within the chest by the flattening or descent of the diaphragm, leaves room for forty-two cubic inches of air to enter at every drawing-in of the breath. Where there is a necessity for a deeper and more laborious inspiration, the enlargement of the capacity of the chest may be so increased by effort, as that the lungs may be distended with seventy or a hundred such cubic inches *. The thorax, says Schelhammer, forms a kind of bellows, such as never have been, nor probably will be, made by any artificer.

V. The patella, or knee-pan, is a curious little bone; in its form and office, unlike any other bone in the body. It is circular; the size of a crown-piece; pretty thick; a little convex on both sides, and covered with a smooth cartilage. It lies upon the front of the knee; and the powerful tendons, by which the leg is brought forward, pass through it (or rather it makes a part of their continuation), from their origin in the thigh to their insertion in the tibia. It protects both the tendon and the joint from any injury which either might suffer, by the rubbing of one against the other, or by the pressure of unequal surfaces. It also gives to the tendons a very considerable mechanical advantage, by altering the line of their direction, and by advancing it farther out from the centre of motion; and this upon the principles of the resolution of force, upon which principles all machinery is founded. These are its uses. But what is most observable in it is, that it appears to be supplemental, as it were, to the frame; added, as it should almost seem, afterward; not quite necessary, but very convenient. It is separate from the other bones; that is, it is not connected with any other bones by the common mode of union. It is soft, or hardly formed, in infancy; and produced by an ossification, of the inception or progress of which no account can be given from the structure or exercise of the part.

VI. The shoulder-blade is, in some material respects, a very singular bone; appearing to be made so expressly for its own purpose, and so independently of every other reason. In such quadrupeds as have no collar-bones, which are by far the greater number, the shoulderblade has no bony communication with the trunk, either by a joint, or process, or in any other way. It does not grow to, or out of, any other bone of the trunk. It does not apply to any other bone of the trunk (I know not whether this be true of any second bone in the body, except perhaps the os hyoïdes): in strictness, it forms no part of the skeleton. It is bedded in the flesh; attached only to the muscles. It is no other than a foundation bone for the arm, laid in, separate as it were, and distinct, from the general ossification. The lower limbs connect themselves at the hip with bones which form part of the skeleton: but this connexion, in the upper limbs, being wanting, a basis, whereupon the arm might be articulated, was to be supplied by a detached ossification for the purpose†.

* Anat. p. 229. Bones differ exceedingly in their texture, yet they are upon all occasions adapted to the circumstances in which they are placed; the structure always corresponds to the purposes for which they are employed. The ribs of newly-born creatures are the only bones that are hard, for these only at that period have occasion for a superior degree of strength. All the other bones are mere cartilage, yielding to the pressure attendant upon parturition, and affording security against the falls and accidents to which all young creatures are liable. The bones of the fore-foot of a race-horse and of a deer are unusually hard, though small qualities necessary to be combined to sustain the force with which they strike the ground when the animal is at its full speed, and yet to offer no unnecessary extent of surface to the opposing air. The hardness of these bones is scarcely equal to that of the lion's foreleg, his great weapon of attack and defence. This is so remarkable that it was thought to have a peculiar chemical composition; but Mr. Hatchett has shown this to be not the case. It only contains a greater proportion of phosphate of lime than other bones; its strength arises chiefly from superior compactness of structure.

When the bones are enlarged for the purposes of strength, or to give attachment to muscles, the contrivances are most perfect. Galileo, on strict mathematical

principles, has shown, that when solid bodies are increased in dimensions, the destroying power proceeds in a quadru plicate proportion, while the preserving power rises only in a triplicate ratio. The all-wise Creator provided against this law by making all large bones hollow, and thus at the same time removed the centre of motion to the greatest practicable distance from the centre of gravity, giving the utmost possible strength that can be obtained from the given quantity of materials.

Bones which have neither weight to support nor great resistance to make are formed proportionably slight; but then they are light because hollow.

Independently of this variation in the structure of bones, fitting them for their several offices, they are also adapted to the medium in which the animal lives. The bones of all aquatic animals are of small specific gravity. This is provided in various modes. Cartilaginous fishes have very little phosphate of lime in their bones. In the whale tribe, as the bones must be strong as well as have an extended surface, their internal cavities are filled with oil. The enormous head of the spermaceti whale has its blowholes kept above the surface of the water, by means of a peculiar large cavity filled with spermaceti, which is so much specifically lighter than water.-Sir Everard Home's Lectures on Comparative Anatomy.

