this subject farther, there are three views un- of an inch: and he calculates that this, added der which the spine ought to be regarded, and to what is gained to the space within the chest in all which, it cannot fail to excite our admi- by the flattening or descent of the diaphragm, ration. These views relate to its articulations, leaves room for forty-two cubic inches of air its ligaments, and its perforation; and to the to enter at every drawing-in of the breath. corresponding advantages which the body de- When there is a necessity for a deeper and rives from it, for action, for strength, and for more laborious inspiration, the enlargement that which is essential to every part, a secure of the capacity of the chest may be so increas communication with the brain. ed 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.

The structure of the spine is not in general different in different animals. In the serpent tribe, however, it is considerably varied; but with a strict reference to the conveniency of the animal. For, whereas in quadrupeds the V. The patella, or knee-pan, is a curious number of vertebræ is from thirty to forty, in little bone; in its form and office, unlike any the serpent it is nearly one hundred and fif- other bone of the body. It is circular; the ty: whereas in men and quadrupeds the sur- size of a crown piece; pretty thick; a little faces of the bones are flat, and these flat sur- convex on both sides, and covered with a faces laid one against the other, and bound smooth cartilage. It lies upon the front of the tight by sinews; in the serpent, the bones knee: and the powerful tendons, by which the play one within another like a ball and soc-leg is brought forward, pass through it (or raket, so that they have a free motion upon ther it makes a part of their continuation,) one another in every direction: that is to say, from their origin in the thigh to their inser in men and quadrupeds, firmness is more con- tion in the tibia. It protects both the tendon sulted; in serpents, pliancy. Yet even pli- and the joint from any injury which either ancy is not obtained at the expense of safety. might suffer, by the rubbing of one against The back-bone of a serpent, for coherence and the other, or by the pressure of unequal surflexibility, is one of the most curious pieces of faces. It also gives to the tendons a very conanimal mechanism with which we are ac-siderable mechanical advantage, by altering quainted. The chain of a watch (I mean the the line of their direction, and by advancing chain which passes between the spring-barrel it farther out from the centre of motion; and and the fusee,) which aims at the same properties, is but a bungling piece of workmanship in comparison with that of which we speak.

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 IV. The reciprocal enlargement and con- supplemental, as it were, to the frame: addtraction of the chest to allow for the play of ed, as it should almost seem, afterward; not the lungs, depends upon a simple yet beauti- quite necessary, but very convenient. It is ful mechanical contrivance, referable to the separate from the other bones; that is, it is structure of the bones which enclose it. The not connected with any other bones by the ribs are articulated to the back-bone, or ra- common mode of union. It is soft, or hardther to its side projections, obliquely: that is, ly formed, in infancy; and produced by an in their natural position they bend or slope ossification, of the inception or progress from the place of articulation downwards. But which no account can be given from the structhe basis upon which they rest at this end be- ture or exercise of the part. ing fixed, the consequence of the obliquity, or VI. The shoulder-blade is, in some material the inclination downwards, is, that when they respects, a very singular bone; appearing to come to move, whatever pulls the ribs up-be made so expressly for its own purpose, and wards, necessarily, at the same time, draws so independently of every other reason. In them out; and that, whilst the ribs are brought such quadrupeds as have no collar-bones, which to a right angle with the spine behind, the are by far the greater number, the shouldersternum, or part of the chest to which they blade has no bony communication with the are attached in front, is thrust forward. The trunk, either by a joint, or process, or in any simple action, therefore, of the elevating mus- other way. It does not grow to, or out of, cles does the business; whereas, if the ribs had any other bone of the trunk. It does not apbeen articulated with the bodies of the verte-ply to any other bone of the trunk: (I know bræ at right angles, the cavity of the thorax not whether this be true of any second bone could never have been farther enlarged by a in the body, except perhaps the os hyoïdes :) change of their position. If each rib had been in strictness, it forms no part of the skeleton. a ridged bone, articulated at both ends to fix- It is bedded in the flesh; attached only to the ed bases, the whole chest had been immove-muscles. It is no other than a foundation able. Keill has observed, that the breast-bone, bone for the arm, laid in, separate, as it were, in an easy inspiration, is thrust ont one-tenth and distinct, from the general ossification. The

Der. Phys. Theol. p. 396.

