common cavity only appears within the base, in which a pulpy substance, composed of nerves and vessels, is lodged.

The entry of the canals for these vessels is a small hole placed a little to a side of the extreme point of each root; sometimes, especially in old people, this hole is entirely closed up, and consequently the nerves and blood-vessels are destroyed.

The teeth are seen for a considerable time in form of mucus contained in a membrane; afterwards a thin cortical plate, and some few osseous layers appear within the membrane, with a large cavity filled with mucus in the middle; and gradually this exterior shell turns thicker, the cavity decreases, the quantity of mucus is lessened, and this induration proceeds till all the body is formed; from which the roots are afterwards produced.

In young subjects, different flamina, or rudiments of teeth, are to be observed. Those next the gums hinder ordinarily the deeper-seated ones from making their way out, while these prevent the former from sending out roots, or from entering deep into the bony sockets of the jaws; by which they come to be less fixed.

Children are seldom born with teeth; but at two years of age they have twenty; and their number does not increase till they are about seven years old, when the teeth that first made their way through the gums are thrust out by others that have been formed deeper in the jaw, and some more of the teeth begin to discover themselves farther back in the mouth. About fourteen years of age, some more of the first crop are shed, and the number is increased. — This shedding of the teeth is of good use; for if the first had remained, they would have stood at a great distance one from another; because the teeth are too hard in their outer crust, to increase so fast as the jaws do. Whereas both the second layer, and the teeth that come out late, meeting, while they are soft, with a considerable resistance to their growth in length, from those situated upon them, necessarily come out broad, and fit to make that close guard to the mouth, which they now form.

The teeth are joined to the sockets by gomphosis, and the gums contribute to fix them there; as is evident by the teeth falling out when the gums are any way destroyed, or made too spongy; as in the scurvy or salivations: Whence some call this articulation with the syphilis.

The uses of the teeth are to masticate our aliment, and to assist us in the pronunciation of several letters.

Though the teeth so far agree in their structure, yet, because of some things wherein they differ, they are generally divided into three classes, viz. incisors, canines, and molars.

The incisors, are the four fore-teeth in each jaw, receiving their name from their office of cutting our aliment; for which they are excellently adapted, being each formed into a sharp-cutting edge at their base, by their fore-side turning inwards there, while they are slopped down and hollowed behind; so that they have the form of wedges; and therefore their power of acting must be considerably increased.

The incisors of the upper jaw, especially the two middle ones, are broader and longer generally than those of the under jaw.

Canines, from the resemblance to dogs tusks, are one on each side of the incisors in each jaw. — The two in the upper jaw are called eye-teeth, from the communication of nerves which is said to be betwixt them and the eyes. — The two in the lower jaw are named angular, or mike-teeth, because they support the angles of the mouth.

The canines are broader, longer, and stronger, than the incisors. — Their bases are formed into a sharp edge, as the incisors are; only that the edge rises into a point in the middle. — Each of them has generally but one long root, though sometimes they have two. The roots are crooked towards the end. — The canines of the upper jaw are larger, longer, and with more crooked roots, than those of the under jaw.

The dentes molares, or grinders, which have got their name because they grind our food, are generally five in each side of each jaw; in all twenty. Their bases are broader, more scabrous, and with a thinner cortical substance, than the other teeth. They have also more roots, roots, and as these roots generally divericate from each other, the partitions of the sockets between them bear a large share of the great pressure they suffer, and hinder it to act on their points.

The numerous roots of the dentic molares prevent their loosening by the lateral pressure they suffer in grinding; and as the sockets in the upper jaw are more spongy, and the teeth are more liable, by their situation, to fall out, the grinders there have more numerous and more separated roots than in the lower jaw.

According to the division made of the skeleton, we should now proceed to the description of the trunk of the body. But must first consider a bone, which cannot well be said to belong to either the head or the trunk; nor is it immediately joined to any other, and therefore is very seldom preferred with skeletons.

The Os Hyoides, which is situated horizontally between the root of the tongue and the larynx. It is properly enough named hyoides, from the resemblance it bears to the Greek letter v, and may, for a clearer demonstration of its structure, be distinguished into its body, cornua, and appendices.

The body is the middle broad part, convex before, and hollow behind.—The convex fore-part is divided into two, by a ridge, into the middle of which the mylo-hyoidei, and into the sides the stylo-hyoidei, muscles are inserted.—Above the ridge, the bone is horizontal, but pitted in the middle by the insertion of the two genio-hyoidei muscles, and a little hollowed more laterally by the basihyoidi.—Below the ridge, it is convex, but a little flatted in the middle by the sterno-hyoidei, and pitted more externally by the coraco-hyoidei.—The concavity behind faces backwards and downwards to receive the thyroid cartilage, when the larynx and the os hyoides are pulled towards each other by the action of the sterno-hyoidei and hyothyroidei muscles; and to its upper edge, the ligamentous membranes of the epiglottis, tongue, and thyroid cartilage, are fixed.

The cornua of the os hyoides are stretched backwards from each side of its body, where often a small furrow points out the former separation.—These cornua are not always straight, nor of equal length; their two plain surfaces stand obliquely slopping from above, outwards and downwards.—Into the external, the cerato glossus is inserted above, and the thyro-hyoideus muscle below; and to the one behind, the ligamentous membrane of the tongue and larynx adheres. Each of the cornua becomes gradually smaller, as it is extended from the base; but ends in a round tubercle, from which a movable cartilage stands out, which is connected to the upper process of the cartilago thyroidea.

Where the body of the os hyoides joins on each side with its cornua, a small styiform process, called appendix, rises upwards and backwards, into which the musculi stylo-hyoidei alteri, and part of the hyo-glossi muscles are fixed.

The substance of the os hyoides is cellular, but covered with a firm external plate, which is of sufficient strength to bear the actions of so many muscles as are inserted into it.

It is not articulated with any bone of the body, except by means of the muscles and ligaments mentioned.

The use of the os hyoides, is to serve as a solid lever for the muscles to act with, in raising or depressing the tongue and larynx, or in enlarging and diminishing the capacity of the fauces.

OF THE TRUNK.

The Trunk consists of the spine, pelvis, and thorax.

The Spine is the long pile of bones extended from the condyles of the occiput to the end of the rump. It somewhat resembles two unequal pyramids joined in a common base. It is not, however, straight; for its upper part being drawn backwards by strong muscles, it gradually advances forwards, to support the oesophagus, vessels of the head, &c. Then it turns backwards, to make place enough for the heart and lungs. It is next bended forwards, to support the viscera of the abdomen. It afterwards turns backwards, for the enlargement of the pelvis. And, lastly, it is reflected forwards, for sustaining the lowest great gut.

The spine is commonly divided into true and false vertebrae; the former constituting the long upper pyramid, which has its base base below, while the false vertebra make the shorter lower pyramid, whose base is above.

The True Vertebrae are the twenty-four upper bones of the spine, on which the several motions of the trunk of our bodies are performed; from which use they have justly got their name.

Each of these vertebrae is composed of its body and processes.

The body is the thick spongy fore-part, which is convex before, concave backwards, horizontal and plain in most of them above and below.—Numerous small holes, especially on the fore and back-part of their surface, give passage to their vessels, and allow the ligaments to enter their substance.—The edges of the body of each vertebra are covered, especially at the fore-part, with a ring of bone firmer and more solid than the substance of the body anywhere else. These rings are of great use in preventing the spongy bodies from being broken in the motions of the trunk.

Between the bodies of each two adjoining vertebra, a substance between the nature of ligament and cartilage is interposed; which seems to consist of concentrical curve fibres, when it is cut horizontally; but when it is divided perpendicularly, the fibres appear oblique and decussating each other.—The outer part of the intervertebral ligaments is the most solid and hard; and they gradually become softer till they are almost in the form of a glairy liquor in the centre; and therefore these substances were not improperly called mucous ligaments by the ancients. The external fibrous part of each is capable of being greatly extended, and of being compressed into a very small space, whilst the middle fluid part is incompressible, or nearly so; and the parts of this ligament between the circumference and centre approach in their properties to either, in proportion to their more solid or or more fluid texture. The middle point is therefore a fulcrum or pivot, on which the motion of a ball and socket may be made, with such a gradual yielding of the substance of the ligament, in whichever direction our spines are moved, as saves the body from violent shocks, and their dangerous consequences.—This ligamento-cartilaginous substance is firmly fixed to the horizontal surfaces of the bodies of the vertebrae, to connect them, in which it is assisted by a strong membranous ligament, which lines all their concave surface, and by still a stronger ligament, that covers all their anterior convex surface.

From each side of the body of each vertebra, a bony bridge is produced backwards, and to a side; from the posterior end of which, one flanking process rises and another descends; the smooth, and what is generally the flattest side of each of these four processes, which are called the oblique, is covered with a smooth cartilage; and the two lower ones of each vertebra, are fitted to, and articulated with the two upper or ascending oblique processes of the vertebra below, having their articular ligaments fixed into the rough line round their edges.

From between the oblique processes of each side the vertebra is stretched out laterally into a process that is named transverse.

From the back-part of the roots of the two oblique, and of the transverse process of each side, a broad oblique bony plate is extended backwards, where these meet, the seventh process of the vertebra takes its rise, and stands out backwards: This being generally sharply pointed, and narrow edged, has therefore been called spinal process; from which this whole chain of bones has got its name.

Besides the common ligament which lines all the internal surface of the spinal processes, as well as of the bodies, there are particular ligaments that connect the bony bridges and processes of the contiguous vertebrae together.

The substance of the processes is considerably stronger and firmer, and has a thicker external plate than the bodies of the vertebrae have.

The seven processes form a concavity at their fore-part, which, joined to the one at the back-part of the bodies, makes a great hole, and the holes of all the vertebrae form a long large conduit, for containing the spinal marrow.—In the upper and lower edge of each lateral bridge, there is a notch. These are so adapted to each other in the contiguous vertebrae, as to form a round hole in each side between each two vertebrae, through which the nerves that proceed from the spinal marrow and its blood-vessels pass.

The articulations then of these true vertebrae are plainly double; for their bodies are joined by the intervening cartilage above described, and their oblique processes being tipped with cartilages, are so connected by their ligaments, as to allow a small degree of motion to all sides.

The true vertebrae serve to give us an erect posture; to allow sufficient and secure motion to the head, neck, and trunk of the body, and to support and defend the bowels, and other soft parts.

Though the true vertebrae agree in the general structure which we have hitherto described; yet because of several specialities proper to a particular number, they are commonly divided into three classes, viz. cervical, dorsal, and lumbar.

The cervical are the seven uppermost vertebrae; which are distinguished from the rest by these marks.—Their bodies are smaller and more solid than any others, and flattened on the fore-part, to make way for the oesophagus; or rather this flat figure is owing to the pressure of that pipe, and to the action of the longi colli and anterior recti muscles.—They are also flat behind, where small processes rise, to which the internal ligaments are fixed.—The upper surface of the body of each vertebra is made hollow, by a flanking thin process which is raised on each side.—The lower surface is also excavated, but in a different manner; for here the posterior edge is raised a little, and the one before is produced a considerable way.—Hence we see how the cartilages between those bones are firmly connected, and their articulations are secure.

The cartilages between these vertebrae are thick, especially at their fore-part; which is one reason why the vertebrae advance forward as they descend, and have larger motion.

The oblique processes of these bones of the neck more justly deserve that name than those of any other vertebra. They are situated flanking; the upper ones having their smooth and almost flat surfaces facing obliquely backwards and upwards, while the inferior oblique processes have their surfaces facing obliquely forwards and downwards.

The transverse processes of these vertebrae are framed in a different manner from those of any other bones of the spine: For besides the common transverse process rising from between the oblique processes of each side, there is a second one that comes out from the side of the body of each vertebra; and these two processes, after leaving a circular hole for the passage of the cervical artery and vein, unite, and are considerably hollowed at their upper part, with rising sides, to protect the nerves that pass in the hollow; and at last each side terminates in an obtuse point, for the insertion of muscles.

The spinal processes of these cervical bones stand nearly straight backwards, are shorter than those of any other vertebra, and are forked or double at their ends; and hence allow a more convenient insertion to muscles.

So far most of the cervical vertebra agree; but they have some particular differences, which oblige us to consider them separately.

The first, from its use of supporting the head, has the name of atlas; and is also called epistrophoea, from the motion it performs on the second.

The atlas, contrary to all the other vertebrae of the spine, has no body; but, instead of it, there is a bony arch.—In the convex fore-part of which, a small rising appears, where the musculi longi colli are inserted; and, on each side of this protuberance, a small cavity may be observed, where the recti interni minores take their rise.—The upper and lower parts of the arch are rough and unequal, where the ligaments that connect connect this vertebra to the os occipitis, and to the second vertebra, are fixed.—The back-part of the arch is concave, smooth, and covered with a cartilage, in a recent subject, to receive the tooth-like process of the second vertebra.—In a first vertebra, from which the second has been separated, this hollow makes the passage for the spinal marrow to seem much larger than it really is: On each side of it a small rough sinuosity may be remarked, where the ligaments going to the sides of the tooth-like process of the following vertebra are fastened; and on each side, a small rough protuberance and depression is observable, where the transverse ligament, which secures the tooth-like process in the sinuosity, is fixed, and hinders that process from injuring the medulla spinalis in the flexions of the head.

The atlas has as little spinal process as body; but instead thereof, there is a large bony arch, that the muscles which pass over this vertebra at that place might not be hurt in extending the head.

The superior oblique processes of this atlas are large, oblong, hollow, and more horizontal than in any other vertebra.—They rise more in their external than internal brim; by which their articulations with the condyloid of the os occipitis are firmer.—Under the external edge of each of these oblique processes, is the fossa, or deep open channel, in which the vertebral arteries make the circular turn, as they are about to enter the great foramen of the occipital bone, and where the tenth pair of nerves goes out.—The inferior oblique processes extending from within outwards and downwards, are large, concave, and circular. So that this vertebra, contrary to the other six, receives the bones with which it is articulated both above and below.

The transverse processes here are not much hollowed or forked, but are longer and larger than those of any other vertebra of the neck, for the origin and insertion of several muscles.

The hole for the spinal marrow is larger in this than in any other vertebra, not only on account of the marrow being largest here, but also to prevent its being hurt by the motions of this vertebra on the second one.—This large hole, and the long transverse processes, make this the broadest vertebra of the neck.

The condyles of the os occipitis move forwards and backwards in the superior oblique processes of this vertebra; but from the figure of the bones forming these joints, it appears, that very little motion can here be allowed to either side; and there must be still less circular motion.

The second vertebra colli is called dentata, from the tooth-like process on the upper part of its body.

The body of this vertebra is somewhat pyramidal, being large, and produced downwards, especially at its fore-side, to enter into a hollow of the vertebra below; while the upper part has a square process with a small point standing out from it. This it is that is imagined to resemble a tooth, and has given name to the vertebra.—The side of this process, on which the hollow of the anterior arch of the first vertebra plays, is convex, smooth, and covered with a cartilage; and it is of the same form behind, for the ligament, which is extended transversely from one rough protuberance of the first vertebra to the other, and is cartilaginous in the middle, to move on it.