The bones connected with the ear are among the hard

OF THE JOINTS.

I. THE above are a few examples of bones made remarkable by their configuration: but to almost all the bones belong joints; and in these, still more clearly than in the form or shape of the bones themselves, are seen both contrivance and contriving wisdom. Every joint is a curiosity, and is also strictly mechanical. There is the hinge-joint and the mortice and tenon-joint; each as manifestly such, and as accurately defined, as any which can be produced out of a cabinet-maker's shop; and one or the other prevails, as either is adapted

to the motion which is wanted: e. g. a mortice and tenon, or ball and socket joint, is not required at the knee, the leg standing in need only of a motion backward and forward in the same plane, for which a hinge-joint is sufficient; a mortice and tenon, or ball and socket joint, is wanted at the hip, that not only the progressive step may be provided for, but the interval between the limbs may be enlarged or contracted at pleasure. Now observe what would have been the inconveniency, i. e. both the superfluity and the defect of articulation, if the case had been inverted: if the ball and socket joint had been at the knee, and the hinge-joint at the hip. The thighs must have been kept constantly together, and the legs had been loose and straddling. There would have been no use, that we know of, in being able to turn the calves of the legs before; and there would have been great confinement by restraining the motion of the thighs to one plane. The disadvantage would not have been less, if the joints at the hip and the knee had been both of the same sort; both balls and sockets, or both hinges: yet why, independently of utility, and of a Creator who consulted that utility, should the same bone (the thigh-bone) be rounded at one end, and channelled at the other?

The hinge-joint is not formed by a bolt passing through the two parts of the hinge, and thus keeping them in their places; but by a different expedient. A strong, tough, parchment-like membrane, rising from the receiving bones, and inserted all round the received bones a little below their heads, encloses the joint on every side. This membrane ties, confines, and holds, the ends of the bones together; keeping the corresponding parts of the joint, i. e. the relative convexities and concavities, in close application to each other.

For the ball and socket joint, besides the membrane already described, there is in some important joints, as an additional security, a short, strong, yet flexible ligament, inserted by one end into the head of the ball, by the other into the bottom of the cup; which ligament keeps the two parts of the joint so firmly in their place, that none of the motions which the limb naturally performs, none of the jerks and twists to which it is ordinarily liable, nothing less indeed than the utmost and the most unnatural violence, can pull them asunder. It is hardly imaginable, how great a force is necessary, even to stretch, still more to break, this ligament: yet so flexible is it, as to oppose no impediment to the suppleness of the joint. By its situation also, it is inaccessible to injury from sharp edges. As it cannot be ruptured (such is its strength); so it cannot be cut, except by an accident which would sever the limb. If I had been permitted to frame a proof of contrivance, such as might satisfy the most distrustful inquirer, I know not whether I could have chosen an example of mechanism more unequivocal, or more free from objection, than this ligament. Nothing can be more mechanical; nothing, however subservient to the safety, less capable of being generated by the action of the joint. I would particularly solicit the reader's attention to this provision, as it is found in the head of the thigh-bone; to its strength, its structure, and its use. It is an instance upon which I lay my hand. One single fact, weighed by a mind in earnest, leaves oftentimes the deepest impression. For the purpose of addressing different understandings and different apprehensions,-for the purpose of sentiment, for the purpose of exciting admiration of the Creator's works, we diversify our views, we multiply examples; but for the purpose of strict argument, one clear instance is sufficient; and not only suffi

sally as it ought for, as it is well observed by Sir Charles Bell, in his Bridgewater Treatise," there is inconsistency and something of the child's propensities still in mankind." "A piece of mechanism, as a watch, a barometer, or a dial, will fix attention: a man will make journeys to see an engine stamp a coin, or turn a block; yet the organs through which he has a thousand sources of enjoy ment, and which are in themselves more exquisite in design, and more curious both in contrivance and in mechanism, do not enter his thoughts; and if he admire a living action, that admiration will probably be more excited, by what is uncommon and monstrous, than by what is natural and perfectly adjusted to its office, by the elephant's trunk than by the human hand. It is the effect of habit. The human hand is so beautifully formed, it has so fine a sensibility, that sensibility governs its