* Anat. p. 229.

Lower limbs connect themseives at the hip with short, strong, yet flexible ligament, inserted bones which form part of the skeleton; but by one end into the head of the ball, by the this connexion, in the upper limbs, being want- other into the bottom of the cup; which ligaing, a basis, whereupon the arm might be ar-ment keeps the two parts of the joint so firmticulated, was to be supplied by a detatched ossification for the purpose.

OF THE JOINTS.

ly 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 1. The above are a few examples of bones asunder. It is hardly imaginable, how great made remarkable by their configuration: but a force is necessary, even to stretch, still more to almost all the bones belong joints; and in to break, this ligament; yet so flexible is it, as these, still more clearly than in the form or to oppose no impediment to the suppleness of shape of the bones themselves, are seen both the joint. By its situation also, it is inaccescontrivance and contriving wisdom. Every sible to injury from sharp edges. As it canjoint is a curiosity, and is also strictly mecha- not be ruptured (such is its strength ;) so it nical. There is the hinge-joint and the mor- cannot be cut, except by an accident which tice and tenon-joint; each as manifestly such, would sever the limb. If I had been permitand as accurately defined, as any which can be ted to frame a proof of contrivance, such as produced out of a cabinet-maker's shop; and might satisfy the most distrustful inquirer, I one or the other prevails, as either is adapted know not whether I could have chosen an exto the motion which is wanted: e. g. a mor- ample of mechanism more unequivocal, or tice and tenon, or ball and socket-joint, is not more free from objection, than this ligament. required at the knee, the leg standing in need Nothing can be more mechanical; nothing, only of a motion backward and forward in the however subservient to the safety, less capasame plane, for which a hinge-joint is suffi- ble of being generated by the action of the cient; a mortice and tenon, or ball and soc-joint. I would particularly solicit the reader's ket-joint, is wanted at the hip, that not only attention to this provision, as it is found in the progressive step may be provided for, but the head of the thigh-bone; to its strength, its the interval between the limbs may be enlarg-structure, and its use. It is an instance upon ed or contracted at pleasure. Now observe which I lay my hand. One single fact, weighwhat would have been the inconveniency, i. e.ed by a mind in earnest, leaves oftentimes the both the superfluity and the defect of articu- deepest impression. For the purpose of adlation, if the case had been inverted; if the dressing different understandings and differball and socket-joint had been at the knee, and ent appprehensions,-for the purpose of senthe hinge-joint at the hip. The thighs must timent, for the purpose of exciting admiration have been kept constantly together, and the of the Creator's works, we diversify our views, legs had been loose and straddling. There we multiply our examples; but for the purwould have been no use, that we know of, in pose of strict argument, one clear instance is being able to turn the calves of the legs be-sufficient; and not only sufficient, but capafore; and there would have been great con- ble perhaps of generating a firmer assurance finement 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:

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, The hinge-joint is not formed by a bolt pas- is considerably stronger on the sides than eising through the two parts of the hinge, and ther before or behind, in order that the conthus keeping them in their places; but by a vexities may play true in their concavities, different expedient. A strong, tough, parch- and not be subject to slip sideways, which is ment-like membrane, rising from the receiv- the chief danger; for the muscular tendons ing bones, and inserted all round the received generally restrain the parts from going farbones a little below their heads, encloses the ther than they ought to go in the plane of joint on every side. This membrane ties, con- their motion. In the knee, which is a joint fines, and holds the ends of the bones toge- of this form, and of great importance, there ther; keeping the corresponding parts of the joint, i. c. the relative convexities and concavities, in close application to each other.