The superior oblique processes of this vertebra dentata are large, circular, very nearly in an horizontal position, and slightly convex, to be adapted to the inferior oblique processes of the first vertebra.

The transverse processes of the vertebra dentata are short, very little hollowed at their upper part, and not forked at their ends; and the canals through which the cervical arteries pass, are reflected outwards about the middle substance of each process; so that the course of these vessels may be directed towards the transverse processes of the first vertebra.

The spinal process of this vertebra dentata is thick, strong, and short, to give sufficient origin to the musculi recti majores, and obliqui inferiores, and to prevent the contusion of these and other muscles in pulling the head back.

The third vertebra of the neck is by some called axis; but this name is applied to it with much less reason than to the second.—This third, and the three below, have nothing particular in their structure; but all their parts come under the general description formerly given, each of them being larger as they descend.

The seventh vertebra of the neck is near to the form of those of the back, having the upper and lower surfaces of its body less hollow than the others.—The oblique processes are more perpendicular;—neither spinal nor transverse processes are forked.—This seventh and the sixth vertebrae of the neck have the hole in each of their transverse processes, more frequently divided by a small cross bridge, that goes between the cervical vein and artery, than any of the other vertebrae.

The twelve dorsal may be distinguished from the other vertebrae of the spine by the following marks.

Their bodies are of a middle size, betwixt those of the neck and loins;—they are more convex before than either of the other two sorts; and are flatted laterally by the pressure of the ribs, which are inserted into small cavities formed in their sides. This flating on their sides, which makes the figure of these vertebrae almost an half oval, is of good use; as it affords a firm articulation to the ribs, allows the trachea arteria to divide at a small angle, and the other large vessels to run secure from the action of the vital organs.—These bodies are more concave behind than any of the other two classes.—Their upper and lower surfaces are horizontal.

The cartilages interposed between the bodies of these vertebrae are thinner than in any other of the true vertebrae; and contribute to the concavity of the spine in the thorax, by being thinnest at their fore-part.

The oblique processes are placed almost perpendicular; the upper ones flanging but a little forwards, and the lower ones flanging as much backwards.—They have not as much convexity or concavity as is worth remarking.—Between the oblique processes of opposite sides, several sharp processes stand out from the upper and lower parts of the plates which join to form the spinal process; into these sharp processes strong ligaments are fixed, for connecting the vertebrae. The transverse processes of the dorsal vertebrae are long, thicker at their ends than in the middle, and turned obliquely backwards.

The spinal processes are long, small pointed, and sloping downwards and backwards; from their upper and back-part a ridge rises, which is received by a small channel in the fore-part of the spinal process immediately above, which is here connected to it by a ligament.

The conduit of the spinal marrow is here more circular, but, corresponding to the size of that cord, is smaller than in any of the other vertebrae, and a larger share of the holes in the bony bridges, for the transmission of the nerves, is formed in the vertebra above, than in the one below.

The connection of the dorsal vertebrae to the ribs, the thinness of their cartilages, the erect situation of the oblique processes, the length, sloping, and connection of the spinal processes, all contribute to restrain these vertebrae from much motion, which might disturb the actions of the heart and lungs; and, in consequence of the little motion allowed here, the intervertebral cartilages sooner shrivel, by becoming more solid: And therefore, the first remarkable curvature of the spine observed, as people advance to old age, is in the least stretched vertebrae of the back; or old people first become round-shouldered.

The bodies of the four uppermost dorsal vertebrae deviate from the rule of the vertebrae, becoming larger as they descend; for the first of the four is the largest, and the other three below gradually become smaller, to allow the trachea and large vessels to divide at smaller angles.

The two uppermost vertebrae of the back, instead of being very prominent forwards, are flattened by the action of the musculi longi colli and recti majores.

The proportional size of the two little depressions in the body of each vertebra, for receiving the heads of the ribs, seems to vary in the following manner; the depression on the upper edge of each vertebra decreases as far down as the fourth, and after that increases.

The transverse processes are longer in each lower vertebra to the seventh or eighth, with their smooth surfaces, for the tubercles of the ribs, facing gradually more downwards; but afterwards, as they descend, they become shorter, and the smooth surfaces are directed more upwards.

The spinous processes of the vertebrae of the back become gradually longer and more slanting from the first, as far down as the eighth or ninth vertebra; from which they manifestly turn shorter and more erect.

The first vertebra, besides an oblong hollow in its lower edge, that assists in forming the cavity wherein the second rib is received, has the whole cavity for the head of the first rib formed in it.

The second has the name of axillary, without anything particular in its structure.

The eleventh often has the whole cavity for the eleventh rib in its body, and wants the smooth surface on each transverse process.

The twelfth always receives the whole head of the last rib, and has no smooth surface on its transverse processes, which are very short.—The smooth surfaces of its inferior oblique processes face outwards as the lumbar do.

And we may say in general, that the upper vertebrae of the back lose gradually their resemblance to those of the neck, and the lower ones come nearer to the figure of the lumbar.

The lowest order of the true vertebrae is the lumbar, which are five bones, that may be distinguished from any others by these marks: 1. Their bodies, though of a circular form at their fore-part, are somewhat oblong from one side to the other; which may be occasioned by the pressure of the large vessels, the aorta and cava, and of the viscera. The epiphyses on their edges are larger, and therefore the upper and lower surfaces of their bodies are more concave than in the vertebrae of the back.

2. The cartilages between these vertebrae are much the thickest of any, and render the spine convex within the abdomen, by their greatest thickness being at their fore-part.

3. The oblique processes are strong and deep; those in opposite sides being almost placed in parallel planes; the superior, which are concave, facing inwards, and the convex inferior ones facing outwards; and therefore each of these vertebrae receives the one above it, and is received by the one below; which is not so evident in the other two classes already described.

4. Their transverse processes are small, long, and almost erect, for allowing large motion to each bone, and sufficient insertion to muscles, and for supporting and defending the internal parts.

5. Betwixt the roots of the superior oblique and transverse processes, a small protuberance may be observed, where some of the muscles that raise the trunk of the body are inserted.

6. Their spinal processes are strong, straight, and horizontal, with broad flat sides, and a narrow edge above and below; this last being depressed on each side by muscles. And at the root of these edges, we see rough surfaces for fixing the ligaments.

7. The canal for the numerous cords, called cauda equina, into which the spinal marrow divides, is rather larger in these bones than what contains that marrow in the vertebrae of the back.

8. The holes for the passage of the nerves are more equally formed out of both the contiguous vertebrae than in the other classes; the upper one furnishes however the larger share of each hole.

The thick cartilages between these lumbar vertebrae, their deep oblique processes, and their erect spinal processes, are all fit for allowing large motion; though it is not so great as what is performed in the neck; which appears from comparing the arches which the head describes when moving on the neck, or the loins only.

The lumbar vertebrae, as they descend, have their oblique processes at a greater distance from each other, and facing more backwards and forwards.

Both transverse and spinal processes of the middlemost vertebrae of the loins are longest and thickest; in the vertebra above and below they are less; so that these processes of the first and fifth are the least, to prevent their striking on the ribs or os ilium, or their bruising the muscles in the motions of the spine.

The epiphyses round the edges of the bodies of the lumbar vertebrae are most raised in the two lowest, which consequently make them appear hollower in the middle than the others are. The body of the fifth vertebra is rather thinner than that of the fourth.—The spinal process of this fifth is smaller, and the oblique processes face more backwards and forwards than in any other lumbar vertebra.

The False Vertebrae compose the under pyramid of the spine. They are distinguished from the bones already described justly enough by this epithet of false; because, though each bone into which they can be divided in young people, resembles the true vertebrae in figure, yet none of them contribute to the motion of the trunk of the body; they being intimately united to each other in adults, except at their lower part, where they are moveable; whence they are commonly divided into two bones, os sacrum and coccygis.

Os Sacrum, is so called from being offered in sacrifice by the ancients, is of an irregular triangular shape, broad above, narrow below, convex behind, for the advantageous origin of the muscles that move the spine and thigh backwards; and concave behind, for enlarging the cavity of the pelvis.—Four transverse lines of a colour different from the rest of the bone, which are seen on its fore-part, are the marks of division of the five different bones of which it consists in young persons.

The fore-part of the os sacrum is smooth and flat, to allow a larger space for the contained bowels, without any danger of hurting them.—The back-part of it is almost straight, without a large cavity as the vertebrae have.—The bridges between the bodies and processes of this bone, are much thicker, and in proportion shorter, than in the former clasps of bones.—The strength of these cross-bridges is very remarkable in the three upper bones, and is well-proportioned to the incumbent weight of the trunk of the body, which these bridges sustain in a transverse, consequently an unfavourable, situation, when the body is erect.

There are only two oblique processes of the os sacrum; one standing out on each side from the upper part of the first bone.—Their plain erect surfaces face backwards, and are articulated with the inferior oblique processes of the last vertebra of the loins, to which each of these processes is connected by a strong ligament, which rises from a scabrous cavity round their roots, where mucilaginous glands are also lodged.—Instead of the other oblique processes of this bone, four rough tubercles are to be seen on each side of its surface behind, from which the nucleus sacri has its origin.

The transverse processes here are all grown together into one large strong oblong process on each side; which, so far as it answers to the first three bones, is very thick, and divided into two irregular cavities, by a long perpendicular ridge.—The foremost of the two cavities has commonly a thin cartilaginous skin covering it in the recent subject, and is adapted to the unequal protuberance of the os ilium, and a strong ligament connects the circumference of these surfaces of the two bones.—The cavity behind is divided by a transverse ridge into two, where strong ligamentous strings that go from this bone to the os ilium, with a cellular substance containing mucus, are lodged.

The transverse processes of the two last bones of the os sacrum are much smaller than the former.—At their back-part, near their edge, a knob and oblong flat surface give rise to two strong ligaments which are extended to the os ilium; and are therefore called sacroiliac.

The spinal processes of the three uppermost bones of the os sacrum appear short, sharp, and almost erect, while the two lower ones are open behind; and sometimes a little knob is to be seen on the fourth, though generally it is bifurcated, without the two legs meeting into a spine; in which condition also the first is often to be seen. The musculus latissimus, and longissimus dorsi, sacrolumbalis, and gluteus maximus, have part of their origins from these spinal processes.

The canal between the bodies and processes of this bone, for the cauda equina, is triangular; and becomes smaller as it descends, as the cauda also does.—Below the third bone, this passage is no more a complete bony canal, but is open behind; and is only there defended by a strong ligamentous membrane stretched over it, which, with the muscles that cover it, and are very prominent on each side, is a sufficient defence for the bundle of nerves within.

At the root of each oblique process of this bone, the notch is conspicuous, by which, and such another in the last vertebra of the loins, a passage is left for the twenty-fourth spinal nerve; and, in viewing the os sacrum, either before or behind, four large holes appear in each side, in much the same height, as where the marks of the union of its several bones remain. Some of the largest nerves of the body pass through the anterior holes; and superficial grooves running outwards from them in different directions, show the course of these nerves.—From the intervals of these grooves, the pyriformis muscle chiefly rises.—The holes in the back-part of the bone are covered by membranes which allow small nerves to pass through them.—The two uppermost of these holes, especially on the fore-side, are the largest; and as the bone descends, the holes turn smaller. Sometimes a notch is only formed at the lower part in each side of this bone; and in other subjects there is a hole common to it and the os coccygis, through which the twenty-ninth pair of spinal nerves passes; and frequently a bony bridge is formed on the back-part of each side by a process sent up from the back-part of the os coccygis, and joined to the little knobs which the last bone of the os sacrum has instead of a spinal process. Under this bridge or jugum, the twenty-ninth pair of spinal nerves runs in its course to the common holes just now described.

The substance of the os sacrum is very spongy, without any considerable solid external plates, and is lighter proportionally to its bulk than any other bone in the body; but is secured from injuries by the thick muscles that cover it behind, and by the strong ligamentous membranes that closely adhere to it.

This bone is articulated above to the last vertebra of the loins, in the manner that the lumbar vertebrae are joined; and therefore the same motions may be performed here.—The articulation of the lower part of the os sacrum to the os coccygis seems well enough adapted for allowing allowing considerable motion to this last bone, was it not much confined by ligaments. Laterally, the os sacrum is joined to the osa ilium by an immovable synchondrosis.

The uses of the os sacrum are, to serve as the common base and support of the trunk of the body, to guard the nerves proceeding from the end of the spinal marrow, to defend the back-part of the pelvis, and to afford sufficient origin to the muscles which move the trunk and thighs.

Os Coccygis, or rump-bone, is that triangular chain of bones depending from the os sacrum; each bone becoming smaller as they descend, till the last ends almost in a point. The os coccygis is convex behind, and concave before; from which crooked pyramidal figure, which was thought to resemble a cuckow's beak, it has got its name.

This bone consists of four pieces in people of middle age:—In children, very near the whole of it is cartilage: In old subjects, all the bones are united, and become frequently one continued bone with the os sacrum.

The highest of the four bones is the largest, with shoulders extended farther to each side than the end of the os sacrum;—the upper surface of this bone is a little hollow.—From the back of that bulbous part called its shoulders, a process often rises up on each side, to join with the bifurcated spine of the fourth and fifth bones of the os sacrum, to form the bony bridge mentioned in the description of the os sacrum.—Immediately below the shoulders of the os coccygis, a notch may be remarked in each side, where the thirtieth pair of the spinal nerves passes.—The lower end of this bone is formed into a small head, which very often is hollow in the middle.

The three lower bones gradually become smaller, and are spongy; but are strengthened by a strong ligament which covers and connects them.—Their ends, by which they are articulated, are formed in the same manner as those of the first bone are.

The lower end of the fourth bone terminates in a rough point, to which a cartilage is appended.

To the sides of these cones of the os coccygis, the coccygei muscles, and part of the levatores ani, and of the glutei maximi, are fixed.

The os coccygis serves to sustain the intestinum rectum; and, in order to perform this office more effectually, it is made to turn with a curve forwards; by which also the bone itself, as well as the muscles and teguments, is preserved from any injury, when we sit with our body reclined back.

The second part of the trunk of the skeleton, the Pelvis, is the cylindrical cavity at the lower part of the abdomen, formed by the os sacrum, os coccygis, and osa innominata; which last therefore fall now in course to be examined.

The Ossa Innominata are two large broad bones, which form the fore-part and sides of the pelvis, and the lower part of the sides of the abdomen.—In children each of these bones is evidently divided into three; which are afterwards so intimately united, that scarce the least mark of their former separation remains: notwithstanding, they are described as consisting each of three bones, to wit, the os ilium, ischium, and pubis.

Os Ilium, or haunch-bone, is situated highest of the three, and reaches as far down as one third of the great cavity into which the head of the thigh-bone is received.