motions so correctly, every effort of the will is answered so instantly, as if the hand itself were the seat of that will; its actions are so powerful, so free, and yet so delicate, that it seems to possess a quality instinct in itself, and there is no thought of its complexity as an instrument, or of the relations which make it subservient to the mind; we use it as we draw our breath, unconsciously, and have lost all recollection of the feeble and ill-directed efforts of its first exercise, by which it has been perfected."-Bell on the Hand, p. 12; Pepys-Nicholson, vol. xiii., p. 216; Geh. Jour., vol. iii., p. 1; vol. vi., p. 591; Hatchett, Phil. Trans. 1799, p. 328; Fourcroy and Vauquelin Memoirs, Institute, vol. ii., p. 284; Ann. Phil. vol. ix., p. 55; Dr. Thomson, vol. iv., p. 461; Davy, Agri. Chem., p. 291; Sir E. Home's Lectures on Comparative Anatomy.

cient, but capable perhaps of generating a firmer assurance than what can arise from a divided attention.

The ginglymus, or hinge-joint, does not, it is manifest, admit of a ligament of the same kind with that of the ball and socket joint, but it is always fortified by the species of ligament of which it does admit. The strong, firm, investing membrane, above described, accompanies it in every part: and in particular joints, this membrane, which is properly a ligament, is considerably stronger on the sides than either before or behind, in order that the convexities may play true in their concavities, and not be subject to slip sideways, which is the chief danger; for the muscular tendons generally restrain the parts from going farther than they ought to go in the plane of their motion. In the knee, which is a joint of this form, and of great importance, there are superadded to the common provisions for the stability of the joint, two strong ligaments which cross each other and cross each other in such a manner, as to secure the joint from being placed in any assignable direction. "I think," says Cheselden, "that the knee cannot be completely dislocated without breaking the cross ligaments*." We can hardly help comparing this with the binding up of a fracture, where the fillet is almost always strapped across, for the sake of giving firmness and strength to the bandage.

:

Another no less important joint, and that also of the ginglymus sort, is the ankle; yet though important (in order, perhaps, to preserve the symmetry and lightness of the limb), small, and, on that account, more liable to injury. Now this joint is strengthened, i. e. is defended from dislocation, by two remarkable processes or prolongations of the bones of the leg, which processes form the protuberances that we call the inner and outer ankle. It is part of each bone going down lower than the other part, and thereby overlapping the joint: so that, if the joint be in danger of slipping outward, it is curbed by the inner projection, i. e. that of the tibia; if inward, by the outer projection, i. e. that of the fibula. Between both, it is locked in its position. I know no account that can be given of this structure, except its utility. Why should the tibia terminate, at its lower extremity, with a double end, and the fibula the same,-but to barricade the joint on both sides by a continuation of part of the thickest of the bone over it? The joint at the shoulder, compared with the joint at the hip, though both ball and socket joints, discovers a difference in their form and proportions, well suited to the different offices which the limbs have to execute. The cup or socket at the shoulder is much shallower and flatter than it is at the hip, and is also in part formed of cartilage set round the rim of the cup. The socket, into which the head of the thigh-bone is inserted, is deeper, and made of more solid materials. This agrees with the duties assigned to each part. The arm is an instrument of motion, principally, if not solely. Accordingly the shallowness of the socket at the shoulder, and the yieldingness of the cartilaginous substance with which its edge is set round, and which in fact composes a considerable part of its concavity, are excellently adapted for the allowance of a free motion and a wide range; both which the arm wants. Whereas, the lower limb, forming a part of the column of the body; having to support the body, as well as to be the means of its locomotion; firmness was to be consulted, as well as action. With a capacity for motion, in all directions indeed, as at the shoulder, but not in any direction to the same extent as in the arm, was to be united stability, or resistance to dislocation. Hence the deeper excavation of the socket; and the presence of a less proportion of cartilage upon the edge.

The suppleness and pliability of the joints, we every moment experience; and the firmness of animal articulation, the property we have hitherto been considering, may be judged of from this single observation, that, at any given moment of time, there are millions of animal joints in complete repair and use, for one that is dislocated; and this, notwithstanding the contortions and wrenches to which the limbs of animals are continually subject.

