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exterior warm pouch, formed of the skin; it hangs by the mouth, until, from being a minute and shapeless thing, it is matured to the degree when the offspring of other animals are usually brought forth.
Now it appears that the upright position of this animal, and the disproportioned magnitude of the lower part of its body— for it is the only creature except man which rests in the perpendicular-may account for the peculiarity of its mode of gestation. Without entering far into the subject, we may observe that an accurate correspondence must subsist between the form of the young offspring and the bones of the mother through which it has to be expelled. In animals generally, the head is the larger part; but in the kangaroo, that bears no proportion to the magnitude of the hind quarters; for when an animal is designed for the perpendicular position, the hip-bones must necessarily be of large size to sustain the weight; and such is the case with the kangaroo. Nature has, therefore, accomplished the production of the young safely, and by the simplest means,—that is, by anticipating the period of the separation of the young animal ; and providing for its growth exteriorly, after it has passed through the circle of bones called the pelvis. For these reasons we conclude that there is a relation between the mode of producing the offspring, and the form of the skeleton, in this animal.
I hope that I have now gone far enough to prove that where uniformity is preserved in the shape of any part of the skeleton, it depends on the permanence in the function of the organ. In certain respects the head and spine are persistent in their forms; but that is merely because the brain and spinal marrow contained within the skull and vertebral column do not vary, except in point of relative size. As regards the application of the bones of the face to be instruments for obtaining food, for attack, or defence, they are ever curiously changed in their processes and articulations, in accommodation to the numerous different modes of using the parts. In fine, we may observe, that there never takes place any modification in the form of the parts of the body, whether in the forehead, occiput, jaws, teeth, spine, pelvis, or extremities, without a corresponding adaptation extending through the whole skeleton.
IMAGINARY ANIMALS.-"No doubt we can imagine a greater variety of animals than do actually exist;" such are the words of Archdeacon Paley. But what is the fact? Suppose we take the fabled animals of antiquity; not one of them could have existed!
It may serve both to show the imperfection of man's ingenuity, compared with nature, and the perfection of the system of the animal body, if, for a moment, we examine these imaginary animals, and inquire whether they could have fed, or breathed, or moved, or flown.
What, in fact, are these monstrous fancies, but an incongruous union of parts of different animals, patched together without order or system, and which could not have belonged to any living creature? When the head of a lion is joined to the belly of a goat, or the head of a woman to the body of a bird, or the body of a man to the tail of a serpent, there is no real invention. Not one of the centaurs of Thessaly, satyrs of the Indian mountains, sphinxes of Egypt, griffins among the one-eyed nations, could have stood, run, or flown. It may be alleged, and perhaps truly, that these figures were mere allusive representations-the mystical types of some country or element. It is sufficient, however, for our argument, that such are the only imaginary animals which have been acquiesced in by the classical scholar, as having had a fanciful existence.
In the antique marble figure of the centaur, the merit of the sculptor is evinced by his success in reconciling our fancy to the unnatural union of the various members: for example, in the face, the expansion of the nostrils, and the coltish wildness of the expression, are in correct correspondence with the artist's design of joining to the human form that of the horse. But this attempt at combined representation would not have satisfied one narrowly acquainted with the proportions of the horse. He would know that too heavy a fore-quarter, too long a neck, or too large a head, was incompatible with wind, speed, or safe going; and he would have concluded that an animal with such defects would be unsound, would founder in the feet. What, then, would he have said to a centaur, where, besides head and extremities, an additional body is made to rest upon the fore-legs?
Galen wonders if Pindar believed in centaurs. "For," says he, "if such an animal were to exist, it ought to have two mouths; one to correspond to the stomach of man; the other
to masticate for the stomach of the horse. If it could run upon the plain, it could not climb the hill, or make its way in rocky places. Though possessed of human faculties, it could not build for itself an habitation, or navigate ships, or man the sails ;" and, more particular still in his objections, he adds, "that it could neither sit like the tailor, nor make shoes like the cobbler."