are superadded to the common provisions for the stability of the joint, two strong ligaments which cross each other; and cross each other For the ball and socket-joint, beside the mem-in such a manner, as to secure the joint from brane already described, there is in some im- being displaced in any assignable direction. portant joints, as an additional security, a" I think," says Cheselden, "that the knee

cannot be completely dislocated without break-ed of from this single observation, that, at any ing the cross ligaments.' ." We can hardly help given moment of time, there are millions of comparing this with the binding up of a frac- animal joints in complete repair and use, for ture, where the fillet is almost always strap-one that is dislocated; and this, notwithstandped across, for the sake of giving firmness and ing the contortions and wrenches to which strength to the bandage. the limbs of animals are continually subject. Another no less important joint, and that II. The joints, or rather the ends of the also of the ginglymus sort, is the ankle; yet bones which form them, display also, in their though important (in order, perhaps, to pre- configuration, another use. The nerves, bloodserve the symmetry and lightness of the limb,) vessels, and tendons, which are necessary to small, and, on that account, more liable to in- the life, or for the motion of the limbs, must, jury. Now this joint is strengthened, i. e. is it is evident, in their way from the trunk of defended from dislocation, by two remarkable the body to the place of their destination, traprocesses or prolongations of the bones of the vel over the moveable joints; and it is no less leg, which processes, form the protuberances evident, that, in this part of their course, they that we call the inner and outer ankle. It is will have, from sudden motions, and from part of each bone going down lower than the abrupt changes of curvature, to encounter the other part, and thereby overlapping the joint: danger of compression, attrition, or laceration. so that, if the joint be in danger of slipping To guard fibres so tender against consequences outward, it is curbed by the inner projection, so injurious, their path is in those parts proi. e. that of the tibia; if inward, by the out-tected with peculiar care; and that by a provier projection, i. e. that of the fibula. Be- sion in the figure of the bones themselves. The tween both, it is locked in its position. I know nerves which supply the fore-arm, especially no account that can be given of this structure, the inferior cubical nerves, are at the elbow' except its utility. Why should the tibia ter- conducted, by a kind of covered way, between minate, at its lower extremity, with a double the condyls, or rather under the inner extuend, and the fibula the same, but to barricade berances of the bone, which composes the upthe joint on both sides by a continuation of per part the arm. At the knee, the extremipart of the thickest of the bone over it? The ty of the thigh-bone is divided by a sinus or joint at the shoulder, compared with the joint cliff into two heads or protuberances: and at the hip, though both ball and socket joints, these heads on the back part stand out beyond discovers a difference in their form and pro- the cylinder of the bone. Through the holportions, well suited to the different offices low, which lies between the hind parts of these which the limbs have to execute. The cup or two heads, that is to say, under the ham, besocket at the shoulder is much shallower and tween the ham-strings, and within the concave flatter than it is at the hip, and is also in part recess of the bone formed by the extuberances formed of cartilage set round the rim of the on each side; in a word, along a defile, between cup. The socket, into which the head of the rocks, pass the great vessels and nerves which thigh-bone is inserted, is deeper, and made of go to the leg. Who led these vessels by a more solid materials. This agrees with the road so defended and secured? In the joint duties assigned to each part. The arm is an at the shoulder, in the edge of the cup which instrument of motion, principally, if not solely. receives the head of the bone, is a notch, which Accordingly the shallowness of the socket at is joined or covered at the top with a ligament. the shoulder, and the yieldingness of the car-Through this hole, thus guarded, the bloodtilaginous substance with which its edge is set vessels steal to their destination in the arm, round, and which in fact composes a consider- instead of mounting over the edge of the conable part of its concavity, are excellently ad- cavity. apted for the allowance of a free motion and III. In all joints, the ends of the bones, a wide range; both which the arm wants. which work against each other, are tipped with Whereas, the lower limb, forming a part of the gristle. In the ball and socket joint, the cup column of the body; having to support the is lined, and the ball capped with it. The body, as well as to be the means of its locomo- smooth surface, the elastic and unfriable nation; firmness was to be consulted, as well as ture of cartilage, render it, of all substances, action. With a capacity for motion, in all the most proper for the place and purpose. I directions indeed, as at the shoulder, but not should, therefore, have pointed this out amongst in any direction to the same extent as in the the foremost of the provisions which have been arm, was to be united stability, or resistance made in the joints for the facilitating of their to dislocation. Hence the deeper excavation action, had it not been alledged, that cartilage of the socket; and the presence of a less pro-in truth is only nascent or imperfect bone; portion of cartilage upon the edge. and that the bone in these places is kept soft

The suppleness and pliability of the joints, and imperfect, in consequence of a more com. we every moment experience; and the firm.plete and rigid ossification being prevented ness of animal articulation, the property we from taking place by the continual motion and have hitherto been considering may be judg

* Ches. Anat. ed. 7th. p. 45.