The external side of this bone is unequally convex, and is called its dorsum;—the internal concave surface is by some (but improperly) named coxa.—The semicircular edge at the highest part of this bone, which is tipped with a cartilage in the recent subject, is named the spine, into which the external or descending oblique muscle of the abdomen is inserted; and from it the internal ascending oblique and the transverse muscles of the belly, with the gluteus maximus, quadratus lumborum, and latissimus dorsi, have their origin.—The ends of the spine are more prominent than the surface of the bone below them; therefore are reckoned processes.—From the anterior spinal process, the sartorius and fascialis muscles have their rise, and the outer end of the doubled tendon of the external oblique muscle of the abdomen, commonly called Fallopian's or Poupart's ligament, is fixed to it.—The inside of the posterior spinal process, and of part of the spine forward from that, is made flat and rough where the sacro-lumbalis and longissimus dorsi rise; and to its outside ligaments, extended to the os sacrum and transverse processes of the fifth and fourth vertebrae of the loins, are fixed.—Below the anterior spinal process another protuberance stands out, which, by its situation, may be distinguished from the former, by adding the epithet of inferior, where the musculus rectus tibiae has its origin.—Betwixt these two anterior processes the bone is hollowed where the beginning of the sartorius muscle is lodged.—Below the posterior spinal processes, a second protuberance of the edge of this bone is in like manner observable, which is closely applied to the os sacrum.—Under this last process a considerable large niche is observable in the os ilium; between the sides of which and the strong ligament that is stretched over from the os sacrum to the sharp-pointed process of the os ischium of the recent subject, a large hole is formed, through which the musculus pyriformis, the great sciatic nerve, and the posterior crural vessels, pass, and are protected from compression.

The external broad side, or dorsum of the os ilium, is a little hollow towards the fore part; farther back it is as much raised; then is considerably concave; and, lastly, it is convex. These inequalities are occasioned by the actions of the muscles that are situated on this surface.—From behind the uppermost of the two anterior spinal processes, in such bones as are strongly marked by the muscles, a semicircular ridge is extended to the hollow passage of the sciatic nerve. Between the spine and this ridge, the gluteus medius takes its rise. Immediately from above the lowest of the anterior spinal processes, a second ridge is stretched to the niche. Between this and the former ridge, the gluteus minimus has its origin.—On the outside of the posterior spinal processes, the dorsum of the os ilium is flat and rough, where part of the musculus gluteus maximus and pyriformis rises.—The lowest part of this bone is the thickest, and is formed into a large large cavity with high brims, to assist in composing the great acetabulum.

The internal surface of the os ilium is concave in its broadest fore part, where the internal iliac muscle has its origin, and some share of the intestinum ilium and colon is lodged.—From this large hollow, a small sinuosity is continued obliquely forwards, at the inside of the anterior inferior spinal process, where part of the psoas and iliacus muscles, with the crural vessels and nerves, pass.—The large concavity is bounded below by a sharp ridge, which runs from behind forwards, and, being continued with such another ridge of the os pubis, forms a line of partition between the abdomen and pelvis.—Into this ridge the broad tendon of the psoas parvus is inserted.

All the internal surface of the os ilium, behind this ridge, is very unequal: For the upper part is flat, but spongy, where the sacro-lumbalis and longissimus dorsi rise.—Lower down, there is a transverse ridge from which ligaments go out to the os sacrum.—Immediately below this ridge, the rough unequal cavities and prominences are placed, which are exactly adapted to those described on the side of the os sacrum.—In the same manner, the upper part of this rough surface is porous, for the firmer adhesion of the ligamentous cellular substance; while the lower part is more solid, and covered with a thin cartilaginous skin, for its immoveable articulation with the os sacrum.

Os Ischium, or hip-bone, is of a middle bulk between the two other parts of the os innominatum, is situated lowest of the three, and is of a very irregular figure.—Its extent might be marked by an horizontal line drawn near through the middle of the acetabulum; for the upper bulbous part of this bone forms some less than the lower half of that great cavity, and the small leg of it rises to much the same height on the other side of the great hole common to this bone and the os pubis.

From the upper thick part of the os ischium, a sharp process, called by some spinous, stands out backwards, from which chiefly the musculus coccygeus and superior gemellus, and part of the levator ani, rise; and the anterior or internal sacrofascial ligament is fixed to it.—Immediately below this process, a sinuosity is formed for the tendon of the musculus obturator internus.—In a recent subject, this part of the bone, which serves as a pulley on which the obturator muscle plays, is covered with a ligamentous cartilage, that, by two or three small ridges, points out the intertices of the fibres in the tendon of this muscle.—The outer surface of the bone at the root of this spinous process is made hollow by the pyriformis, or iliacus externus muscle.

Below the sinuosity for the obturator muscle, is the great knob or tuberosity, covered with cartilage or tendon.—The upper part of the tuberosity gives rise to the inferior gemellus muscle.—To a ridge at the inside of this, the external or posterior sacrofascial ligament is so fixed, that between it, the internal ligament, and the sinuosity of the os ischium, a passage is left for the internal obturator muscle.—The upper thick smooth part of the tuber, called by some its dorsum, has two oblique impressions on it. The inner one gives origin to the long head of the biceps flexor tibise and seminervosus muscles, and the femoromembranosus rises from the exterior one, which reaches higher and nearer the acetabulum than the other.—The lower, thinner, more scabrous part of the knob which bends forwards, is also marked with two flat surfaces, whereof the internal is what we lean upon in sitting, and the external gives rise to the largest head of the triceps adductor femoris.—Between the external margin of the tuberosity, and the great hole of the os innominatum, there is frequently an obtuse ridge extended down from the acetabulum, which gives origin to the quadratus femoris.—As the tuber advances forwards, it becomes smaller, and is rough, for the origin of the musculus transversalis and erector penis.—The small leg of it, which mounts upwards to join the os pubis, is rough and prominent at its edge, where the two lower heads of the triceps or quadriceps adductor femoris take their rise.

The upper and back part of the os ischium is broad and thick; but its lower and fore-part is narrower and thinner.

The os ilium and pubis of the same side are the only bones which are contiguous to the os ischium.

The Os Pubis, or share-bone, is the least of the three parts of the os innominatum, and is placed at the upper fore-part of it.—The thick largest part of this bone is employed in forming the acetabulum; from which, becoming much smaller, it is stretched inwards to its fellow of the other side, where again it grows larger, and sends a small branch downwards to join the end of the small leg of the os ischium.—The upper fore-part of each os pubis is tuberous and rough where the musculus rectus and pyramidalis are inserted.—From this a ridge is extended along the upper edge of the bone, in a continued line with such another of the os ilium, which divides the abdomen and pelvis. The ligament of Fallopia is fixed to the internal end of this ridge, and the smooth hollow below it is made by the psoas and iliacus internus muscles passing with the anterior crural vessels and nerves behind the ligament.—Some way below the former ridge, another is extended from the tuberous part of the os pubis downwards, and onwards towards the acetabulum; between these two ridges the bone is hollow and smooth, for lodging the head of the pecineus muscle.—Immediately below, where the lower ridge is to take the turn downwards, a winding notch is made, which is comprehended in the great foramen of a skeleton, but is formed into a hole by a subcended ligament in the recent subject, for the passage of the posterior crural nerve, an artery, and a vein.—The internal end of the os pubis is rough and unequal, for the firmer adhesion of the thick ligamentous cartilage that connects it to its fellow of the other side:—The process which goes down from that to the os ischium is broad and rough before, where the gracilis and upper heads of the triceps, or rather quadriceps adductor femoris, have their origin.

Betwixt the os ischium and pubis a very large irregular hole is left, which, from its resemblance to a door or shield, has been called thyroides. This hole is all, except the notch for the posterior crural nerve, filled up, in a recent subject, with a strong ligamentous membrane, that adheres very firmly to its circumference. From this membrane chiefly the two obturator muscles, external and internal, take their rise.—The great design of this hole, besides rendering the bone lighter, is to allow a strong enough origin to the obturator muscles, and sufficient space for lodging their bellies, that there may be no danger of disturbing the functions of the contained viscera of the pelvis by the actions of the internal, nor of the external being bruised by the thigh-bone, especially by its lesser trochanter, in the motions of the thigh inwards.—The bowels sometimes make their way through the notch for the vessels, at the upper part of this thyroid hole, which causes a hernia in this place.

In the external surface of the os innominatum, near the outside of the great hole, a large deep cavity is formed by all the three bones conjunctly: For the os pubis constitutes about one fifth; the os ilium makes something less than two fifths, and the os ischium as much more than two fifths. The brims of this cavity are very high, and are still much more enlarged by the ligamentous cartilage, with which they are tipped in a recent subject. From this form of the cavity it has been called acetabulum; and, for a distinguishing character, the name of the bone that contributes the largest share of it is added; therefore acetabulum ossis ischii is the name this cavity commonly bears.—Round the base of the supercilia the bone is rough and unequal, where the capsular ligament of the articulation is fixed.—The brims at the upper and back-part of the acetabulum are much larger and higher than anywhere else; which is very necessary to prevent the head of the femur from slipping out of its cavity at this place, where the whole weight of the body bears upon it, and consequently would otherwise be constantly in danger of thrusting it out.—As these brims are extended downwards and forwards, they become less; and at their internal lower part a breach is made in them; from the one side of which to the other, a ligament is placed in the recent subject; under which a large hole is left, which contains a fatty cellular substance and vessels.—Besides this difference in the height of the brims, the acetabulum is otherwise unequal: For the lower internal part of it is depressed below the cartilaginous surface of the upper-part, and is not covered with cartilage; into the upper-part of this particular depression, where it is deepest and of a femoral form, the ligament of the thigh-bone, commonly called the round one, is inserted; while in its more superficial lower part the large mucilaginous gland of this joint is lodged. The largest share of this separate depression is formed in the os ischium.

The osa innominata are joined at their back-part to each side of the os sacrum by a sort of future, with a very thin intervening cartilage, which serves as so much glue to cement these bones together; and strong ligaments go from the circumference of this unequal surface to connect them more firmly. The osa innominata are connected together at their fore-part by the ligamentous cartilage interposed between the two osa pubis.—These bones can therefore have no motion in a natural state, except what is common to the trunk of the body, or to the os sacrum.

Each os innominatum affords a socket (the acetabulum) for the thigh-bones to move in, and the trunk of the body rolls here so much on the heads of the thighs-bones, as to allow the most conspicuous motions of the trunk, which are commonly thought to be performed by the bones of the spine.

The pelvis then has a large open above where it is continued with the abdomen, is strongly fenced by bones on the sides, back, and fore-part, and appears with a wide opening below, in the skeleton; but, in the recent subject, a considerable part of the opening is filled by the sacrosciatic ligaments, pyriform, internal obturator, levatores ani, gemini, and coccygei muscles, which support and protect the contained parts better than bones could have done; so that space is only left at the lowest part of it, for the large excretories, the vesica urinaria, intestinum rectum, and in females, the uterus, to discharge themselves.

The Thorax, or chest, reaches from below the neck to the belly; and, by means of the bones that guard it, is formed into a large cavity: The figure of which is somewhat conoidal.

The bones which form the thorax are the twelve dorsal vertebrae behind, the ribs on the sides, and the sternum before.

The vertebrae have already been described as part of the spine.

The Ribs, or costae, (as if they were custodes, or guards, to those principal organs of the animal machine, the heart and lungs), are the long crooked bones placed at the side of the chest, in an oblique direction downwards in respect of the back-bone.—Their number is generally twelve on each side; though frequently eleven or thirteen have been found.

The ribs are all concave internally; where they are also made smooth by the action of the contained parts, which, on this account, are in no danger of being hurt by them; and they are convex externally, that they might resist that part of the pressure of the atmosphere, which is not balanced by the air within the lungs, during inspiration.—The ends of the ribs next the vertebrae are rounder than they are after these bones have advanced forwards, when they become flatter and broader, and have an upper and lower edge, each of which is made rough by the action of the intercofial muscles, inserted into them.—The upper edge of the ribs is more obtuse and rounder than the lower, which is depressed on its internal side by a long fossa, for lodging the intercofial vessels and nerves; on each side of which there is a ridge, to which the intercofial muscles are fixed. The fossa is not observable however at either end of the ribs: for, at the posterior or root, the vessels have not yet reached the ribs; and, at the fore-end, they are split away into branches, to serve the parts between the ribs.

At the posterior end of each rib, a little head is formed, which is divided by a middle ridge into two plain or hollow surfaces; the lowest of which is the broadest and deepest in most of them. The two plains are joined to the bodies of two different vertebrae, and the ridge forces itself into the intervening cartilage. A little way from this head, we find, on the external surface, a small cavity, where mucilaginous glands are lodged; and round the head, the bone appears spongy, where the capsular ligament of the articulation is fixed.

Immediately beyond this a flatted tubercle rises, with a small cavity at, and roughness about its root, for the articulation of the rib with the transverse process of the lowest of the two vertebrae, with the bodies of which the head of the rib is joined. Advancing further on this external surface, we observe in most of the ribs another smaller tubercle, into which ligaments which connect the ribs to each other, and to the transverse processes of the vertebrae, and portions of the longissimus dorsi, are inserted. Beyond this the ribs are made flat by the sacro-lumbalis muscle, which is inserted into the part of this flat surface farthest from the spine, where each rib makes a considerable curve, called by some its angle. Then the rib begins to turn broad, and continues so to its anterior end, which is hollow and spongy, for the reception of, and firm coalition with the cartilage that runs thence to be inserted into the sternum, or to be joined with some other cartilage.

To the fore-end of each rib a long broad and strong cartilage is fixed, and reaches thence to the sternum, or is joined to the cartilage of the next rib. This course, however, is not in a straight line with the rib; for generally the cartilages make a considerable curve, the concave part of which is upwards; therefore, at their insertion into the sternum, they make an obtuse angle above, and an acute one below. These cartilages, as all others, are firmer and harder internally, than they are on their external surface.

The ribs then are articulated at each end, of which the one behind is doubly joined to the vertebra; for the head is received into the cavities of two bodies of the vertebra, and the larger tubercle is received into the depression in the transverse process of the lower vertebra.

Hitherto we have laid down the general structure and connection of the ribs, and shall next mark their differences.

In viewing the ribs from above downwards, their figure is still straighter; the uppermost being the most crooked of any. Their obliquity, in respect of the spine, increases as they descend; so that though their distances from each other is very little different at their back-part, yet at their fore-ends the distances between the lower ones must increase.

The length of the ribs increases from the first and uppermost rib, as far down as the seventh; and from that to the twelfth, as gradually diminishes. The superior of the two plain, or rather hollow surfaces, by which the ribs are articulated to the bodies of the vertebrae, gradually increases from the first to the fourth rib, and is diminished after that in each lower rib.

The distance of their angles from the heads always increases as they descend to the ninth, because of the greater breadth of the sacro-lumbalis muscle.

