watch (I mean the chain which passes between | no account can be given from the structure or the spring-barrel and the fusee,) which aims at exercise of the part. the same properties, is but a bungling piece of workmanship in comparison with that of which we speak. IV. The reciprocal enlargement and contraction of the chest to allow for the play of the lungs, depends upon a simple yet beautiful mechanical contrivance, referable to the structure of the bones which enclose it. The ribs are articulated to the back-bone, or rather to its side projections, obliquely: that is, in their natural position they bend or slope from the place of articulation downwards. But the basis upon which they rest at this end being fixed, the consequence of the obliquity, or the inclination downwards, is, that when they come to move, whatever pulls the ribs upwards, necessarily, at the same time, draws them out; and, that, whilst the ribs are brought to a right angle with the spine behind, the sternum, or part of the chest to which they are attached in front, is thrust forward. The simple action, therefore, of the elevating muscles does the business: whereas, if the ribs had been articulated with the bodies of the vertebræ at right angles, the cavity of the thorax could never have been farther enlarged by a change of their position. If each rib had been a rigid bone, articulated at both ends to fixed bases, the whole chest had been immoveable. Keill has observed, that the breast-bone, in an easy inspiration, is thrust out one tenth of an inch: and he calculates that this, added to what is gained to the space 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. When 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 of 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 * Anat. p. 229. 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 shoulder-blade 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 hyoides:) 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 arms, 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. 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 cabinetmaker'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 have 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 tention. the binding up of a fracture, where the fillet is al most 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 dislo cation, 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 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 The suppleness and pliability of the joints, we stronger on the sides than either before or behind, every moment experience; and the firmness of in order that the convexities may play true in animal articulation, the property we have hitherto their concavities, and not be subject to slip side- been considering, may be judged of from this sinways, which is the chief danger; for the muscu-gle observation, that, at any given moment of lar 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 II. The joints, or rather the ends of the bones cross each other; and cross each other in such a which form them, display also, in their configuramanner, as to secure the joint from being dis- tion, another use. The nerves, blood-vessels, and placed in any assignable direction. "I think," tendons, which are necessary to the life, or for the says Cheselden," that the knee cannot be com- motion, of the limbs, must, it is evident, in their pletely dislocated without breaking the cross liga-way from the trunk of the body to the place of ments." We can hardly help comparing this with *Ches. Anat. ed. 7th. p. 45. 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. their destination, travel over the moveable joints; and it is no less 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 comprehension, 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 cubital 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 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 blood-vessels steal to their destination in the arm, instead of mounting over the edge of the concavity.t 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 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 over-rate 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. Ches. Anat. p. 255. ed. 7. †Th. p. 30. † Ib. p. 35. § Ib. p. 13. The cartilages 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 is 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 of 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.) 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, 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 ducts of which glands, dripping with their balsamic contents, hang loose like fringes within 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. 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 exercised as the joints are. This durability I should attribute, in part, to the provision which is made for the preventing of wear and tear, first, by the polish of the cartilagi nous surfaces; secondly, by the healing lubrication of the mucilage; and, in part, to that astonishing property of animal constitutions, assimilation, by which, in every portion of the body, let it consist of what it will, substance is restored, and waste repaired. Moveable joints, I think, compose the curiosity of bones; but their union, even where no motion is intended or wanted, carries marks of mechanism and of mechanical wisdom. The teeth, espe cially the front teeth, are one bone fixed in another, like a peg driven into a board. The sutures of the skull are like the edges of two saws clapped together, in such a manner as that the teeth of one enter the intervals of the other. We have sometimes one bone lapping over another, and planed down at the edges: sometimes also the thin lamella of one bone received into a narrow furrow of another. In all which varieties, we seem to discover the same design, viz. firmness of juncture, without clumsiness in the seam. 