are permanent in their offices; whilst the extremities vary and are adapted to every exterior circumstance. The office of the back part of the skull is to protect the brain, that of the spine to contain the spinal marrow, and the ribs to perform respiration. Why should we expect these parts to vary in shape while their office remains the same? But the shoulder must vary in form, as it does in motion. The shape of the bones and the joints of the extremities must be adapted to their various actions, and the carpus and phalanges must change, more than all the rest, to accommodate the extremity to its different offices. Is it not more pleasing to see the reason of this most surprising adjustment, than merely to say it is a law?

There is yet another opinion, which will suggest itself by the perusal of the following chapter, to those who have read the more modern works on Natural History. It is supposed that the same elementary parts belong to all animals, and that the varieties of structure are attributable to the transposition and moulding of these elementary parts. I find it utterly impossible to follow up this system to the extent which its abettors would persuade us to be practicable. I object to it as a means of engaging us in very trifling pursuits, and of diverting the mind from the truth; from that conclusion, indeed, to which I may avow it to be my intention to carry the reader. But this discussion also must follow the examples, and we shall resume it in a latter part of the volume.

CHAPTER III.

THE COMPARATIVE ANATOMY OF THE HAND.

In this inquiry, we have before us what in the strictest sense of the word is a system. All the individuals of the extensive division of the animal kingdom which we have to review, possess a cranium for the protection of the brain,-a heart, implying a peculiar circulation,-five distinguishable organs of sense; but the grand peculiarity, whence the term vertebrata is derived, is to be found in the spine; that chain of bones which connects the head and body, and, like a keel, serves as a foundation for the ribs; or as the basis of that fabric which is for respiration.

I have said, that we are to confine ourselves to a portion only of this combined structure; to separate and examine the anterior extremity, and to observe the adaptation of its parts, through the whole range of these animals. We shall view it as it exists in man, and in the higher division of animals which give suck, the mammalia-in those which propagate by eggs, the oviparous animals,

birds, reptiles, amphibia, and fishes; and we shall find the bones which are identified by distinct features, adjusted to various purposes, in all the series, from the arm to the fin. We shall recognise them in the mole, formed into a powerful apparatus for digging, by which the animal soon covers itself, and burrows its way under ground. In the wing of the eagle we shall count every bone adapted to a new element, and as powerful to rise in the air, as the fin of the salmon is to strike through the water. The solid hoof of the horse, the cleft foot of the ruminant, the retractile claw of the feline tribe, the long folding nails of the sloth, are among the many changes that are found in the adjustment of the chain of bones which, in man, ministers to the compound motions of the hand.

OF THE SHOULDER.

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Were it my purpose to teach the elements of this subject, I should commence with examining the lowest animals, and trace the bones of the anterior extremity as they come to resemble the human arm, and to be employed for a greater variety of uses in the higher animals; but as my present object is illustration only. I shall begin with the human hand, and compare its parts. With this view, I shall divide the extremity into the shoulder, arm, and hand, and treat each subdivision with a reference to its structure in animals.

In viewing the human figure, or human skeleton, in connexion with our present subject, we remark the strength and solidity of the lower extremities, in contrast with the superior. Not only are the lower limbs longer and larger than those of any other animal, but the pelvis is wider, and the obliquity of the neck of the thigh-bone greater. The distances of the larger processes on the upper ends of the thigh-bones (the trochanters,) from the sockets are also greater than in any of the vertebrata. Altogether the strength of these bones, the size and prominence of their processes, the great mass of the muscles of the loins and hips, distinguish man from every other animal; they secure to him the upright posture, and give him the perfect freedom of the arms, for purposes of ingenuity and art.

The Chimpanzee* is an ape which stands high in the order of quadrumana, yet we cannot mistake his capacities: that the lower extremities and pelvis, or hips, were never intended to give him the erect posture, or only for a moment; but, for swinging, or for a vigorous pull, who can deny him power in those long and sinewy

arms.

The full prominent shoulders, and the consequent squareness of the trunk, are equally distinctive of man, with the strength of his loins; they indicate a free motion of the hand.

OF THE BONES OF THE SHOULDER.

