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at the wrist, which implies claws. But claws may belong to two species of animals: to the feline, which possess sharp carnivorous teeth; or to animals without either canine or cutting teeth, the edentata. If he should also find the lower extremity of the same bone, and observe on its surface spines and grooves, the marks of tendons, which, instead of running straight to be inserted into a single bone, radiated to distinct phalanges,—he would conclude that there must have been moveable claws, that the bone must have belonged to a carnivorous animal; and he would seek for canine teeth of corresponding size.
THE LAST DIVISION OF THE BONES OF THE ARM.
In the human hand, the bones of the wrist (carpus) are eight in number; and they are so closely connected that they form a sort of ball, which moves on the end of the radius. Beyond these, and towards the fingers, forming the palm of the hand, are the five metacarpal bones, which diverge at their further extremities, and give support to the bones of the thumb and fingers. In the thumb, the first phalangeal bone is absent. There are thus in the hand twenty-seven bones; from the mechanism of which result strength, mobility, and elasticity.
Lovers of system do not use the term disparagingly) delight to trace the gradual subtraction of the bones of the hand. Thus, looking to the hand of man, they see the thumb fully formed. In the monkeys (simiæ) they find it exceedingly small; in one of them, the spider-monkey (see page 13), it has almost disappeared, and the four fingers are sufficient, with hardly the rudiments of a thumb. In some of the tardigrade animals, as we have seen (in page 20), there are only three metacarpal bones, with three fingers. In the ox, the cannon-bone consists of two coalesced metacarpal bones, and the double hoofs are supported by the corresponding phalangeal bones. In the horse, the cannon-bone is a single metacarpal bone, and the great pastern, little pastern, and coffin or hoof bone, represent a single finger.* Indeed, we might go further and instance the wing of the bird. To me, this appears to be losing the sense, in the love of system; there is no regular gradation, but, as I have often to repeat, a variety, which most curiously adapts the same system of parts to every necessary purpose.
* See Owen on the Nature of Limbs, p. 32. -(S.)
In a comparative view of these bones, we are led more particularly to take notice of the foot of the horse. It is universally admitted to be of beautiful design, and calculated for strength and elasticity, and especially provided against concussion.
The bones of the fore-leg of the horse become firmer as we trace them downwards. The two bones corresponding to those of the fore-arm, are braced together and consolidated; and the motion at the elbow-joint is limited to flexion and extension. The carpus, forming what by a sort of licence is called the knee, is also newly modelled; but the metacarpal bones and phalanges of the fingers are totally changed, and can hardly be recognised. When we look in front, instead of the four metacarpal bones, we see one strong bone, the cannon-bone; and posterior to this, we find two lesser bones, called splint-bones.
The heads of these lesser or splint-bones enter into the kneejoint (or properly the wrist-joint); at their lower ends they diminish gradually, and they are held by an elastic ligamentous attachment to the sides of the cannon-bone. I have some hesitation in admitting the correctness of the opinion held by veterinary surgeons, on this curious piece of mechanism; they imagine that these moveable splint-bones, by playing up and down as the foot is alternately raised and pressed to the ground, bestow elasticity and prevent concussion. The fact certainly is that by over action, the parts become inflamed, and these bones are eventually united to the greater metacarpal or cannonbone; and that this, which is called a splint, is a cause of lameness. I suspect, rather, that in the perfect. state of the joint, these lesser metacarpal or splint-bones act as a spring, to assist in throwing out the foot, when the knee-joint is bent, and the
Bones of Horse's Fore-leg.
extensor muscles begin to act. If we admit that it is on the quickness of extension of the joint that the rate of motion must principally depend, it will not escape observation, that in the bent position of the knee, the extensor tendons, from running near the centre of motion, have very little power; and that, in fact, they require some additional means to aid the extension of the leg. Suppose the head of the splint-bone (A) enters into the composition of the joint, it does not appear that when the leg is straight and the foot on the ground, the bones of the carpus, sustained as they are by the cannon-bone, can descend and press upon it, so as to bring its elasticity into action. But, in the bent position of the knee, the head of the splint-bone will come in contact with the carpal bones, behind the centre of motion of the joint; and it is obvious, therefore, that, when the foot is elevated and the knee bent, the splint bone will be depressed, in opposition to its elastic connecting ligament; so that, as soon as the action of the flexor muscles ceases, it will recoil, and thereby assist the extensor muscles in throwing out the leg into the straight position. Further, we can readily believe that when the elasticity of these splint-bones is lost, by ossification uniting them firmly to the cannon-bone, the want of such a piece of mechanism, essential to the quick extension of the foot, will cause lameness, and make the horse apt to come down.