The ribs are commonly divided into true and false.

The true costae are the seven upper ones of each side, whose cartilages are all gradually longer as the ribs descend, and are joined to the breast-bone; so that being pressed constantly between two bones, they are flatted at both ends, and are thicker, harder, and more liable to ossify, than the other cartilages that are not subject to so much pressure. These ribs include the heart and lungs; and therefore are the proper or true custodes of life.

The five inferior ribs of each side are the false or bastard, whose cartilages do not reach to the sternum; and therefore, wanting the resistance at their fore-part, they are there pointed; and, on this account, having less pressure, their substance is softer. The cartilages of these false ribs are shorter as the ribs descend.

To all these five ribs the circular edge of the diaphragm is connected; and its fibres, instead of being stretched immediately transversely, and so running perpendicular to the ribs, are pressed so as to be often, especially in expiration, parallel to the plane in which the ribs lie.

The first rib of each side is so situated, that the flat sides are above and below, while one edge is placed inwards, and the other outwards, or nearly so; therefore sufficient space is left above it for the subclavian vessels and muscle; and the broad concave surface is opposed to the lungs. But then, in consequence of this situation, the channel for the intercostal vessels is not to be found, and the edges are differently formed from all the other, except the second; the lower one being rounded, and the other sharp. The head of this rib is not divided into two plain surfaces by a middle ridge, because it is only articulated with the first vertebra of the thorax. Its cartilage is ossified in adults, and is united to the sternum at right angles. Frequently this first rib has a ridge rising near the middle of its posterior edge, where one of the heads of the scalenus muscle rises. Farther forward it is flatted, or sometimes depressed by the clavicle.

The fifth, sixth, and seventh, or rather the sixth, seventh, eighth, and sometimes the fifth, sixth, seventh, eighth, ninth ribs, have their cartilages at least contiguous; and frequently they are joined to each other by crofs cartilages; and most commonly the cartilages of the eighth, ninth, tenth, are connected to the former, and to each other, by firm ligaments.

The eleventh, and sometimes the tenth rib, has no tubercle for its articulation with the transverse process of the vertebra, to which it is only loosely fixed by ligaments. The fossa in its lower edge is not so deep as in the upper ribs, because the vessels run more towards the interface between the ribs. Its fore-end is smaller than its body, and its short small cartilage is but loosely connected to the cartilage of the rib above.

The twelfth rib is the shortest and straightest. Its head is only articulated with the last vertebra of the thorax; therefore is not divided into two surfaces. This rib is not joined to the transverse process of the vertebra, and therefore has no tubercle, being often pulled necessarily inwards by the diaphragm, which an articulation with the transverse process would not have allowed. The fossa is not found at its under edge, because the vessels run below it. The fore-part of this rib is smaller than its middle, and has only a very small pointed cartilage fixed to it. To its whole internal side the diaphragm is connected. The Sternum, or breast-bone, is the broad flat bone or pile of bones, at the fore-part of the thorax.—In adults of a middle age, it is composed of three bones, which easily separate after the cartilages connecting them are destroyed. Frequently the two lower bones are found intimately united; and very often in old people, the sternum is a continued bony substance from one end to the other; though we still observe two, sometimes three, transverse lines on its surface; which are marks of the former divisions.

When we consider the sternum as one bone, we find it broadest and thickest above, and becoming smaller as it descends. The internal surface of this bone is somewhat hollowed for enlarging the thorax; but the convexity on the external surface is not so conspicuous, because the sides are pressed outwards by the true ribs; the round heads of whose cartilages are received into seven smooth pits, formed in each side of the sternum, and are kept firm there by strong ligaments, which, on the external surface, have a particular radiated texture.—The pits at the upper part of the sternum are at the greatest distance from one another, and, as they descend, are nearer; so that the two lowest are contiguous.

The first of the three bones that compose the sternum, all agree, is somewhat of the figure of a heart, as it is commonly painted; only it does not terminate in a sharp point.—This is the uppermost thickest part of the sternum.

The upper middle part of this first bone, where it is thickest, is hollowed, to make place for the trachea arteria; though this cavity is principally formed by the bone being raised on each side of it, partly by the clavicles thrusting it inwards, and partly by the sterno-mastoidei muscles pulling it upwards.—On the outside of each tubercle, there is an oblong cavity, that, in viewing it transversely from before backwards, appears a little convex: Into these glenae the ends of the clavicles are received.—In the side of the under end of this first bone, the half of the pit for the second rib on each side is formed.—The upper part of the surface behind is covered with a strong ligament, which secures the clavicles.

The second or middle division of this bone, is much longer, narrower, and thinner than the first; but, excepting that it is a little narrower above than below, it is nearly equal all over in its dimensions of breadth or thickness.—In the sides of it are complete pits for the third, fourth, fifth, and sixth ribs, and an half of the pits for the second and seventh.

The third bone is much less than the other two, and has only one half of the pit for the seventh rib formed in it; wherefore it might be reckoned only an appendix of the sternum.—In young subjects it is always cartilaginous, and is better known by the name of cartilago xiphoides, or ensiformis, than any other; though the ancients often called the whole sternum ensiforme.—This third bone is seldom of the same figure, magnitude, or situation in any two subjects; for sometimes it is a plain triangular bone, with one of the angles below, and perpendicular to the middle of the upper side, by which it is connected to the second bone.—In other people, the point is turned to one side, or obliquely forwards or backwards.—Frequently it is all nearly of an equal breadth, and in several subjects it is bifurcated; whence some writers give it the name of furcella, or furcula inferior; or else it is unossified in the middle.—In the greatest number of adults it is ossified, and tipped with a cartilage; in some, one half of it is cartilaginous; and in others, it is all in a cartilaginous state.—Generally several oblique ligaments, fixed at one end to the cartilages of the ribs, and by the other to the outer surface of the xiphoid-bone, connect it firmly to those cartilages.

The uses of the sternum are, to afford origin and insertion to several muscles; to sustain the mediastinum, to defend the vital organs, the heart and lungs, at the fore-part; and, lastly, by serving as a moveable fulcrum of the ribs, to assist considerably in respiration.

OF THE SUPERIOR EXTREMITIES.

Each superior extremity is divided into the shoulder, arm, fore-arm, and hand.

The Shoulder consists of the clavicle and scapula.

Clavicle, or collar-bone, is the long crooked bone, in figure like like an Italic J, placed almost horizontally between the upper lateral part of the sternum, and what is commonly called the top of the shoulder, which, as a clavis or beam, it bears off from the trunk of the body.

The clavicle, as well as other long round bones, is larger at its two ends than in the middle. The end next to the sternum is triangular: The angle behind is considerably produced, to form a sharp ridge, to which the transverse ligament extended from one clavicle to the other is fixed.—The side opposite to this is somewhat rounded.—The middle of this protuberant end is as irregularly hollowed, as the cavity in the sternum for receiving it is raised; but, in a recent subject, the irregular concavities of both are supplied by a moveable cartilage, which is not only much more closely connected every where, by ligaments, to the circumference of the articulation, than that of the lower jaw are; but it grows to the two bones at both its internal and external ends; its substance at the internal end being soft, but very strong, and resembling the intervertebral cartilages.

From this internal end the clavicle, for about two fifths of its length, is bended obliquely forwards and downwards. On the upper and fore-part of this curvature a small ridge is seen, with a plain rough surface before it; whence the musculus sternohyoideus and sternomastoideus have in part their origin.—Near the lower angle, a small plain surface is often to be remarked; where the first rib and this bone are contiguous, and are connected by a firm ligament.—From this a rough plain surface is extended outwards, where the pectoral muscle has part of its origin.—Behind, the bone is made flat and rough by the insertion of the larger share of the subclavian muscles.—After the clavicle begins to be bended backwards, it is round, but soon after becomes broad and thin; which shape it retains to its external end.—Along the external concavity, a rough sinuosity runs, from which some part of the deltoid muscle takes its rise:—Opposite to this, on the convex edge, a facetrous ridge gives insertion to a flare of the cucullaris muscle. The upper surface of the clavicle here is flat; but the lower is hollow, for lodging the beginning of the musculus subclavius; and towards its back-part a tubercle rises, to which, and a roughness near it, the strong short thick ligament connecting this bone to the coracoid process of the scapula is fixed.

The external end of this bone is horizontally oblong, smooth, sloping at the posterior side, and tipped in a recent subject with a cartilage, for its articulation with the acromion scapulae.

The medullary arteries, having their direction obliquely outwards, enter the clavicles by one or more small passages in the middle of their back-part.

The triangular unequal interior end of each clavicle, has the cartilage above described interposed betwixt it and the irregular cavity of the sternum.—The ligaments, which surround this articulation to secure it, are so short and strong, that little motion can be allowed any way; and the strong ligament that is stretched across the upper furcula of the sternum, from the posterior prominent angle of the one clavicle, to the same place of the other clavicle, serves to keep each of these bones more firmly in their place.—By the assistance, however, of the moveable intervening cartilage, the clavicle can, at this joint, be raised or depressed, and moved backwards and forwards so much, as that the external end, which is at a great distance from that axis, enjoys very conspicuous motions.

The uses of the clavicles are, to keep the scapulae, and consequently all the superior extremities, from falling in and forward upon the thorax.

Scapula, or shoulder-blade, is the triangular bone situated on the outside of the ribs, with its longest side, called its base, towards the spinal processes of the vertebrae, and with the angle at the upper part of this side about three inches, and the lower angle at a greater distance from these processes.—The back-part of the scapula has nothing but the thin ends of the serratus anterior major, and subscapularis muscles, between it and the ribs: But as this bone advances forwards, its distance from the ribs increases.—The upper, or shortest side, called the superior costa of the scapula, is nearly horizontal, and parallel with the second rib.—The lower side, which is named the inferior costa, is extended obliquely from the third to the eighth rib.—The inferior angle of the scapula is very acute; and the upper one is near to a right angle.—The body of this bone is concave towards the ribs, and convex behind, where it has the name of dorsum.—Three processes are generally reckoned to proceed from the scapula.—The first is the large spine that rises from its convex surface behind, and divides it unequally.—The second process stands out from the fore-part of the upper side; and, from its imaginary resemblance to a crow's beak, is named coracoideus.—The third process is the whole thick bulbous fore-part of the bone.

After thus naming the several constituent parts of the scapula, the particular description will be more easily understood.

The base, which is tipped with cartilage, is not all straight: For, above the spine, it runs obliquely forwards to the superior angle; that here it might not be too protuberant backwards, and so bruise the muscles and teguments: Into the oblique space the musculus patientiae is inserted.—At the root of the spine, on the back-part of the base, a triangular plain surface is formed, by the pressure of the lower fibres of the trapezius.—Below this edge of the scapula is scabrous and rough, for the insertion of the serratus major anticus, and rhomboid muscles.

The back-part of the inferior angle is made smooth by the latissimus dorsi passing over it. This muscle also alters the direction of the inferior costa, some way forwards from this angle; and so far it is flattened behind by the origin of the teres major.—As the inferior costa advances forwards, it is of considerable thickness, is slightly hollowed and made smooth behind by the teres minor, while it has a fossa formed into it below by part of the subscapularis; and between the two a ridge, with a small depression, appears, where the longus extensor cubiti has its origin.

The superior costa is very thin; and near its fore-part there is a semilunar notch, from one end of which to the other a ligament is stretched; and sometimes the bone is continued, to form one, or sometimes two holes, for the passage of the scapular blood-vessels and nerves.—Immediately behind this semilunar cavity, the coraco-hyoid muscle has its rise.—From the notch, to the termination of the fossa for the teres minor, the scapula is narrower than anywhere else, and supports the third process. This part has the name of cervix.

The whole dorsal of the scapula is always said to be convex; but, by reason of the raised edges that surround it, it is divided into two cavities by the spine, which is stretched from behind forwards, much nearer to the superior than to the inferior costa.—The cavity above the spine is concave where the supra-spinatus muscle is lodged; while the surface of this bone below the spine, on which the infra-spinatus muscle is placed, is convex, except a fossa that runs at the side of the inferior costa.

The internal or anterior surface of this bone is hollow, except in the part above the spine, which is convex.—The subscapularis muscle is extended over this surface, where it forms several ridges and intermediate depressions, commonly mistaken for prints of the ribs; they point out the interstices of the bundles of fibres of which the subscapularis muscle is composed.

The spine rises small at the base of the scapula, and becomes higher and broader as it advances forwards.—On the sides it is unequally hollowed and crooked, by the actions of the adjacent muscles.—Its ridge is divided into two rough flat surfaces: Into the upper one, the trapezius muscle is inserted; and the lower one has part of the deltoid fixed to it.—The end of the spine, called acromion, or top of the shoulder, is broad and flat, and is sometimes only joined to the spine by a cartilage.—The anterior edge of the acromion is flat, smooth, and covered with a cartilage, for its articulation with the external end of the clavicle; and it is hollowed below, to allow a passage to the infra and supra-spinati muscles, and free motion to the os humeri. The coracoid process is crooked, with its point inclining forwards; so that a hollow is left at the lower side of its root, for the passage of the infra-spinatus muscle.

The end of this process is marked with three plain surfaces. Into the internal, the serratus minor anticus is inserted: From the external, one head of the biceps flexor cubiti rises; and from the lower one, the coraco-brachialis has its origin.—At the upper part of the root of this process, immediately before the semilunar cavity, a smooth tubercle appears, where a ligament from the clavicle is fixed. From all the external side of this coracoid apophysis, a broad ligament goes out, which becomes narrower where it is fixed to the acromion.

From the cervix scapulae the third process is produced. The fore-part of this is formed into a glenoid cavity, which is of the shape of the longitudinal section of an egg, being broad below, and narrow above.—Between the brims of this hollow, and the fore-part of the root of the spine, a large fissure is left, for the transmission of the supra and infra-spinati muscles; and, on the upper part of these brims, we may remark a smooth surface, where the second head of the biceps flexor cubiti has its origin.—The root of the supercilium is rough all round, for the firmer adhesion of the capsular ligament of the articulation, and of the cartilage which is placed on these brims, where it is thick, but becomes very thin as it is continued towards the middle of the cavity, which it lines all over.

The medullary vessels enter the scapula near the base of the spine.

The scapula and clavicle are joined by plain surfaces, tipped with cartilage; by which neither bone is allowed any considerable motion, being tightly tied down by the common capsular ligament, and by a very strong one which proceeds from the coracoid process; but divides into two before it is fixed into the clavicle, with such a direction, as either can allow this bone to have a small rotation, in which its posterior edge turns more backwards, while the anterior one rises farther forwards; or it can yield to the fore-part of the scapula moving downwards, while the back-part of it is drawn upwards; in both which cases, the oblong smooth articulated surfaces of the clavicle and scapula are not in the same plane, but stand a little transversely, or across each other, and thereby preserve this joint from luxations, to which it would be subject, if either of the bones was to move on the other perpendicularly up and down, without any rotation.—The scapula is connected to the head, os hyoides, vertebrae, ribs, and arm-bone, by muscles, that have one end fastened to these bones, and the other to the scapula, which can move it upwards, downwards, backwards, or forwards; by the quick succession of these motions, its whole body is carried in a circle.