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. great defect in the articulation: for the joint in the neck, although admirably adapted to the motion of the head, is insufficient for its support. It is not only by the means of a most curious structure of the bones that a man turns his head, but by virtue of an adjusted muscular power, that he even holds it up. As another example of what we are illustrating, viz. conformity of use between the bones and the muscles, it has been observed of the different vertebræ, that their processes are exactly proportioned to the quantity of motion which the other bones allow of, and which the respective muscles are capable of producing. II. A muscle acts only by contraction. Its force is exerted in no other way. When the exertion ceases, it relaxes itself, that is, it returns by relaxation to its former state, but without energy. I. We may observe, what I believe is universal, This is the nature of the muscular fibre; and an exact relation between the joint and the mus- being so, it is evident that the reciprocal energetic cles which move it. Whatever motion the joint, motion of the limbs, by which we mean motion by its mechanical construction, is capable of per- with force in opposite directions, can only be proforming, that motion, the annexed muscles, by duced by the instrumentality of opposite or antatheir position, are capable of producing. For ex-gonist muscles; of flexors and extensors answering ample; if there be, as at the knee and elbow, a to each other. For instance, the biceps and brahinge-joint, capable of motion only in the same chiæus internus muscles placed in the front part plane, the leaders, as they are called, i. e. the of the upper arm, by their contraction, bend the muscular tendons, are placed in directions parallel elbow; and with such degree of force, as the to the bone, so as, by the contraction or relaxation case requires, or the strength admits of. The reof the muscles to which they belong, to produce laxation of these muscles, after the effort, would that motion and no other. If these joints were merely let the fore-arm drop down. For the back capable of a freer motion, there are no muscles to stroke, therefore, and that the arm may not only produce it. Whereas at the shoulder and the hip, bend at the elbow, but also extend and straighten where the ball and socket-joint allows by its con- itself, with force, other muscles, the longus and struction of a rotatory or sweeping motion, ten- brevis brachiæus externus and the anconæus, dons are placed in such a position, and pull in placed on the hinder part of the arms, by their consuch a direction, as to produce the motion of which tractile twitch fetch back the fore-arm into a the joint admits. For instance, the sartorius or straight line with the cubit, with no less force tailor's muscle, rising from the spine, running di- than that with which it was bent out of it. The agonally across the thigh, and taking hold of the same thing obtains in all the limbs, and in every inside of the main bone of the leg, a little below moveable part of the body. A finger is not bent the knee, enables us, by its contraction, to throw and straightened, without the contraction of two one leg and thigh over the other; giving effect, muscles taking place. It is evident, therefore, that at the same time, to the ball and socket-joint at the animal functions require that particular dispothe hip, and the hinge-joint at the knee. There sition of the muscles which we describe by the is, as we have seen, a specific mechanism in the name of antagonist muscles. And they are acbones, for the rotatory motions of the head and cordingly so disposed. Every muscle is provided hands: there is, also, in the oblique direction of with an adversary. They act, like two sawyers the muscles belonging to them, a specific provision in a pit, by an opposite pull and nothing surely for the putting of this mechanism of the bones can more strongly indicate design and attention into action. And mark the consent of uses. The to an end, than their being thus stationed, than oblique muscles would have been inefficient with- this collocation. The nature of the muscular fibre out that particular articulation: that particular being what it is, the purposes of the animal could articulation would have been lost, without the ob- be answered by no other. And not only the calique muscles. It may be proper however to ob-pacity for motion, but the aspect and symmetry of serve, with respect to the head, although I think the body, is preserved by the muscles being marit does not vary the case, that its oblique motions shalled according to this order; e. g. the mouth is and inclinations are often motions in a diagonal, holden in the middle of the face, and its angles produced by the joint action of muscles lying in kept in a state of exact correspondency, by two straight directions. But whether the pull be sin-muscles drawing against, and balancing each other. gle or combined, the articulation is always such, In a hemiplegia, when the muscle on one side is as to be capable of obeying the action of the mus- weakened, the muscle on the other side draws the cles. The oblique muscles attached to the head, mouth awry. are likewise so disposed, as to be capable of steadying the globe, as well as of moving it. The head of a new-born infant is often obliged to be filleted up. After death, the head drops and rolls in every direction. So that it is by the equilibre of the muscles, by the aid of a considerable and equipollent muscular force in constant exertion, that the head maintains its erect posture. The muscles here supply what would otherwise be a III. Another property of the muscles, which could only be the result of care, is, their being almost universally so disposed, as not to obstruct or interfere with one another's action. I know but one instance in which this impediment is perceived. We cannot easily swallow whilst we gape. This, I understand, is owing to the muscles employed in the act of deglutition being so implicated with the muscles of the lower jaw, that, whilst these last are contracted, the former cannot act with freedom. The obstruction is, in this instance, attended with little inconveniency; but it shows what the effect is where it does exist; and what loss of faculty there would be if it were more frequent. Now when we reflect upon the number of muscles, not fewer than four hundred and forty-six in the human body, known and named, how contiguous they lie to each other, in layers, as it were, over one