How nature manages to rear a heavy structure on the forelegs of a quadruped, without the incumbent weight bearing inordinately upon them, we saw when examining the skeleton of the giraffe. We observed that the pressure of the greatly elongated neck was partly taken off the fore-quarters, and directed on the hind-legs by the oblique position of the spine and shortness of the hind-quarters. However beautiful, then, as works of art, may be the figures of the centaur upon antique gems, they are yet monsters; their construction, a joining together of incongruous parts.
Few designs are more icult to execute than that of the fawn or satyr. This results from the artist having to reconcile the inconsistencies of a human form and face united to the limbs of a brute. If we have attended to the great size and strength of the human lower extremities, as compared with the upper part of the body, we may have perceived the incongruity of rearing the human trunk and head upon the hind-legs of a goat, the bones of which are disproportionately small, and the masses of muscle misplaced. This is not thought of by the painter and sculptor, when they represent their fawns dancing and piping. An instant's consideration of the comparative size and relative position of the bones, and of the action of the muscles, would have shown that the limbs must have been incapable of such activity. Had these fabulous forms actually existed, they must have crept weakly along the ground.
And so of the griffin. Eagle's wings could never have raised the body of the lion. For a creature to rise on the wing, there must be not only a mass of muscle proportioned to the extended wing, but a surface of bone of sufficient extent to give lodgment and attachment to the muscles of flight. Corresponding to the muscular strength of the lion, his bones are thick, dense, and heavy; now a skeleton composed of such bones would never answer for a creature that was to be buoyant in the air. Accordingly, even if the external forms were consistent, the internal conformation would be incompatible with the existence of
such an animal as the griffin. The lion's tail, again, would be a very useless appendage, compared with the fine rudder with which the eagle directs his swoop.
These instances might be multiplied. But we venture to say that every animal form, not actually existing in nature, but the invention of the artist or poet, would be discovered to have some defect in the balance of the exterior members, or in the relation of the parts necessary for motion; or were the exterior and moving parts duly balanced, some internal organ would be found unconformable, or displaced-too much developed, or too much compressed. In short, man's imagination is more limited than he may at first have believed. His inventions are only the incongruous union of things presented separately in nature. It is, indeed, far beyond his power to accomplish what was supposed possible by Paley, who said, "that multitudes of conformations, both of vegetables and animals, may be conceived capable of existence and succession, which yet do not exist."
This manner of viewing the subject confirms more strongly our belief in the perfection of that natural system of parts, which, in an infinite variety of creatures, admits of all the changes necessary for the different acts of walking, running, flying, swimming, &c.; at the same time that it accommodates the internal functions which minister to life, to every condition of existence to which the animal may be destined.
APPROPRIATE SENSIBILITIES INDUCE COMBINED MUSCU
LAR ACTIONS, FOR THE PROTECTION OF THE VITAL
In addition to the examples given in Chap. VII., we offer one or two more, to show how the sensibilities, which are endowments of life, vary and are adapted to the mechanical organisation, with an appropriation more admirable than the mechanism. The sensibility we allude to differs from that of the skin. It is put in connection with numerous muscles; and without its high and peculiar property of controlling, independently of the will, the multiplied combinations of the muscles, the mechanical provisions we are about to describe would be useless.
The top of the windpipe, the larynx, consists of five elastic cartilages. These do not merely keep the sides of the windpipe apart, and a passage for the breath free, but they perform offices important to the economy both of body and mind; they are an essential part of the instrument of voice: they at the same time guard the lungs from injury.
The thyroid cartilage is the largest; it is that which we feel projecting on the fore part of the throat. Situated behind, and within the embrace of the thyroid, are the arytenoid cartilages, of an irregularly triangular form, socketed on the cricoid cartilage below, and perfectly moveable. Between the corners of the arytenoid cartilages, which project forwards, and the thyroid, are stretched, from behind forwards, two ligaments, parallel, and at a little distance from each other, called the vocal cords (corda vocales); these ligaments or cords, being invested with the lining membrane of the windpipe, a slit, like the till of a shop-counter, is formed between them; and through this chink (called rima glottidis) the air passes to and fro. To the sides and back part of the arytenoid cartilages small muscles are attached; and these, by moving the cartilages, tighten or relax the cordæ vocales; which, again, by vibrating in the stream of air, vocalise the breath, and the tones so produced are articulated in speech.