The use of the scapula is, to serve as a fulcrum to the arm; and, by altering its position on different occasions, to allow always the head of the os humeri a right situated socket to move in; and thereby to assist and to enlarge greatly the motions of the superior extremity, and to afford the muscles which rise from it more advantageous actions, by altering their directions to the bone which they are to move.

The Arm has only one bone, best known by the Latin name of os humeri; which is long, round, and nearly straight.

The upper end of this bone is formed into a large, round, smooth head, whose middle point is not in a straight line with the axis of the bone, but stands obliquely backwards from it.—The extent of the head is distinguished by a circular fossa surrounding its base, where the head is united to the bone, and the capsular ligament of the joint is fixed.—Below the fore-part of its base two tubercles stand out: The smallest one, which is situated most to the inside, has the tendon of the subscapularis muscle inserted into it.—The larger more external protuberance is divided, at its upper part, into three smooth plain surfaces; into the anterior of which, the musculus supra-spinatus; into the middle or largest, the infra-spinatus; into the one behind, the teres minor, is inserted.—Between these two tubercles, exactly in the fore part of the bone, a deep long fossa is formed, for lodging the tendinous head of the biceps flexor cubiti.—On each side of this fossa, as it descends in the os humeri, a rough ridge, gently flattened in the middle, runs from the roots of the tubercles.—The tendon of the pectoral muscle is fixed into the anterior of these ridges, and the latissimus dorsi, and teres major, are inserted into the internal one.—A little behind the lower end of this last, another rough ridge may be observed, where the coraco-brachialis is inserted.—From the back-part of the root of the largest tubercle, a ridge also is continued, from which the brevis extensor cubiti rises.—This bone is flattened on the inside, about its middle, by the belly of the biceps flexor cubiti.—In the middle of this plain surface, the entry of the medullary artery is seen slanting obliquely downwards.—At the fore-side of this plane, the bone rises in a sort of ridge, which is rough, and often has a great many small holes in it, where the tendon of the strong deltoid muscle is inserted; on each side of which the bone is smooth and flat, where the brachioceps internus rises. The exterior of these two flat surfaces is the largest; behind it a superficial spiral channel, formed by the muscular nerve and the vessels that accompany it, runs from behind forwards and downwards.—The body of the os humeri is flattened behind by the extensors of the fore-arm.—Near the lower end of this bone, a large sharp ridge is extended on its outside, from which the musculus spinator radii longus, and the longest head of the extensor carpi radialis rise.—Opposite to this, there is another small ridge, to which the aponeurotic tendon, that gives origin to the fibres of the internal and external brachioceps muscles, is fixed; and from a little depression on the fore-side of it, the pronator radii teres rises.

The body of the os humeri becomes gradually broader towards the lower end, where it has several processes; at the roots of which there is a cavity before, and another behind. The anterior is divided, by a ridge, into two; the external, which is the least, receives the end of the radius; and the internal receives the coronoid process of the ulna in the flexion of the fore-arm, while the posterior deep triangular cavity lodges the olecranon in the extensions of that member.—The sides of the posterior cavity are stretched out into two processes, one on each side: These are called condyles; from each of which a strong ligament goes out to the bones of the fore-arm.—The external condyle, which has an oblique direction also forwards in respect of the internal, when the arm is in the most natural posture, is equally broad, and has an obtuse smooth head rising from it forwards.—From the rough part of the condyle, the inferior head of the bicipitis, the extensor digitorum communis, extensor carpi ulnaris, anconeus, and some part of the supinator radii brevis, take their rise; and on the smooth head the upper end of the radius plays.—Immediately on the outside of this, there is a sinuosity made by the shorter head of the bicipitis muscle, upon which the muscular nerve is placed.—The internal condyle is more pointed and protuberant than the external, to give origin to some part of the flexor carpi radialis, pronator radii teres, palmaris longus, flexor digitorum sublimis, and flexor carpi ulnaris.—Between the two condyles, is the trochlea or pully, which consists of two lateral protuberances, and a middle cavity, that are smooth, and covered with cartilage.—When the fore-arm is extended, the tendon of the internal brachioradialis muscle is lodged in the fore-part of the cavity of this pully.—The external protuberance, which is less than the other, has a sharp edge behind; but forwards, this ridge is obtuse, and only separated from the little head, already described, by a small fossa, in which the joined edges of the ulna and radius move.—The internal protuberance of the pully is largest and highest; and therefore, in the motions of the ulna upon it, that bone would be inclined outwards, was it not supported by the radius on that side.—Between this internal protuberance and condyle, a sinuosity may be remarked, where the ulnar nerve passes.

The round head at the upper end of this bone is articulated with the glenoid cavity of the scapula; which being superficial, and having long ligaments, allows the arm a free and extensive motion.

The motions which the arm enjoys by this articulation, are to every side; and by the succession of these different motions, a circle may be described. Besides which, the bone performs a small rotation round its own axis.

The Fore-arm consists of two long bones, the ulna and radius; whose situation, in respect of each other, is oblique in the least straining or most natural posture; that is, the ulna is not directly behind, nor on the outside of the radius, but in a middle situation between these two, and the radius crosses it.—In the following description, by the term posterior is meant that part which is in the same direction with the back of the hand; by anterior, that answering to the palm; by internal, that on the same side with the thumb; by external, the side nearest the little finger.

Ulna, so named from its being used as a measure, is the longest of the two bones of the fore-arm, and situated on the outside of the radius.

At the upper end of the ulna are two processes.—The posterior is the largest, and formed like a hook, whose concave surface moves upon the pully of the os humeri, and is called olecranon, or top of the cubit.—The convex back-part of it is rough and scabrous, where the long-

gus, brevis, and brachioradialis externus, are inserted. The olecranon makes it unnecessary that the tendons of the extensor muscles should pass over the end of the os humeri; which would have been of ill consequence in the great flexions of this joint, or when any considerable external force is applied to this part.—The anterior process is not so large, nor does it reach so high as the one behind; but is sharper at its end, and therefore is named coronoid.—Between these two processes, a large semicircular or sigmoid concavity is left; the surface of which, on each side of a middle rising, is flatting, and exactly adapted to the pully of the bone of the arm.—Across the middle of it, there is a small sinuosity for lodging mucilaginous glands; where, as well as in a small hollow on the internal side of it, the cartilage that lines the rest of its surface is wanting.—Round the brims of this concavity the bone is rough, where the capsular ligament of the joint is implanted.—Immediately below the olecranon, on the back-part of the ulna, a flat, triangular, spongy surface appears, on which we commonly lean.—At the internal side of this, there is a larger hollow surface, where the musculus anconeous is lodged; and the ridge at the inside of this gives rise to the musculus supinator radii brevis.—Between the top of the ridge and the coronoid process, is the semilunar smooth cavity, lined with cartilage, in which, and a ligament extended from the one to the other end of this cavity, the round head of the radius plays.—Immediately below it, a rough hollow gives lodging to mucilaginous glands.—Below the root of the coronoid process, this bone is scarious and unequal, where the brachioradialis internus is inserted.—On the outside of that, we observe a smooth concavity, where the beginning of the flexor digitorum profundus sprouts out.

The body of the ulna is triangular.—The internal angle is very sharp where the ligament that connects the two bones is fixed;—the sides, which make this angle, are flat and rough, by the action and adhesion of the many muscles which are situated here.—At the distance of one third of the length of the ulna from the top, in its fore-part, the passage of the medullary vessels is to be remarked slanting upwards.—The external side of this bone is smooth, somewhat convex, and the angles at each edge of it are blunted by the pressure of the muscles equally disposed about them.

As this bone descends, it becomes gradually smaller; so that its lower end terminates in a little head, standing on a small neck.—Towards the fore and outer part of which last, an oblique ridge runs, that gives rise to the pronator radii quadratus.—The head is round, smooth, and covered with a cartilage on its internal side, to be received into the semilunar cavity of the radius; while a styloid process rises from its outside, to which is fixed a strong ligament that is extended to the os cuneiforme and pisiforme of the wrist.—Between the back-part of that internal smooth side and this process, a sinuosity is left for the tendon of the extensor carpi ulnaris.—On the fore-part of the root of the process, such another depression may be remarked for the passage of the ulnar artery and nerve.—The end of the bone is smooth, and covered with a cartilage.—Between it and the bones of the wrist, a double concave movable cartilage is interposed; which is a continuation of the cartilage that covers the lower end of the radius, and is connected loosely to the root of the styloid process, and to the rough cavity there, in which mucilaginous glands are lodged.

The ulna is articulated above with the lower end of the os humeri, where these bones have depressions and protuberances corresponding to each other, so as to allow an easy and secure extension of the fore-arm to almost a straight line with the arm, and flexion to a very acute angle; but, by the slanting position of the pulley, the lower part of the fore-arm is turned outwards in the extension, and inwards in the flexion; and a very small kind of rotation is likewise allowed in all positions, especially when the ligaments are most relaxed by the forearm being in a middle degree of flexion.—The ulna is also articulated with the radius and carpus, in a manner to be related afterwards.

Radius, so called from its imagined resemblance to a spoke of a wheel, is the bone placed at the inside of the fore-arm. Its upper end is formed into a circular little head, which is hollowed for an articulation with the tubercle at the side of the pulley of the os humeri; and the half of the round circumference of the head next to the ulna is smooth, and covered with a cartilage, in order to be received into the semilunated cavity of that bone.—Below the head, the radius is much smaller; therefore this part is named its cervix, which is made round by the action of the supinator radii brevis.—At the external root of this neck, a tubercle process rises; into the outer part of which the biceps flexor cubiti is inserted.—From this a ridge downwards and inwards, where the supinator radii brevis is inserted; and a little below, and behind this ridge, there is a rough scabrous surface, where the pronator radii teres is fixed.

The body of the radius is not straight, but convex on its internal and posterior surfaces; where it is also made round by the equal pressure of the circumjacent muscles, particularly of the extensors of the thumb; but the surfaces next to the ulna are flattened and rough, for the origin of the muscles of the hand; and both terminate in a common sharp spine, to which the strong ligament extended between the two bones of the fore-arm is fixed. A little below the beginning of the plain surface, on its fore-part, where the flexor muscle of the last joint of the thumb takes its origin, the passage of the medullary vessels is seen slanting upwards.—The radius becomes broader and flatter towards the lower end, especially on its fore-part, where its pronator quadratus muscle is situated.

The lower end of the radius is larger than the superior; though not in such a disproportion as the upper end of the ulna is larger than its lower end.—Its back-part has a flat strong ridge in the middle, and fossae on each side.—In a small groove immediately on the outside of the ridge, the tendon of the extensor tertii interosseus pollicis plays.—In a large one beyond this, the tendons of the indicator and of the common extensor muscles of the fingers pass.—Contiguous to the ulna, there is a small depression made by the extensor minimi digiti,

—On the outside of the ridge there is a broad depression, which seems again subdivided, where the two tendons of the bicipital, or extensor carpi radialis, are lodged.—The internal side of this end of the radius is also hollowed by the extensors of the first and second joint of the thumb; immediately above which, a little rough surface shows where the supinator radii longus is inserted.—The ridges at the sides of the grooves, in which the tendons play, have an annular ligament fixed to them, by which the several sheaths for the tendons are formed.—The fore-part of this end of the radius is also depressed, where the flexors of the fingers and flexor carpi radialis pass.—The external side is formed into a semilunated smooth cavity, lined with a cartilage, for receiving the lower end of the ulna.—The lowest part of the radius is formed into an oblong cavity; in the middle of which is a small transverse rising, gently hollowed, for lodging mucilaginous glands; while the rising itself is inflected into the conjunction of the two bones of the wrist that are received into the cavity.—The internal side of this articulation is fenced by a remarkable process of the radius, from which a ligament goes out to the wrist, as the styloid process of the ulna with its ligament guards it on the outside.

The ends of both the bones of the fore-arm being thicker than the middle, there is a considerable distance between the bodies of these bones; in the larger part of which a strong tendinous, but thin ligament, is extended, to give a large enough surface for the origin of the numerous fibres of the muscles situated here, that are so much sunk between the bones, as to be protected from injuries, which they would otherwise be exposed to.

As the head of the radius receives the tubercle of the os humeri, it is not only bended and extended along with the ulna, but may be moved round its axis in any position; and that this motion round its axis may be sufficiently large, the ligament of the articulation is extended farther down than ordinary on the neck of this bone, before it is connected to it; and it is very thin at its upper and lower part, but makes a firm ring in the middle.—This bone is also joined to the ulna by a double articulation; for above, a tubercle of the radius plays in a socket of the ulna; whilst below, the radius gives the socket, and the ulna the tubercle: But then the motion performed in these two is very different; for, at the upper end, the radius does no more than turn round its axis; while, at the lower end, it moves in a sort of cycloid upon the round part of the ulna; and as the hand is articulated and firmly connected here with the radius, they must move together.—When the palm is turned upward, the radius is said to perform the supination; when the back of the hand is above, it is said to be prone.

The Hand comprehends all from the joint of the wrist to the points of the fingers. Its back-part is convex, for greater firmness and strength; and it is concave before, for containing more surely and conveniently such bodies as we take hold of.

The hand is commonly divided into the carpus, metacarpus, and fingers.

The Carpus is composed of eight small spongy bones, situated at the upper part of the hand, viz. the The scaphoides is situated most internally of those that are articulated with the fore-arm.—The lunare is immediately on the outside of the former.—The cuneiforme is placed still more externally, but does not reach so high up as the other two.—The pisiforme stands forwards into the palm from the cuneiforme.—The trapezium is the first of the second row, and is situated betwixt the scaphoides and first joint of the thumb.—The trapezoides is immediately on the outside of the trapezium.—The os magnum is still more external.—The unciforme is farther to the side of the little finger.

Os scaphoides is the largest of the eight except one. It is convex above, concave and oblong below; from which small resemblance of a boat it has got its name.—Its smooth convex surface is divided by a rough middle fossa, which runs obliquely across it.—The upper largest division is articulated with the radius.—Into the fossa the common ligament of the joint of the wrist is fixed; and the lower division is joined to the trapezium and trapezoides.—The concavity receives more than an half of the round head of the os magnum.—The external side of this hollow is formed into a semilunar plane, to be articulated with the following bone.—The internal, posterior, and anterior edges are rough, for fixing the ligaments that connect it to the surrounding bones.

Os lunare has a smooth convex upper surface, by which it is articulated with the radius.—The internal side, which gives the name to the bone, is in the form of a crescent, and is joined with the scaphoid;—the lower surface is hollow, for receiving part of the head of the os magnum.—On the outside of this cavity is another smooth, but narrow oblong sinuosity, for receiving the upper end of the os unciforme.—On the outside of which a small round convexity is found, for its connection with the os cuneiforme. Between the great convexity above, and the first deep inferior cavity, there is a rough fossa, in which the circular ligament of the joint of the wrist is fixed.