Ches. Anat. p. 255, ed. 7. 1 lb. p. 30.

+ lb. p. 35.

the cavity of the joints. A late improvement in what are called friction-wheels, which consist of a mechanism so ordered, as to be regularly dropping oil into a box, which encloses the axis, the nave, and certain balls upon which the nave revolves, may be said, in some sort, to represent the contrivance in the animal joint, with this superiority, however, on the part of the joint, viz. that here, the oil is not only dropped, but made.

rubbing of the surfaces; which being so, what | ducts of which glands, dripping with their balwe represent as a designed advantage, is an samic contents, hang loose like fringes within 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.

In considering the joints, there is nothing, perhaps, which ought to move our gratitude more than the reflection, how well they wear. A limb shall swing upon its hinge, or play in its socket, many hundred times in an hour, for sixty years together, without diminution of its agility: which is a long time for any thing to last; for any thing so much worked and ex

should attribute, in part, to the provision which is made for preventing of wear and tear; first, by the polish of the cartilaginous surfaces; secondly, by the healing lubrication of the mucilage; and, in part, to that astonishing pro

which, in every portion of the body, let it consist of what it will, substance is restored, and waste repaired.

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 upone another, work upon the intermediate car-ercised as the joints are. This durability, I tilages. Cheselden has observed, that the contrivance of a loose ring is practised by mechanics, where the friction of the joints 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 carti-perty of animal constitutions, assimilation, by lages of which we speak, have very much of the form of these rings. The comparison, moreover, shows the reason why we find them in the knees rather than in other joints. It Moveable joints, I think, compose the cuis an expedient, we have seen, which a me- riosity of bones; but their union, even where chanic resorts to, only when some strong and no motion is intended or wanted, carries marks heavy work is to be done. So here the thigh- of mechanism and of mechanical wisdom. The bone has to achieve its motion at the knee, teeth, especially the front teeth, are one bone with the whole weight of the body pressing fixed in another, like a peg driven into a board. upon it, and often, as in rising from our seat, The sutures of the skull are like the edges of with the whole weight of the body to lift. It two saws clapped together, in such a manner should seem also, from Cheselden's account, as that the teeth of one enter the intervals of that the slipping and sliding of the loose car-the other. We have sometimes one bone laptilages, though it be probably a small and ob-ping over another, and planed down at the scure change, humoured the motion at the end edges; sometimes also the thin lamella of one of the thigh bone, under the particular confi-bone received into a narrow furrow of another. guration which was necessary to be given to In all which varieties, we seem to discover the it for the commodious action of the tendons; same design, viz. firmness of juncture, with(and which configuration requires, what he out clumsiness in the seam. calls, a variable socket, that is, a concavity, the lines of which assume a different curvature in different inclinations of the bones.)

V. We have now done with the configuration but there is also in the joints, and that common to them all, another exquisite provision, manifestly adapted to their use, and concerning which there can, I think, be no dispute, namely, the regular supply of a mucilage, more emollient and slippery than oil itself, which is constantly softening and lubricating the parts that rub upon each other, and thereby diminishing the effect of attrition in the highest possible degree. For the continual secretion of this important liniment, and for the feeding of the cavities of the joint with it, glands are fixed near each joint; the excretory

Ches. Anat. p. 13, ed. 7.

CHAPTER IX.

OF THE MUSCLES.

MUSCLES, with their tendons, are the instruments by which animal motion is performed. It will be our business to point out instances in which, and properties with respect to which, the disposition of these muscles is as strictly mechanical, as that of the wires and strings of a puppet.