II. The joints, or rather the ends of the bones which form them, display also, in their configuration, another use. The nerves, blood-vessels, and tendons, which are necessary to the life, or for the motion, of the limbs, must, it is evident, in their way from the trunk of the body to the place of their destination, travel over the moveable joints; and it is no less

* Cheselden's Anatomy, ed. 7th, p. 45.

evident, that, in this part of their course, they will have, from sudden motions, and from abrupt changes of curvature, to encounter the danger of compression, attrition, or laceration. To guard fibres so tender against consequences so injurious, their path is in those parts protected with peculiar care; and that by a provision, in the figure of the bones themselves. The nerves which supply the fore-arm, especially the inferior cubical nerves, are at the elbow conducted, by a kind of covered way, between the condyls, or rather under the inner extuberances of the bone, which composes the upper part of the arm*. At the knee, the extremity of the thigh-bone is divided by a sinus or cliff into two heads or protuberances and these heads on the back part stand out beyond the cylinder of the bone. Through the hollow, which lies between the hind-parts of these two heads, that is to say, under the ham, between the ham-strings, and within the concave recess of the bone formed by the extuberances on each side; in a word, along a defile, between rocks, pass the great vessels and nerves which go to the leg. Who led these vessels by a road so defended and secured? In the joint at the shoulder, in the edge of the cup which receives the head of the bone, is a notch, which is joined or covered at the top with a ligament. Through this hole, thus guarded, the bloodvessels steal to their destination in the arm, instead of mounting over the edge of the concavity‡.

III. In all joints, the ends of the bones which work against each other, are tipped with gristle. In the ball and socket joint, the cup is lined, and the ball capped with it. The smooth surface, the elastic and unfriable nature of cartilage, render it of all substances the most proper for the place and purpose. I should, therefore, have pointed this out amongst the foremost of the provisions which have been made in the joints for the facilitating of their action, had it not been alleged, that cartilage in truth is only nascent or imperfect bone; and that the bone in these places is kept soft and imperfect, in consequence of a more complete and rigid ossification being prevented from taking place by the continual motion and rubbing of the surfaces; which being so, what we represent as a designed advantage, is an unavoidable effect. I am far from being convinced that this is a true account of the fact; or that, if it were so, it answers the argument. To me, the surmounting of the ends of the bones with gristle, looks more like a plating with a different metal, than like the same metal kept in a different state by the action to which it is exposed. At all events, we have a great particular benefit, though arising from a general constitution: but this last not being quite what my argument requires, lest I should seem by applying the instance to overrate its value, I have thought it fair to state the question which attends it.

IV. In some joints, very particularly in the knees, there are loose cartilages or gristles between the bones, and within the joint, so that the ends of the bones, instead of working upon one another, work upon the intermediate cartilages. Cheselden has observed §, that the contrivance of a loose ring is practised by mechanics, where the friction of the joints of any of their machines is great; as between the parts of crook-hinges of large gates, or under the head of the male screw of large vices. The cartilages of which we speak, have very much of the form of these rings. The comparison moreover shews the reason why we find them in the knees rather than in other joints. It it an expedient, we have seen, which a mechanic resorts to, only when some strong and heavy work is to be done. So here the thigh-bone has to achieve its motion at the knee, with the whole weight of the body pressing upon it, and often, as in rising from our seat, with the whole weight of the body to lift. It should seem also, from Cheselden's account, that the slipping and sliding of the loose cartilages, though it be probably a small and obscure change, humoured the motion at the end of the thigh-bone, under the particular configuration which was necessary to be given to it for the commodious action of the tendons; (and which configuration requires what he calls a variable socket, that is, a concavity, the lines of which assume a different curvature in different inclinations of the bones)||.

Cheselden's Anatomy, p. 255, ed. 7.

+ Ibid. p. 35.

Ibid. p. 30.

§ Ibid. 13.

Paley has been charged with taking Cheselden and Keill for his authorities in anatomy, in preference to more

modern professors; but those who consider this as a crime, have been very slow in adducing any instances where these two great anatomists have led him into error. The talented Keill was the earlier writer of the two, and his work, "The Anatomy of the Human Body," was long the vade mecum of the medical student.

He