another, crossing one another, sometimes imbedded in one another, sometimes perforating one another; an arrangement, which leaves to each its liberty, and its full play, must necessarily require meditation and counsel. repeated-How many things not right for us to be ar hour at ease! how many more for us to be vigorous and active! Yet vigour and activity are, in a vast plurality of instances, preserved in human bodies, notwithstanding that they depend upon so great a number of instruments of motion, and notwithstanding that the defect or disorder sometimes of a very small instrument, of a single pair, for instance, out of the four hundred and forty-six muscles which are employed, may be attended with grievous inconveniency. There is piety and good sense in the following observation, taken out of the Religious Philosopher: "With much compassion," says this writer, "as well as astonishment at the goodness of our loving Creator, have I considered the sad state of a certain gentleman, who, as to the rest, was in pretty good health, but only wanted the use of these two little muscles that serve to lift up the eyelids, and so had almost lost the use of his sight, being forced, as long as this defect lasted, to shove up his eyelids every moment with his own hands!"-In general we may remark in how small a degree those, who enjoy the perfect use of their organs, know the comprehensiveness of the blessing, the variety of their obligation. They perceive a result, but they think little of the multitude of concurrences and rectitudes which go to form it. IV. The following is oftentimes the case with the muscles. Their action is wanted, where their situation would be inconvenient. In which case, the body of the muscle is placed in some commodious position at a distance, and made to communicate with the point of action, by slender strings or wires. If the muscles which move the fingers had been placed in the palm or back of the hand, they would have swelled that part to an awkward and clumsy thickness. The beauty, the proportions of the part, would have been destroyed. They are therefore disposed in the arm, and even up to the elbow; and act by long tendons, strapped down at the wrist, and passing under the ligaments to the fingers, and to the joints of the fingers, which they are severally to move. In like man-muscular organ as such, we may notice some adner, the muscles which move the toes, and many vantages of structure which are more conspicuous of the joints of the foot, how gracefully are they in muscles of a certain class or description than disposed in the calf of the leg, instead of forming in others. Thus: an unwieldy tumefaction in the foot itself? The observation may be repeated of the muscle which draws the nictitating membrane over the eye; its office is in the front of the eye; but its body is lodged in the back part of the globe, where it lies safe, and where it encumbers nothing. Beside these observations, which belong to the I. The variety, quickness, and precision, of which muscular motion is capable, are seen, I think, in no part so remarkably as in the tongue. It is worth any man's while to watch the agility of his tongue; the wonderful promptitude with which it executes changes of position, and the V. The great mechanical variety of the figure perfect exactness. Each syllable of articulated of the muscles may be thus stated. It appears to sound requires for its utterance a specific action be a fixed law, that the contraction of a muscle of the tongue and of the parts adjacent to it. The shall be towards its centre. Therefore the subject disposition and configuration of the mouth, apperfor mechanism on each occasion is, so to modify taining to every letter and word, is not only pecuthe figure, and adjust the position of the muscle, liar, but, if nicely and accurately attended to, peras to produce the motion required, agreeably with ceptible to the sight; in so much, that curious this law. This can only be done by giving to persons have availed themselves of this circumdifferent muscles a diversity of configuration, stance to teach the deaf to speak, and to undersuited to their several offices, and to their situation stand what is said by others. In the same person, with respect to the work which they have to per- and after his habit of speaking is formed, one, and form. On which account we find them under a only one, position of the parts, will produce a multiplicity of forms and attitudes; sometimes given articulate sound correctly. How instantawith double, sometimes with treble tendons, some-neously are these positions assumed and dismisstimes with none: sometimes one tendon to seve- ed; how numerous are the permutations, how ral muscles, at other times one muscle to several various, yet how infallible! Arbitrary and antic tendons. The shape of the organ is susceptible variety is not the thing we admire; but variety of an incalculable variety, whilst the original pro- obeying a rule, conducing to an effect, and comperty of the muscle, the law and line of its con-mensurate with exigencies infinitely diversified. I traction, remains the same, and is simple. Herein the muscular system may be said to bear a perfect resemblance to our works of art. An artist does not alter the native quality of his materials, or their laws of action. He takes these as he finds them. His skill and ingenuity are employed in turning them, such as they are, to his account, by giving to the parts of his machine a form and relation, in which these unalterable properties may operate to the production of the effects intended. VI. The ejaculations can never too often be *Keill's Anatomy, p. 295. ed. 3. believe also that the anatomy of the tongue corresponds with these observations upon its activity. The muscles of the tongue are so numerous, and so implicated with one another, that they cannot be traced by the nicest dissection; nevertheless, (which is a great perfection of the organ,) neither the number, nor the complexity, nor what might seem to be the entanglement of its fibres, in any wise impede its motion, or render the determination or success of its efforts uncertain. I HERE entreat the reader's permission to step a little out of my way, to consider the parts of the |