The bones of the shoulder, being those which give firm attachment to the upper extremity, and which afford origins to the muscles of the arm and fore arm, are simple, if studied in man, or, indeed, in any one genus of animals; but considered in reference

Simia troglodytes, from the coast of Guinea, more human in its form, and more easily domesticated than the ourang-outang. We would do well to consider the abode of these creatures in a state of nature--vast forests extending in impene trable shade below, whilst above, and exposed to the light, there is a scene of verdure and beauty; this is the home of those monkeys and lemurs which have extremities like hands. In many of them the hinder extremity has the more perfect resemblance to a hand; in the Goaita we see the great toe assuming the characters of a thumb, whilst in the fore paw, the thumb is not distinguishable, being hid in the skin. In short, these paws are not approximations to the hand, corresponding with a higher ingenuity, but are adaptations of the feet to the branches on which the animals climb.

to the whole of the vertebral animals, they assume a very extraordinary degree of intricacy. We shall, however, find that they retain their proper office, notwithstanding the strange variations in the form of the neighbouring parts. In man they are directly connected with the great apparatus of respiration; but in other animals we shall see the ribs, as it were, withdrawn from them, and the bones of the shoulder, or fundamental bones of the extremity, curiously and mechanically adapted to perform their office, without the support of the thorax. We shall not, however, anticipate the difficulties of this subject, but look first upon that which is most familiar and easy, the shoulder of man in comparison with the varieties in the mammalia.

The clavicle, or collar bone, is that which runs across from the breast bone to the top of the shoulder. The square form of the chest, and the free exercise of the hand, are very much owing to this bone. It keeps the shoulders apart from the chest, and throws the action of the muscles upon the arm bone, which, but for it, would be drawn inwards, and contract the upper part of the trunk.

If we take the motions of the anterior extremity in different animals, as our guide, we shall see why this bone is perfect in some, and entirely wanting in others. Animals which fly, or dig, or

climb, as bats, moles, porcupines, squirrels, ant-eaters, armadilloes, and sloths, have this bone, for in them, a lateral or outward motion is required. There is also a certain degree of freedom in the anterior extremity of the cat, dog, martin, and bear; they strike with the paw, and rotate the wrist more or less extensively, and they have therefore a clavicle, though an imperfect one. In some of these, even in the lion, the bone which has the place of the clavicle is very imperfect indeed; and if attached to the shoulder, it does not extend to the sternum; it is concealed in the flesh, and is like

A. Triangular portion of the Sternum. B. B. Clavicles. c. c. Scapula. D. Coracoid process of the Scapula. E. Acromion process of the Scapula.

the mere rudiments of the bone. But, however imperfect, it marks a correspondence in the bones of the shoulder to those of the arm and paw, and the extent of motion enjoyed.

When the bear stands up, we perceive, by his ungainly attitude and the motion of his paws, that there must be a wide difference in the bones of his upper extremity, from those of the ruminant or solipede. He can take the keeper's hat from his head, and hold it; he can hug an animal to death. The ant-bear especially, as he is deficient in teeth, possesses extraordinary powers of hugging with his great paws; and, although harmless in disposition, he can squeeze his enemy, the jaguar, to death. These actions, and the power of climbing, result from the structure of the shoulder, or from possessing a collar bone, however imperfect.

Although the clavicle is perfect in man, thereby corresponding with the extent and freedom of the motion of his hand, it is strongest and longest, comparatively, in the animals which dig or fly, as in the mole and the bat.

Preposterous as the forms of the kangaroo appear to us, yet even in this animal we see a relation preserved between the extremities. He sits upon his strong hind legs and tail, tripod like, with perfect security, and his fore paws are free. He has a clavicle, and possessing that bone and the corresponding motions, is not without means of defence; for with the anterior extremities he seizes the most powerful dog, and then drawing up his hinder feet, he digs his sharp pointed hoofs into his enemy, and striking out, tears him to pieces. Though possessed of no great speed, and without horns, teeth, or claws, and, as we should suppose, totally defenceless, nature has not been negligent of his protection.*

• There is in the form of the kangaroo, and especially in its skeleton, something incongruous, and in contrast with the usual shape of quadrupeds. The head, trunk, and fore paws, appear to be a portion of an animal, unnaturally joined to another of greater dimensions and strength. It is not easy to say what are, or what were, the exterior relations corresponding with the very peculiar form of this animal; but the interior anatomy is accommodated, in a most remarkable manner, to the enormous hinder extremities.

The uterine system of the female is diminutive, and does not undergo the developement, which universally takes place in other animals. The young, instead of remaining within the mother for the period of gestation, become, by some extraordinary mode of expulsion, attached to the teats; where they hang by the mouth, covered by an exterior pouch, until, from minute and shapeless things, they are matured to the degree in which the young of other animals are usually produced. The artery which supplies the milk glands, is the epigastric, a branch of the great artery of the thigh; and in this curious manner is the provision for the young drawn from the great limbs of the mother,-certainly the part best enabled to supply it.

I think I perceive the reason of this very peculiar manner of bringing forth the young, to be in the form of the animal and its upright position. The argument would stand thus, were we here at liberty to discuss it: 1. An upright position of the mother requires a pelvis of a peculiar and complex construction. 2. A pelvis, of this construction, requires that the form of the offspring shall accurately correspond, and that the anterior part of the fœtus shall much exceed in size the posterior parts.