I. We may observe, what I believe is universal, an exact relation between the joint and the muscles which move it. Whatever motion the joint, by its mechanical construction, is capable of performing, that motion, the annexed

muscles, by their position, are capable of pro- which the other bones allow of, and which the ducing. For example; if there be, as at the respective muscles are capable of producing knee and elbow, a hinge-joint, capable of mo- II. A muscle acts only by contraction. Its tion only in the same plane, the leaders, as they force is exerted in no other way. When the are called, i. e. the muscular tendons, are plac- exertion ceases, it relaxes itself, that is, it reed in directions parallel to the bone, so as, by turns by relaxation to its former state; but the contraction or relaxation of the muscles to without energy. This is the nature of the mus which they belong, to produce that motion and cular fibre: and being so, it is evident that the no other. If these joints were capable of a reciprocal energetic motion of the limbs, by freer motion, there are no muscles to produce which we mean motion with force in opposite it. Whereas at the shoulder and the hip, directions, can only be produced by the instru where the ball and socket joint allows by its mentality of opposite or antagonist muscles; construction of a rotatory or sweeping motion, of flexors and extensors answering to each o tendons are placed in such a position, and pull ther. For instance, the biceps and brachiaus in such a direction, as to produce the motion internus muscles, placed in the front part of of which the joint admits. For instance, the the upper arm, by their contraction, bend the sartorius or tailor's muscle, rising from the elbow; and with such degree of force, as the spine, running diagonally across the thigh, and case requires, or the strength admits of. The taking hold of the inside of the main bone of relaxation of these muscles, after the effort, the leg, a little below the knee, enables us, by would merely let the fore-arm drop down. For its contraction, to throw one leg and thigh over the back stroke, therefore, and that the arm the other; giving effect, at the same time, to may not only bend at the elbow, but also exthe ball and socket joint at the hip, and the tend and straighten itself with force, other hinge-joint at the knee. There is, as we have muscles, the longus and brevis brachiæus erseen, a specific mechanism in the bones, for the ternus and the anconæus, placed on the hinder rotatory motions of the head and hands: there part of the arms, by their contractile twitch is, also, in the oblique direction of the muscles fetch back the forearm into a straight line belonging to them, a specific provision for the with the cubit, with no less force than that putting of this mechanism of the bones into ac-with which it was bent out of it. The same tion. And mark the consent of uses, the ob- thing obtains in all the limbs, and in every lique muscles would have been inefficient with- moveable part of the body. A finger is not out that particular articulation: that particu-bent and straightened, without the contraction lar articulation would have been lost, without of two muscles taking place. It is evident the oblique muscles. It may be proper how-therefore, that the animal functions require ever to observe with respect to the head, al- that particular disposition of the muscles which though I think it does not vary the case, that we describe by the name of antagonist muscles. its oblique motions and inclinations are often And they are accordingly so disposed. Every motions in a diagonal, produced by the joint muscle is provided with an adversary. They action of muscles lying in straight directions. act, like two sawyers in a pit, by an opposite But whether the pull be single or combined, pull: and nothing surely can more strongly the articulation is always such, as to be capable indicate design and attention to an end, than of obeying the action of the muscles. The ob- their being thus stationed, than this collocation. lique muscles attached to the head, are likewise The nature of the muscular fibre being what so disposed, as to be capable of steadying the it is, the purposes of the animal could be anglobe, as well as of moving it. The head of a swered by no other. And not only the capa. new-born infant is often obliged to be filleted city for motion, but the aspect and symmetry up. After death the head drops and rolls in of the body is preserved by the muscles being every direction. So that it is by the equilibre marshalled according to this order, e. g. the of the muscles, by the aid of a considerable and mouth is holden in the middle of the face, and equipollent muscular force in constant exertion, its angles kept in a state of exact correspond that the head maintains its erect posture. The ency, by two muscles drawing against, and bamuscles here supply what would otherwise be lancing each other. In a hemiplegia, when a great defect in the articulation: for the joint the muscle on one side is weakened, the mus in the neck, although adinirably adapted to the cle on the other side draws the mouth awry. motion of the head, is insufficient for its sup-. III. Another property of the muscles, which port. It is not only by the means of a most could only be the result of care, is, their being curious structure of the bones that a man turns almost universally so disposed, as not to ob his head, but by virtue of an adjusted muscu- struct or interfere with one another's action. lar power, that he even holds it up. I know but one instance in which this impe

As another example of what we are illustrat-diment is perceived. We cannot easily swal ing, viz. conformity of use between the bones low whilst we gape. This, I understand, is and the muscles, it has been observed of the owing to the muscles employed in the act of different vertebræ, that their processes are ex- deglutition being so implicated with the mus actly proportioned to the quantity of motion cles of the lower jaw, that whilst these last are