Os cuneiforme is broader above, and towards the back of the hand, than it is below and forwards: which gives it the resemblance of a wedge.—The superior slightly convex surface is included in the joint of the wrist, being opposed to the lower end of the ulna.—Below this, the cuneiform bone has a rough fossa, wherein the ligament of the articulation of the wrist is fixed.—On the internal side of this bone, where it is contiguous to the os lunare, it is smooth and slightly concave.—Its lower surface, where it is contiguous to the os unciforme, is oblong, somewhat spiral, and concave.—Near the middle of its anterior surface, a circular plane appears, where the os pisiforme is sustained.

Os pisiforme is almost spherical, except one circular plane, or slightly hollow surface; which is covered with cartilage for its motion on the cuneiforme bone, from which its whole rough body is prominent forwards into the palm; having the tendon of the flexor carpi ulnaris, and a ligament from the styloid process of the ulna, fixed to its upper part; the transverse ligament of the wrist is connected to its internal side; ligaments extended to the unciform bone, and to the os metacarpi of the little finger, are attached to its lower part; the abductor minimi digiti has its origin from its fore-part; and, at the internal side of it, a small depression is formed, for the passage of the ulnar nerve.

Trapezium has four unequal sides and angles in its back-part, from which it has got its name.—Above, its surface is smooth, slightly hollowed, and semicircular, for its conjunction with the os scaphoides.—Its external side is an oblong concave square, for receiving the following bone.—The inferior surface is formed into a pulley; the two protuberant sides of which are external and internal. On this pulley the first bone of the thumb is moved.—At the external side of the external protuberance, a small oblong smooth surface is formed by the os metacarpi indicis.—The fore-part of the trapezium is prominent in the palm, and, near to the external side, has a sinuosity in it, where the tendon of the flexor carpi radialis is lodged; on the ligamentous sheath of which the tendon of the flexor tertii intermarii pollicis plays: And still more externally the bone is scarious, where the transverse ligament of the wrist is connected, the abductor and flexor primi intermarii pollicis have their origin, and ligaments go out to the first bone of the thumb.

Os trapezoides, so called from the irregular quadrangular figure of its back-part, is the smallest bone of the wrist, except the pisiforme.—The figure of it is an irregular cube.—It has a small hollow surface above, by which it joins the scaphoides; a long convex one internally, where it is contiguous to the trapezium; a small external one, for its conjunction with the os magnum; and an inferior convex surface, the edges of which are however so raised before and behind, that a sort of pulley is formed, where it sustains the os metacarpi indicis.

Os magnum, so called because it is the largest bone of the carpus, is oblong, having four quadrangular sides, with a round upper end, and a triangular plain one below.—The round head is divided by a small rising, opposite to the connection of the os scaphoides and lunare, which together form the cavity for receiving it.—On the inside, a short plain surface joins the os magnum to the trapezoides.—On the outside is a long narrow concave surface, where it is contiguous to the os unciforme.—The lower end, which sustains the metacarpal bone of the middle finger, is triangular, slightly hollowed, and farther advanced on the internal side than on the external, having a considerable oblong depression made on the advanced inside by the metacarpal bone of the fore-finger; and generally there is a small mark of the os metacarpi digiti annularis on its external side.

Os unciforme has got its name from a thin broad process that stands out from it forwards into the palm, and is hollow on its inside, for affording passage to the tendons of the flexors of the fingers. To this process also the transverse ligament is fixed, that binds down and defends these tendons; and the flexor and abductor muscles of the little finger have part of their origin from it.—The upper plain surface is small, convex, and joined with the os lunare.—The internal side is long, and slightly convex, adapted to the contiguous os magnum: The external surface is oblique, and irregularly convex, to be articulated with the cuneiform bone:—The lower end is divided into two concave surfaces; the external is joined with the metacarpal bone of the little finger, and the internal one is fitted to the metacarpal bone of the ring-finger.

The uses of the carpus are, to serve as a base to the hand, to protect its tendons, and to afford it a free large motion.

Metacarpus consists of four bones, which sustain the fingers.—Each bone is long and round, with its ends larger than its body.—The upper end, which some call the base, is flat and oblong, without any considerable head or cavity; but it is however somewhat hollowed, for the articulation with the carpus: It is made flat and smooth on the sides where these bones are contiguous to each other.—Their bodies are flattened on their back-part by the tendons of the extensors of the fingers.—The anterior surface of these bodies is a little concave, especially in their middle; along which a sharp ridge stands out, which separates the musculi interossei placed on each side of these bones, which are there made flat and plain by these muscles.

Their lower ends are raised into large oblong smooth heads, whose greatest extent is forwards from the axis of the bone.—At the fore-part of each side of the root of each of these heads, one or two tubercles stand out, for fixing the ligaments that go from one metacarpal bone to another, to preserve them from being drawn aside:—Round the heads a rough ring may be remarked, for the capsular ligaments of the first joints of the fingers to be fixed to; and both sides of these heads are flat, by pressing on each other.

The concavity on the fore-part of these metacarpal bones, and the placing their basis on the arched carpus, cause them to form a hollow in the palm of the hand, which is useful often to us.—The spaces between them lodge muscles, and their small motion makes them fit supporters for the fingers to play on.

Though the os meta carpi fo far agree, yet they may be distinguished from each other by the following marks.

The os metacarpi indicis is generally the longest.—Its base, which is articulated with the os trapezoides, is hollow in the middle.—The small ridge on the internal side of this oblong cavity is smaller than the one opposite to it, and is made flat on the side by the trapezium.—The exterior ridge is also smooth, and flat on its outside, for its conjunction with the os magnum; immediately below which, a semicircular smooth flat surface shews the articulation of this to the second metacarpal bone.—The back-part of this base is flattened, where the long head of the extensor carpi radialis is inserted; and its fore-part is prominent, where the tendon of the flexor carpi radialis is fixed.—The external side of the body of this bone is more hollowed by the action of muscles, than the internal.—The tubercle at the internal root of its head is larger than the external.—Its base is so firmly fixed to the bone it is connected with, that it has no motion.

Os metacarpi medii digiti is generally the second in length.—Its base is a broad superficial cavity, slanting outwards; the internal posterior angle of which is so prominent, as to have the appearance of a process.—The internal side of this base is made plain in the same way as the external side of the former bone, while its external side has two hollow circular surfaces, for joining the third metacarpal bone; and between these surfaces there is a rough fossa, for the adhesion of a ligament, and lodging mucilaginous glands.—The shorter head of the bicornis is inserted into the back-part of this base.—The two sides of this bone are almost equally flattened; only the ridge on the fore-part of the body inclines outwards.—The tubercles at the fore-part of the root of the head are equal.—The motion of this bone is very little more than the first metacarpal one has; and therefore these two firmly resist bodies pressed against them by the thumb, or fingers, or both.

Os metacarpi digitii annularis is shorter than the second metacarpal bone.—Its base is semicircular and convex, for its conjunction with the os unciforme.—On its internal side are two smooth convexities, and a middle fossa, adapted to the second metacarpal bone.—The external side has a triangular smooth concave surface to join it with the fourth one. The anterior ridge of its body is situated more to the out than to the inside.—The tubercles near the head are equal.—The motion of this third metacarpal bone is greater than the motion of the second.

Os metacarpi minimi digiti is the smallest and sharpest.—Its base is irregularly convex, and rises slanting outwards.—Its internal side is exactly adapted to the third metacarpal bone.—The external has no smooth surface, because it is not contiguous to any other bone; but it is prominent where the extensor carpi ulnaris is inserted.—As this metacarpal bone is furnished with a proper moving muscle, has the plainest articulation, is most loosely connected and least confined, it not only enjoys a much larger motion than any of the rest, but draws the third bone with it, when the palm of the hand is to be made hollow by its advancement forwards, and by the prominence of the thumb opposite to it.

The Thumb and four Fingers are each composed of three long bones.

The thumb is situated obliquely in respect of the fingers, neither opposite directly to them, nor in the same plane with them.—All its bones are much thicker and stronger in proportion to their length, than the bones of the fingers are: Which was extremely necessary, since the thumb counteracts all the fingers.

The first bone of the thumb has its base adapted to the double pulley of the trapezium.—The edge at the fore-part of this base is produced farther than any other part; and round the back-part of the base a rough fossa may be seen, for the connection of the ligaments of this joint.—The body and head of this bone are of the same shape as the os meta carpi: only that the body is shorter, and the head flatter, with the tubercles at the fore-part of its root larger.

The articulation of the upper end of this bone is uncommon: For though it has protuberances and depressions adapted to the double pulley of the trapezium; yet it enjoys a circular motion, as the joints do where a round head of one bone plays in the orbicular socket of another; only it is somewhat more confined and less expedient, but stronger and more secure, than such joints generally are.

The second bone of the thumb has a large base formed into an oblong cavity, whose greatest length is from one side to the other.—Round it several tubercles may be remarked, for the insertion of ligaments.—Its body is convex, or a half-round behind; but flat before, for lodging the tendon of the long flexor of the thumb, which is tied down by ligamentous sheaths that are fixed on each side to the angle at the edge of this flat surface.

The articulation and motion of the upper end of this second bone is as singular as that of the former.—For its cavity being joined to the round head of the first bone, it would seem at first view to enjoy motion in all directions; yet, because of the strength of its lateral ligaments, oblong figure of the joint itself, and mobility of the first joint, it only allows flexion and extension; and these are generally much confined.

The third bone of the thumb is the smallest, with a large base, whose greatest extent is from one side to the other.—This base is formed into two cavities and a middle protuberance, to be adapted to the pulley of the former bone.—Its body is rounded behind; but is flatter than in the former bone, for sustaining the nail.—It is flat and rough before, by the insertion of the flexor tertii internodii.—This bone becomes gradually smaller, till near the lower end, where it is a little enlarged, and has an oval scabrous edge.

The motion of this third bone is confined to flexion and extension.

The orderly disposition of the bones of the fingers into three rows, has made them generally obtain the name of three phalanges.—All of them have half-round convex surfaces, covered with an aponeurosis, formed by the tendons of the extensors, lumbricales, and interossei, and placed directly backwards, for their greater strength; and their flat concave part is forwards, for taking hold more surely, and for lodging the tendons of the flexor muscles.—The ligaments for keeping down these tendons are fixed to the angles that are between the convex and concave sides.

The bones of the first phalanx of the fingers answer to the description of the second bone of the thumb: only that the cavity in their base is not so oblong; nor is their motion on the metacarpal bones so much confined; for they can be moved laterally or circularly, but have no rotation, or a very small degree of it, round their axis.

The second bone of the fingers has its base formed into two lateral cavities, and a middle protuberance; while the lower end has two lateral protuberances, and a middle cavity; therefore it is joined at both ends in the same manner, which none of the bones of the thumb are.

The third bone differs nothing from the description of the third bone of the thumb, excepting in the general distinguishing marks; and therefore the second and third phalanx of the fingers enjoy only flexion and extension.

All the difference of the phalanges of the several fingers consists in their magnitude.—The bones of the middle-finger being the longest and largest.—Those of the fore-finger come next to that in thickness, but not in length, for those of the ring-finger are a little longer. The little finger has the smallest bones. Which disposition is the best contrivance for holding the largest bodies; because the longest fingers are applied to the middle largest periphery of such substances as are of a spherical figure.

The uses of all the parts of our superior extremities are so evident in the common actions of life, that it is needless to enumerate them here; and therefore we shall proceed to the last part of the skeleton.

OF THE INFERIOR EXTREMITIES.

The Inferior Extremities depend from the acetabula of the osa innominata; are commonly divided into three parts, viz. the thigh, legs, and feet.

The Thigh has only one bone; which is the longest of the body. The situation of it is not perpendicular; for the lower end is inclined considerably inwards: So that the knees are almost contiguous, while there is a considerable distance between the thigh-bones above: Which is of good use to us, since sufficient space is thereby left for the external parts of generation, the two great cloaca of urine and feces, and for the large thick muscles that move the thigh inwards: And, at the same time, this situation of the thigh-bones renders our progression quicker, surer, straighter, and in less room.

The upper end of the thigh-bone is not continued in a straight line with the body of it, but is set off obliquely inwards and upwards, whereby the distance here between these two bones at their upper part is considerably increased.—This end is formed into a large smooth round head, which is the greater portion of a sphere unequally divided.—Towards its lower internal part, a round rough spongy pit is observable, where the strong ligament, commonly called the round one, is fixed, to be extended from thence to the lower internal part of the receiving cavity, where it is considerably broader than near to the head of the thigh-bone.—The small part below the head, called the cervix, of the os femoris, has a great many large holes, into which the fibres of the strong ligament, continued from the capular, enter, and are thereby surely united to it; and round the root of the neck, where it rises from the bone, a rough ridge is found, where the capular ligament of the articulation itself is connected.—Below the back-part of this root, the large unequal protuberance, called trochanter major, stands out; the external convex part of which is distinguished into three different surfaces, whereof the one on the fore-part is scabrous and rough, for the insertion of the gluteus minimus; the superior one is smooth, and has the gluteus medius inserted into it; and the one behind is made flat and smooth by the tendon of the gluteus maximus passing over it.—The upper edge of this process is sharp and pointed at its back-part, where the gluteus medius is fixed; but forwards it is more obtuse, and has two superficial pits formed in it: Into the superior of these, the piriformis is implanted; and the obturator internus and gemini are fixed into the lower one. one.—From the backmost prominent part of this great trochanter, a rough ridge runs backwards and downwards, into which the quadratus is inferted.—In the deep hollow, at the internal upper side of this ridge, the obturator externus is implanted.—More internally, a conoid process, called trochanter minor, rises, for the insertion of the musculus psoas and iliacus internus, and the pectineus is implanted into a rough hollow below its internal root.—The muscles inserted into these two processes being the principal instruments of the rotatory motion of the thigh, have occasioned the name of trochanters to the processes.

The body of the os femoris is convex on the fore-part, and made hollow behind, by the action of the muscles that move it and the leg, and for the convenience of fitting, without bearing too much on these muscles.—The fore-part of the thigh-bone is a little flattened above by the beginning of the cruralis muscle, as it is also below by the same muscle and the rectus.—Its external surface is likewise made flat below by the vastus externus, where it is separated from the former by an obtuse ridge.—The vastus internus depresses a little the lower part of the internal surface.—The posterior concave surface has a ridge rising in its middle, commonly called linea aspera, into which the triceps is inserted, and the short head of the biceps flexor tibie rises from it.—At the upper part of it, the medullary vessels enter by a small hole that runs obliquely upwards.—A little above which, there is a rough fossa or two, where the tendon of the gluteus maximus is fixed.—The lower end of the linea aspera divides into two, which descend towards each side.—The two vasti muscles have part of their origin from these ridges; and the long tendon of the triceps is fixed to the internal, by means of part of the falcia aponeurotica of the thigh.—Near the beginning of the internal ridge, there is a discontinuation of the ridge, where the crural artery passes through the aponeurosis.—Between these two rough lines, the bone is made flat by the large blood-vessels and nerves which pass upon it; and near the end of each of these ridges, a small smooth protuberance may often be remarked, where the two heads of the external gastrocnemius muscle take their rise; and from the fore-part of the internal tubercle, a strong ligament is extended to the inside of the tibia.