The mechanism of the bones and tendons of the extremities is infinitely varied; and we hardly ever discern anything uncommon in the outward configuration of an animal, but we find something new The gait, or rather strut, of the ostrich is peculiar; and it results from a very singular
Hock-joint of the Ostrich.
and appropriate in the anatomy.
mechanism, a spring joint, at the part corresponding with the hock.*
OF THE HORSE'S FOOT.-On looking to the sketch (page 59), and comparing it with that of the bones of the hand (page 55), we see that in the horse's fore-leg, five bones of the first digital row are represented by the large pastern-bone; those of the second by the lesser pastern, or coronet; and those of the last by the coffin-bone.
For illustrating the general subject of our treatise, nothing is better suited than the horse's foot: it is a most perfect piece of mechanism. And whilst examining it, we are impressed with the peculiarity of living mechanism,-that it can be preserved perfect only by the natural exercise of its parts. The horse, originally a native of extensive plains and steppes, has a structure admirably conformed to these his natural pasture-grounds. But when brought into subjection, to run on hard roads, the foot suffers from concussion. His value, so often impaired by lameness, has made the structure of the horse's foot an object of great interest; and I have it from the excellent professor of veterinary surgery to say, that he has never demonstrated the anatomy of this part without perceiving something new to admire.
The weight and power of the animal require that both strength and elasticity should be combined in his foot. Hence the first thing that attracts attention is the position of the bones. Had they been placed one directly over the other,
* The figures (p. 60) illustrate the structure referred to. There is a gentle rising of the bone at A, having a smooth lubricated surface, and a groove in front and behind. In the straight position, the lateral ligament B is lodged in the deep groove at the back of the tubercle; but as the leg is bent, the ligament glides upon the tubercle, it becomes more and more stretched till it reaches the highest point of the convexity, and then it slips, with a jerk, into the shallower groove in front as the leg is extended, the ligament is again stretched on passing over the tubercle, and falls back, with another jerk, into the groove
behind. This play of the ligament over the tubercle, as over a doubleinclined plane, is accompanied, at each sliding movement, with a sudden start of the joint, both in flexion and extension; and it is that which gives rise to the peculiar strut of the animal. The object of the structure seems to be to knit or support the joint, when the bird is resting on the limb; and also, in flexion of the joint, to facilitate that great projection of the superior bone backwards, as seen in fig. 2, by which additional power is given to the muscle C, that propels the bird in its course. See Chapter IV.
there could not have been elasticity; accordingly, they are disposed obliquely, and a strong elastic ligament runs behind, terminating by an attachment to the lowest or coffin-bone. So essential is the obliquity of the bones to the elasticity of the limb, that without mounting a horse, it is possible, by observing the direction of the pastern and coffin-bones, to say whether he goes easily or not.*
The bones of the foot of the camel rest on a soft elastic cushion. In the horse's foot, there is a structure of a similar kind, but it acts very differently, and never comes to the ground; nor, indeed, does the sole of the horse's foot directly bear the weight. The horny frog, the triangular projection in the hollow of the hoof, has placed above it an elastic frog or cushion; and inasmuch as these parts receive the weight of the animal, and by their descent, when the foot is on the ground, press out the crust or horny hoof, they are essential to the structure of the foot. The anterior tip of this crust, or the part of the hoof which last touches the ground as the foot rises, is very dense and firm, to withstand the pressure and impulse forward the lateral parts, however, are elastic, and on their play depends that resiliency of the foot which prevents concussion. The crust is not consolidated with the bone called coffin-bone; certain elastic laminæ, growing from the bone and dovetailed into the crust, are interposed between them. When the animal puts his foot to the ground, the weight bears on the coffin-bone, and from its being attached to the circle of the crust by these elastic laminæ, the lateral parts yield, and the weight is directed on the margins of the crust; the sole never touching the ground, unless it has become diseased.
Xenophon, speaking of the Persian horses, says that their grooms were careful to curry them on a pavement of round stones, that by beating their feet against a firm and irregular surface, the texture of the foot might be put into exercise. It corresponds curiously with this, that our high-bred horses are
*The arched form of the bones, at the fetlock, with their convexity backwards, and the distinctness of the elastic ligament and tendons behind the cannon-bone, can be perceived by the eye and the hand, and constitute one of the "points" of a
horse. Such is the correspondence between the strength of an animal's bones, tendons, and muscles, that from these sinews the jockey can infer the perfection or defect of the whole.