The lower end of the os femoris is larger than any other part of it, and is formed into a great protuberance on each side, called its condyles; between which a considerable cavity is found, especially at the back-part, in which the crural vessels and nerves lie immersed in fat.—The internal condyle is longer than the external.—Each of these processes seems to be divided in its plain smooth surface. The mark of division on the external is a notch, and on the internal a small protuberance. The fore-part of this division, on which the rotula moves, is formed like a pulley, the external side of which is highest.—Behind, there are two oblong large heads, whose greatest extent is backwards, for the motion of the tibia; and from the rough cavity between them, but near to the base of the internal condyle, the strong ligament, commonly called the crois one, has its rise.—A little above which, a rough protuberance gives insertion to the tendon of the triceps.—The condyles, both on the outer and inner side of the knee, are made flat by the muscles passing along them.—On the back part of the internal, a slight depression is made by the tendons of the gracilis and sartorius; and on the external, such another is formed by the biceps flexor cruris; behind which, a deep fossa is to be observed, where the popliteus muscle has its origin.—From the tubercle immediately before this cavity, a strong round ligament goes out to the upper part of the fibula.—Round this lower end of the thigh-bone, large holes are found, into which the ligaments for the security of the joint are fixed, and blood-vessels pass to the internal subfascia of the bone.

The thigh-bone being articulated above with the acetabulum of the os innominata, which affords its round head a secure and extensive play, can be moved to every side; but is restrained in its motion outwards by the high brims of the cavity, and by the round ligament; for otherwise the head of the bone would have been frequently thrust out at the breach of the brims on the inside, which allows the thigh to move considerably inwards.—The body of this bone enjoys little or no rotatory motion, though the head most commonly moves round its own axis; because the oblique progress of the neck and head from the bone is such, that the rotatory motion of the head can only bring the body of the bone forwards and backwards.—The os femoris is articulated below to the tibia and rotula in the manner afterwards to be described.

The nearness of the small neck to the round head of the thigh-bone, and its upper end being covered with very thick muscles, make greater difficulty in distinguishing between a luxation and fracture here, than in any other part of the body.

The Leg is composed of three bones, tibia, fibula, and rotula.

Tibia, so called from its resemblance to an old musical pipe or flute, is the long, thick, triangular bone, situated at the internal part of the leg, and continued in almost a straight line from the thigh-bone.

The upper end of the tibia is large, bulbous, and spongy, and is divided into two cavities by a rough irregular protuberance, which is hollow at its most prominent part, as well as before and behind. The anterior of the two ligaments that compose the great crois one, is inserted into the middle cavity, and the depression behind receives the posterior ligament.—The two broad cavities at the sides of this protuberance are not equal; for the internal is oblong and deep, to receive the internal condyle of the thigh-bone; while the external is more superficial and rounder, for the external condyle.—In each of these two cavities of a recent subject, a semilunar cartilage is placed, which is thick at its convex edge, and becomes gradually thinner towards the concave or interior edge.—The middle of each of these cartilages is broad, and the ends of them turn narrower and thinner, as they approach the middle protuberance of the tibia.—The thick convex edge of each cartilage is connected to the capsular and other ligaments of the articulation, but so near to their rise from the tibia, that the cartilages cartilages are not allowed to change place far; while the narrow ends of the cartilages, becoming almost ligaments, are fixed at the insertion of the strong cross ligament into the tibia, and seem to have their sublimate united with it; therefore a circular hole is left between each cartilage and the ligament, in which the most prominent convex part of each condyle of the thigh-bone moves.—The circumference of these cavities is rough and unequal, for the firm connection of the ligaments of the joint.—Immediately below the edge, at its back-part, two rough flatted protuberances stand out: Into the internal, the tendon of the semimembranosus muscle is inserted; and a part of the cross ligament is fixed to the external.—On the outside of this last tubercle, a smooth slightly-hollowed surface is formed by the action of the popliteus muscle.

Below the fore-part of the upper end of the tibia, a considerable rough protuberance rises, to which the strong tendinous ligament of the rotula is fixed.—On the internal side of this, there is a broad, scabrous, slightly-hollowed surface, to which the internal long ligament of the joint, the aponeurosis of the vastus internus, and the tendons of the semimembranosus, gracilis, and sartorius, are fixed.—Below the external edge of the upper end of the tibia, there is a circular flat surface, covered, in a recent subject, with cartilage, for the articulation of the fibula;—between which and the anterior knob, there is a rough hollow, from which the tibialis anticus, and extensor digitorum longus, take their origin.—From the smooth flat surface, a ridge runs obliquely downwards and inwards, to give rise to part of the soleus, tibialis posterior, and flexor digitorum longus, and insertion to the aponeurosis of the semimembranosus which covers the popliteus, and to some of the external fibres of this last named muscle.—At the inside of this ridge an oblique plain surface is left, where the greatest part of the musculus popliteus is inserted.—The remaining body of the tibia is triangular.—The anterior angle is very sharp, and is commonly called the spine or shin. This ridge is not straight; but turns first inwards, then outwards, and lastly inwards again.—The plain internal side is smooth and equal, being little subjected to the actions of muscles; but the external side is hollowed above by the tibialis anticus, and below by the extensor digitorum longus, and extensor pollicis longus.—The two angles behind these sides are rounded by the action of the muscles;—the posterior side comprehended between them is not so broad as those already mentioned, but is more oblique and flatted by the action of the tibialis posterior and flexor digitorum longus.—Some way above the middle of the bone, the internal angle terminates, and the bone is made round by the pressure of the musculus soleus.—Near to this, the passage of the medullary vessels is seen slanting obliquely downwards.

The lower end of the tibia is made hollow, but so as a small protuberance rises in the middle.—The internal side of this cavity, which is smooth, and, in a recent subject, is covered with cartilage, is produced into a considerable process, commonly named malleolus internus; the point of which is divided by a notch, and from it ligaments are sent out to the foot.—The external side of this end of the tibia has a rough irregular semilunar cavity formed in it, for receiving the lower end of the fibula.—The posterior side has two lateral grooves, and a small middle protuberance. In the internal depression, the tendons of the musculus tibialis posterior, and flexor digitorum longus, are lodged; and in the external, the tendon of the flexor longus pollicis plays.—From the middle protuberance, ligamentous sheaths go out, for tying down these tendons.

Fibula is the small long bone, placed on the outside of the leg, opposite to the external angle of the tibia; the shape of it is irregularly triangular.

The head of the fibula has a superficial circular cavity formed on its inside, which, in a recent subject, is covered with a cartilage, but so closely connected to the tibia by ligaments, as to allow only a small motion backwards and forwards.—This head is protuberant and rough on its outside, where a strong round ligament, and the musculus biceps, are inserted; and, below the back-part of its internal side, a tubercle may be remarked, that gives rise to the strong tendinous part of the soleus muscle.

The body of this bone is a little crooked inwards and backwards, which figure is owing to the actions of the muscles; but is still further increased by nurses, who often hold children carelessly by the legs.—The sharpest angle of the fibula is forwards, on each side of which the bone is considerably, but unequally, depressed by the bellies of the several muscles that rise from, or act upon it; and, in old people, these muscles make distinct sinuities for themselves.—The external surface of the fibula is depressed obliquely from above downwards and backwards, by the two peronaei.—Its internal surface is unequally divided into two narrow longitudinal planes, by an oblique ridge extended from the upper part of the anterior angle, to join with the lower end of the internal angle. To this ridge the ligament stretched between the two bones of the leg is connected.—The anterior of the two planes is very narrow above, where the extensor longus digitorum, and extensor longus pollicis, arise from it; but is broader below, where it has the print of the nonus Vealii.—The posterior plane is broad and hollow, giving origin to the larger share of the tibialis posterior.—The internal angle of this bone has a tendinous membrane fixed to it, from which fibres of the flexor digitorum longus take their rise.—The posterior surface of the fibula is the plainest and smoothest, but is made flat above by the soleus, and is hollowed below by the flexor pollicis longus.—In the middle of this surface the canal for the medullary vessels may be seen slanting downwards.

The lower end of the fibula is extended into a spongy oblong head, on the inside of which is a convex, irregular, and frequently a scabrous surface, that is received by the external hollow of the tibia, and so firmly joined to it by a very thin intermediate cartilage and strong ligaments, that it scarce can move.—Below this, the fibula is stretched out into a coronoid process, that is smooth, covered with cartilage on its internal side, and is there contiguous to the outside of the first bone of the foot, the astragalus, to secure the articulation. This process, named malleolus externus, being situated farther back back than the internal malleolus, and in an oblique direction, obliges us naturally to turn the fore-part of the foot outwards. At the lower internal part of this process, a spongy cavity for mucilaginous glands may be remarked; from its point, ligaments are extended to the astragalus, os calcis, and os naviculare, bones of the foot; and from its inside, short strong ones go out to the astragalus. On the back-part of it, a sinuosity is made by the tendons of the peronei muscles.—When the ligament extended over these tendons from the one side of the depression to the other is broke, stretched too much, or made weak by a sprain, the tendons frequently start forwards to the outside of the fibula.

The conjunction of the upper end of the fibula with the tibia is, by plain surfaces, tipped with cartilage; and, at its lower end, the cartilage seems to glue the two bones together, not, however, so firmly in young people, but that the motion at the other end of such a long radius is very observable.

The principal use of this bone is to afford origin and insertion to muscles; the direction of which may be a little altered, on proper occasions, by its upper part shifting backwards and forwards.—It likewise helps to make the articulation of the foot more secure and firm.

**Rotula** is the small flat bone situated at the fore-part of the joint of the knee.—Its shape resembles the common figure of the heart with its point downwards.—The anterior convex surface of the rotula is pierced by a great number of holes, into which fibres of the strong ligament that is spread over it enter.—Behind, its surface is smooth, covered with cartilage, and divided by a middle convex ridge into two cavities, of which the external is largest, and both are exactly adapted to the pulley of the os femoris, on which they are placed in the most ordinary untraining postures of the leg; but when the leg is much bended, the rotula descends far down on the condyles; and when the leg is fully extended, the rotula rises higher, in its upper part, than the pulley of the thigh-bone.—The plain smooth surface is surrounded by a rough prominent edge, to which the capsular ligament adheres:—Below, the point of the bone is scabrous, where the strong tendinous ligament from the tubercle of the tibia is fixed.—The upper horizontal part of this bone is flatted and unequal, where the tendons of the extensors of the leg are inserted.

The substance of the rotula is cellular, with very thin external firm plates: But then these cells are so small, and such a quantity of bone is employed in their formation, that scarce any bone of its bulk is so strong. Besides, it is covered all over with a thick ligament, to connect its substance, and is moveable to one side or other; therefore is sufficiently strong to resist the ordinary actions of the large muscles that are inserted into it, or any common external force applied to it.

The parts which constitute the joint of the knee being now described, let us examine what are its motions, and how performed.—The two principal motions are flexion and extension.—In the former of these, the leg may be brought to a very acute angle with the thigh, by the condyles of the thigh-bones being round and made smooth far backwards. In performing this, the rotula is pulled down by the tibia.—When the leg is to be extended, the rotula is drawn upwards, consequently the tibia forwards, by the extensor muscles; which, by means of the protuberant joint, and of this thick bone with its ligament, have in effect the chord, with which they act, fixed to the tibia at a considerable angle, therefore act with advantage; but are restrained from pulling the leg farther than to a straight line with the thigh, by the posterior part of the crois ligament, that the body might be supported by a firm perpendicular column: For at this time the thigh and leg are as little movable in a rotatory way, or to either side, as if they were one continued bone.—But when the joint is a little bended, the rotula is not tightly braced, and the posterior ligament is relaxed; therefore this bone may be moved a little to either side, or with a small rotation in the superficial cavities of the tibia; which is done by the motion of the external cavity backwards and forwards, the internal serving as a sort of axis. Seeing then one part of the crois ligament is situated perpendicularly, and the posterior part is stretched obliquely from the internal condyle of the thigh outwards, that posterior part of the crois ligament prevents the leg's being turned at all inwards; but it could not hinder it from turning outwards almost round, was not that motion confined by the lateral ligaments of this joint, which can yield little.

The Foot is divided into three parts, viz. tarfur, metatarfur, and toes: In the description of which, the broad of the foot shall be called superior; the sole, inferior; the side on which the great toe is, internal; that where the little toe is, external.

The tarfur consists of seven spongy bones; to wit, the astragalus, os calcis, naviculare, cuboides, cuneiforme externum, cuneiforme medium, and cuneiforme internum.

The astragalus is the uppermost of these bones.—The os calcis is below the astragalus, and is considerably prominent backwards beyond the other bones, to form the heel.—The os naviculare is in the middle of the internal side of the tarfur.—The os cuboides is the most external of the row of four bones at its fore-part.—The os cuneiforme externum is placed at the inside of the cuboid.—The cuneiforme medium is between the external and internal cuneiform bones, and the internal cuneiform is put at the internal side of the foot.

In the description of these bones, let it be observed, That wherever a ridge is mentioned, without a particular use assigned, a ligament is understood to be fixed to it: or where a spongy rough cavity, depression, or fossa, is remarked, without naming its use, a ligament is inserted, and mucilaginous glands are lodged.

The upper part of the astragalus is formed into a large smooth head, which is slightly hollowed in the middle; and therefore resembles a superficial pulley, by which it is fitted to the lower end of the tibia.—The internal side of this head is flat and smooth, to play on the internal malleolus.—The external side has also such a surface, but larger, for its articulation with the external malleolus.—Round the base of this head there is a rough fossa; and, immediately before the head, as also below its internal smooth surface, we find a considerable rough cavity.

The lower surface of the astragalus is divided by an irregular, deep, rough fossa; which, at its internal end, is narrow, but gradually widens, as it stretches obliquely outwards and forwards.—The smooth surface, covered with cartilage, behind this fossa, is large, oblong, extended in the same oblique situation with the fossa, and concave, for its conjunction with the os calcis.—The back-part of the edge of this cavity is produced into two sharp-pointed rough processes, between which is a depression, made by the tendon of the flexor pollicis longus.

—The lower surface before the fossa is convex, and composed of three distinct smooth planes. The long one behind, and the exterior or shortest, are articulated with the heel-bone; while the internal, which is the most convex of the three, rests and moves upon a cartilaginous ligament, that is continued from the calcaneum to the os scaphoideum.

The fore-part of this bone is formed into a convex oblong smooth head, which is received by the os naviculare.—Round the root of this head, especially on the upper surface, a rough fossa may be remarked.

The astragalus is articulated above to the tibia and fibula, which together form one cavity. Though, in this articulation, the bones have prominences and cavities so small, as might allow motions in all directions; yet the flexion and extension are the most considerable, the other motions being confined by the malleoli, and by the strong ligaments which go out from the points of these processes to the astragalus and os calcis. The astragalus is joined below to the os calcis; and before, to the os naviculare, in the manner to be explained when these bones are described.

Calcaneum is the largest bone of the seven.—Behind, it is formed into a large knob, commonly called the heel: The surface of which is rough behind, where the tendo Achillis is inserted into it; and above, it is hollow and spongy. Farther forwards, on the upper surface of the calcaneum, there is an irregular, oblong, smooth convexity, adapted to the concavity at the back-part of the astragalus: And beyond this a narrow fossa is seen, which divides it from two small concave smooth surfaces, that are joined to the fore-part of the astragalus.—Behind the posterior of these smooth surfaces, which is the largest, a small sinuosity is made by the tendon of the flexor digitorum longus; at the fore-part of which a small rough protuberance appears, that gives rise to the musculus extensor digitorum brevis.

The external side of this bone is flat, with a superficial fossa running horizontally, in which the tendon of the musculus peronaeus longus is lodged.—The internal side of the heel-bone is hollowed, for lodging the origin of the mallea cornea Jac. Sylvii, and for the safe passage of tendons, nerves, and arteries.—Under the side of the internal smooth concavity, a particular groove is made by the tendon of the flexor pollicis longus; and from the thin protuberance on this internal side, the cartilaginous ligament that supports the astragalus, goes out to the os naviculare; on which ligament, and on the edge of this bone to which it is fixed, the groove is formed for the tendon of the flexor digitorum profundus.

The lower surface of this bone is pressed flat at the back-part, by the weight of our bodies; and immediately before this plane, there are two tubercles, from the internal of which the musculus abductor pollicis, flexor digitorum sublimis, as also part of the aponeurosis plantaris, and of the abductor minimi digiti, have their origin; and the other part of the abductor minimi digiti and aponeurosis plantaris, rises from the external.

Before these protuberances this bone is concave, for lodging the flexor muscles; and at its fore-part we may observe a rough depression, from which, and a tubercle behind it, the ligament goes out that prevents this bone to be separated from the os cuboides.

The fore-part of the os calcis is formed into an oblong, pulley-like, smooth surface, which is circular at its upper external end, but is pointed below. This smooth surface is fitted to the os cuboides.

Though the surfaces by which the astragalus and os calcis are articulated, seem fit enough for motion; yet the very strong ligaments by which these bones are connected, prevent it, and render this principal part of our base, which rests on the ground, to wit, the os calcis, firm.

Os naviculare, is somewhat circular.—It is formed into an oblong concavity behind, for receiving the anterior head of the astragalus.—On the upper surface, there is a rough fossa.—Below, the os naviculare is very unequal and rough; but hollow for the safety of the muscles.—On its inside, a large knob rises out, from which the abductor pollicis takes in part its origin, the tendon of the tibialis pollicis is inserted into it, and to it two remarkable ligaments are fixed; the first is the strong one, formerly mentioned, which supports the astragalus; the second is stretched from this bone obliquely across the foot, to the metatarsal bones of the middle toe, and of the toe next to the little one.—On the outside of the os naviculare, there is a semicircular smooth surface, where it is joined to the os cuboides.—The fore-part of this bone is all covered with cartilage, and is divided into three smooth planes, fitted to the three ossa cuneiformia.

The os naviculare and astragalus are joined as a ball and socket, and the naviculare moves in all directions in turning the toes inwards, or in raising or depressing either side of the foot, though the motions are greatly restrained by the ligaments which connect this to the other bones of the tarsus.

Os cuboides is a very irregular cube.—Behind, it is formed into an oblong unequal concavity, adapted to the fore-part of the os calcis.—On its internal side, there is a small semicircular smooth cavity, to join the os naviculare.—Immediately before which, an oblong smooth plane is made by the os cuneiforme externum.—Below this, the bone is hollow and rough.—On the internal side of the lower surface, a round protuberance and fossa are found, where the musculus adductor pollicis has its origin. On the external side of this same surface, there is a round knob, covered with cartilage; immediately before which, a smooth fossa may be observed, in which the tendon of the peronaeus primus runs obliquely across the the foot; and on the knob, the thin flat cartilage proper to this muscle plays; in place of which, sometimes a bone is found:—More externally than the knob, a rough hollow is made, for the strong ligaments stretched between this bone and the os calcis.—Before, the surface of the os cuboides is flat, smooth, and slightly divided into two planes, for sustaining the os metatarsi of the little toe, and of the toe next to it.

The form of the back-part of the os cuboides, and the ligaments connecting the joint there with the os calcis, both concur in allowing little motion in this part.

Os cuneiforme externum, is much of the shape of a wedge, being broad and flat above, with long sides running obliquely downwards, and terminating in a sharp edge.—The upper surface of this bone is an oblong square.—The one behind is nearly a triangle, but not complete at the inferior angle, and is joined to the os naviculare.—The external side is an oblong square, divided as it were by a diagonal: The upper half of it is smooth, for its conjunction with the os cuboides: The other is a scabrous hollow; and in its superior anterior angle, a small smooth impression is made by the os metatarsi of the toe next to the little one.—The internal side of this bone is also quadrangular, with the fore-part of its edge made flat and smooth by the os metatarsi of the toe next to the great one; and the back-part is also flat and smooth, where the os cuneiforme medium is contiguous to it.—The fore-part of this bone is an oblong triangle, for sustaining the os metatarsi of the middle toe.

Os cuneiforme medium, or minimum, is still more exactly the shape of a wedge than the former.—Its upper part is square;—its internal side has a flat smooth surface above and behind, for its conjunction with the following bone; with a small rough fossa below; and a considerable share of it is rough and hollow.—The external side is smooth and a little hollowed, where it is contiguous to the last described bone.—Behind, this bone is triangular, where it is articulated with the os naviculare; and it is also triangular at its fore-part, where it is contiguous to the os metatarsi of the toe next to the great one.

Os cuneiforme maximum, or internum, differs from the two former in its situation, which is more oblique than theirs.—Besides, its broad thick part is placed below, and the small thin point is above and outwards; while its under broad surface is concave, for allowing a safe passage to the flexors of the great toe.—The surface of this os cuneiforme behind, where it is joined to the os naviculare, is hollow, smooth, and of a circular figure below, but pointed above.—The external side consists of two smooth and flat surfaces, whose direction is nearly at right angles with each other. With the posterior, that runs obliquely from below forwards and upwards, the os cuneiforme minimum is joined; and with the anterior, whose direction is longitudinal, the os metatarsi of the toe next to the great one is connected.—The fore-part of this bone is semilunar, but flat and smooth, for sustaining the os metatarsi of the great toe.—The internal side is scabrous, with two remarkable tubercles below, from which the musculus abductor pollicis rises, and the tibialis anticus is inserted into its upper part.

The three cuneiform bones are all so secured by ligaments, that very little motion is allowed in any of them.

These seven bones of the tarus, when joined, are convex above, and leave a concavity below, for lodging safely the several muscles, tendons, vessels, and nerves that lie in the sole of the foot.—In the recent subject, their upper and lower surfaces are covered with strong ligaments, which adhere firmly to them; and all the bones are so tightly connected, by these and the other ligaments, which are fixed to the rough ridges and fossae formerly mentioned, that, notwithstanding the many surfaces covered with cartilage, some of which are of the form of the very moveable articulations, no more motion is here allowed, than only to prevent too great a shock of the fabric of the body in walking, leaping, &c. by falling on too solid a base.

Metatarsus is composed of five bones, which, in their general characters, agree with the metacarpal bones; but may be distinguished from them by the following marks: 1. They are longer, thicker, and stronger. 2. Their anterior round ends are not so broad, and are less in proportion to their bases. 3. Their bodies are sharper above and flatter on the sides, with their inferior ridge inclined more to the outside. 4. The tubercles at the lower parts of the round head are larger.

The first or internal metatarsal bone is easily distinguished from the rest by its thickness.—The one next to it is the longest, and with its sharp edge almost perpendicular.—The others are shorter and more oblique, as their situation is more external.

Os metatarsi pollicis is by far the thickest and strongest, as having much the greatest weight to sustain. Its base is oblong, irregularly concave, and of a semilunar figure, to be adapted to the os cuneiforme maximum.—The inferior edge of this base is a little prominent and rough, where the tendon of the peronaeus primus muscle is inserted.—On its outside, an oblique circular depression is made by the second metatarsal bone.—Its round head has generally on its fore-part a middle ridge, and two oblong cavities, for the os sesamoideum; and on the external side, a depression is made by the following bone.

Os metatarsi of the second toe, is the longest of the five, with a triangular base supported by the os cuneiforme medium and the external side produced into a process; the end of which is an oblique smooth plane, joined to the os cuneiforme externum.—Near the internal edge of the base, this bone has two small depressions, made by the os cuneiforme maximum, between which is a rough cavity.—Farther forwards, we may observe a smooth protuberance, which is joined to the foregoing bone.—On the outside of the base are two oblong smooth surfaces, for its articulation with the following bone; the superior smooth surface being extended longitudinally, and the inferior perpendicularly; between which there is a rough fossa.

Os metatarsi of the middle toe, is the second in length.—Its base, supported by the os cuneiforme externum, is triangular, but slanting outwards, where it ends in a sharp-pointed little process; and the angle below is not completed. The internal side of this base is adapted to the preceding bone; and the external side has also two smooth surfaces covered with cartilage, but of a different figure; for the upper one is concave, and, being round behind, turns smaller as it advances forwards; and the lower surface is little, smooth, convex, and very near the edge of the base.

Os metatarsi of the fourth toe, is near as long as the former, with a triangular slanting base, joined to the os cuboides, and made round at its external angle, having one hollow smooth surface on the outside, where it is pressed upon by the following bone, and two on the internal side, corresponding to the former bone; behind which is a long narrow surface impressed by the os cuneiforme externum.

Os metatarsi of the little toe, is the shortest, situated with its two flat sides above and below, and with the ridges laterally.—The base of it, part of which rests on the os cuboides, is very large, tuberous, and produced into a long-pointed process externally, where part of the abductor minimi digiti is fixed; and into its upper part the peronaeus secundus is inserted.—Its inside has a flat conoidal surface, where it is contiguous to the preceding bone.

When we stand, the fore-ends of these metatarsal bones, and the os calcis, are our only supporters; and therefore it is necessary they should be strong, and should have a confined motion.

The bones of the Toes are much akin to those of the thumb and fingers; particularly the two of the great toe are precisely formed as the two last of the thumb; only their position, in respect of the other toes, is not oblique; and they are proportionally much stronger, because they are subjected to a greater force; for they sustain the force with which our bodies are pushed forwards by the foot behind at every step we make; and on them principally the weight of the body is supported, when we are raised on our tiptoes.

The three bones in each of the other four toes, compared to those of the fingers, differ from them in these particulars.—They are less, and smaller in proportion to their lengths.—Their bases are much larger than their anterior ends; Their bodies are more narrow above and below, and flatter on the sides.—The first phalanx is proportionally much longer than the bones of the second and third, which are very short.

Of the four, the toe next to the great one has the largest bones in all dimensions, and more externally the toes are less.—The little toe, and frequently that next to it, have the second and third bones intimately united into one; which may be owing to little motion, and the great pressure they are subjected to.

The toes are of good use to us in walking; for, when the sole is raised, they bring our body, with its centre of gravity, perpendicular to the advanced foot.

The only bones now remaining to complete the description of the skeleton, are the small ones, which are found at the joints of the fingers and toes, and in some other parts, called

Ossa Sesamoidea, which are of very different figures and sizes, though they are generally said to resemble the seed of the fænum.—They seem to be nothing else than the ligaments of the articulations, or the firm tendons of strong muscles, or both, become bony, by the compression which they suffer. Thus the sesamoid bones at the beginning of the gastrocnemii muscles, are evidently composed of the tendinous fibres only.—These, at the first joint of the great toe, are as plainly the same continued substance with the ligaments and the tendons of the adductor, flexor, brevis, and abductor.—That which is sometimes double at the second joint of that toe, is part of the capsular ligament; and if we enumerate the other sesamoid bones that are at any time found, we may observe all of them formed in this manner.—Their number, figure, situation, and magnitude, are so uncertain, that it were in vain to insist on the differences of each; and therefore we shall only in general remark,

1. That wherever the tendons and ligaments are firmest, the actions of the muscles strongest, and the compression greatest, there such bones are most commonly found.

2. That, cæteris paribus, the older the subject is in which they are sought, their number is greater, and their size is larger.

3. The more labour any person is inured to, he has, cæteris paribus, the most numerous and largest offa sesamoidea.

EXPLANATION OF PLATE XIII.

Figure I. A Male Skeleton.

A, Os frontis. B, Os parietale. C, Os temporum. D, Os occipitis. E, Os nasi. F, Os maxillare superius. G, Os maxillare inferius. H, Os maxillare inferius. I, The teeth, which are sixteen in each jaw. K, The seven vertebrae of the neck, with their intermediate cartilages. L, &c. 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 tarso. l, The five metatarsal bones. m, The phalanges of the toes. Part I. ANATOMY.

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.

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, through which the spinal marrow passes. h, The foramen lingualis, 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 patroa. d, The zygomatic process. e, The styloid process. f, The entry of the auditory nerve.

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 spongium superius. c, The nasal lamella. d, The ethmoid cells. e, Crista galli.

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

Fig. 9. The side of the Os Unguis 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 Maxillae. 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 palatini. 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. 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 temporale and occipitis. H, The pars squamosa of the os temporale. 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 through 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 suture. D, The lambdoid suture. E, The squamous future. F, The furrows made by the vessels of the dura mater. G, The frontal sinus. H, The crista 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. F F, The two condyles. G, The cuneiform process. H H, The zygomatic process of the temporal bone. I I, The mastoid processes. K, The vomer, which forms the back-part of the septum nasi. L L, The styloid processes. M M, The fossa at the root of the mastoid processes, for the posterior belly of the digastric muscle. N N, The cavities for receiving the condyles of the lower jaw. O O, The osse palati. P, The longitudinal palate-suture. Q, The transverse palate-suture. R, The alveoli, or fangy sockets for the teeth. S, The zygomatic process of the osse malarum. T T, 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.

Explanation of 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 costal. e, Cervix. f, Glenoid cavity, covered with cartilage for the arm-bone. g 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 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 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 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 b, The parts of the extremity of the tibia, covered with cartilage, which appear within the semilunar cartilages. c 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 f, The two parts of the crucial ligaments. g g, The edges of the two moveable semilunar cartilages. h, The tibia. Part I.