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We thus see how Nature completes her work when the animal is destined to rise buoyant and powerful in the air :-the whole texture of the frame is altered, and made light in a manner consistent with strength; the mechanism of the anterior extremity is changed, and the muscles of the trunk are differently directed. But we are tempted to examine other instances, where the means, we would almost say, are more awkwardly suited for their purpose; that is, where the system of bones and muscles peculiar to the quadruped being preserved, the animal has still the power of launching into the air. We have already noticed how the structure of the bat is adapted to flight; but there are other animals, differing from birds more widely than it, which enjoy the function, though in a lesser degree. For example, the flying squirrel (Pteromys volucella), being chased to the end of a bough, spreads out the mantle which reaches along both its sides from the anterior to the posterior extremity, and drops in the air; and during its descent, it is met by such a resistance of the air from its extended skin and bushy tail, that it can direct its flight obliquely, and even turn, without any adaptation of the anterior extremity. Among reptiles, a provision of the same kind exists in the Draco fimbriatus; which, after creeping to a height, can drop safely to the ground, under the protection of a sort of parachute, formed by its extended skin. This is no inapt illustration: it is not the bones of the fingers that are here used to extend the web; but the ribs, which are unnecessary, in this animal, for breathing, are prolonged in a remarkable manner, like the whalebones of an umbrella, and upon them the skin is expanded.

This brings us to a very curious subject,-the condition of some of those Saurian reptiles, the remains of which are found only in a fossil state, most abundantly in the lias and oolite, termed the ancient strata of the Jura. The Pterodactyle of Cuvier is an animal which seems to confound all our notions of system. A lizard, yet its mouth was like the long bill of a bird, and its flexible neck corresponded; but it had teeth in its jaws like those of a crocodile. The bones of the anterior extremity were elongated, and fashioned somewhat like those in the wing

a contrary direction, and that the the wind may have arisen from that idea of migrating birds flying against mistake,

of a bird; but it could not have had feathers, as it had not a proper bill; we see no creature with feathers that has not a bill with which to dress and preen them. Nor did the extremity resemble that of a bat in structure: instead of the rows of bones being equally prolonged in all the fingers, as in the bat, the second finger only was extended to an extraordinary length ; whilst the third, fourth, and fifth had the size and articulations of those of a quadruped, and were terminated with sharp nails corresponding to the pointed teeth. The extended bones reached to double the whole length of the animal, and the conjecture is, that a membrane, resembling that of the Draco fimbriatus, was expanded upon them. In the imperfect specimens upon which we have to found our reasoning, we cannot discover, either in the height of the hip-bones, the strength of the vertebræ of the back, or the expansion of the breast-bone, a provision for the attachment of muscles commensurate with the extent of the supposed wing. The arm-bone and the bones which we presume to be the scapula and coracoid, bear some correspondence to the extent of the wing: but the extraordinary circumstance of all is the size and strength of the bones of the jaw and vertebræ of the neck, compared with the smallness of the body and the extreme delicacy of the ribs; which makes this altogether a being the most incomprehensible in nature.

OF THE RADIUS AND ULNA.

The easy motion of the hand, we might imagine to result from the structure of the hand itself; but, on the contrary, the movements which appear to belong to it, are divided among all the bones of the extremity.*

The head of the arm-bone is rotatory on the shoulder-blade, as when making the guards in fencing; but the easier and finer rolling of the wrist is accomplished by the motion of one bone of the fore-arm upon the other. The ulna has a hooked process, the olecranon, or projecting bone of the elbow, which catches round the lower end of the arm-bone (this articulating portion being called trochlea), and forms with it a hinge joint, for bending and extending the fore-arm. The radius, again, at the elbow, has a small, neat, round head, which is bound to the

In the sketch (p. 55) the bone | dius; in revolving on the lower bone, with the hand joined to it is the ra- the ulna, it carries the hand with it.

ulna by ligaments, as a spindle is held in the bush; and it has a depression with a polished surface for revolving on the condyle of the humerus; at the wrist it has also a surface adapted for rotation: accordingly the radius turns on its long axis, rolling upon the ulna both at the elbow and wrist-joint; and, as it turns, it carries the hand with it, because the hand is strictly attached to its lower head alone. This rolling is what are termed pronation and supination.

Such freedom of motion, in an animal with a solid hoof, would be useless, and a source of weakness; hence, in the horse, the radius and ulna are united, and consolidated in the position of pronation.

But before taking any particular instance, let us extend our views. There is, indeed, something so highly interesting in the conformation of the whole skeleton of an animal, and the adaptation of each part to all the others, that we must not let our reader remain ignorant of the facts, and the more important conclusions drawn from them. What we have to state has been the result of the studies of many comparative anatomists; but none has seized upon it, with the privilege of genius, in the masterly manner of Cuvier.

Suppose a man, ignorant of anatomy, to pick up a fragment of bone in an unexplored country; he learns nothing, except that some animal has lived and died there; but the anatomist, judging from that portion of bone, can not merely estimate the size of the extremity of the animal as well as if he saw the print of its foot, but he can predicate the form of the joints of the skeleton, the structure of its jaws and teeth, the nature of its

food, and its internal economy. This, to one unacquainted with the subject, must appear wonderful; but it is after the following manner that the anatomist proceeds. Let us suppose that he has taken up that portion of bone, in the limb of a quadruped, which corresponds to the upper part of the human radius ; and that he finds that the form of the end of the bone, where it enters into the joint, does not admit of the free motion, in various directions, possessed by the paw of the carnivorous creature. It is obvious, on that view of the structure alone, that the office of the limb must have been for supporting the animal, and for progression, not for seizing prey. That leads him to the fact, that the bones corresponding to those of the hand and fingers, must have differed from the bones of the paw of the tiger; for the motions which that conformation permits, would be useless without rotation of the wrist: and he concludes, therefore, that the hand and finger-bones were each formed in one mass, like the cannon, pastern, and coffin bones of the horse's foot.* Now, the motion of the foot of a hoofed animal being limited to flexion and extension, it implies restrained motion at the shoulder-joint, and absence of a collarbone. And thus, from the broken specimen in his hand, the naturalist acquires a perfect notion of the bones of both extremities. But the motion of the extremities implies a particular construction of the vertebral column which unites them; each bone of the spine will be of that form which corresponds to the bounding of the stag, or galloping of the horse; but will not have the kind of articulation which admits of the turning or writhing of the body, as in the leopard or tiger.

Next he comes to the head :—and he argues that the pointed, cutting teeth, with which a carnivorous animal is provided to rend its prey, would be useless, unless there were mobility of the extremities, like that of the hand, for grasping it, and claws for securing it. He considers, therefore, that the front teeth must have been for browsing, and the back teeth for grinding. But the socketing of the teeth requires a peculiar shape of the jaw-bones, and the muscles which move these bones must also be peculiar. In short, from the shape and functions of the

* These are solid bones, in which | fingers; yet comparative anatomy it is difficult to recognise any resem- proves that they are analogous. blance to the bones of the hand and

mouth, he forms a conception of the figure of the skull. From that point he may set out anew; for from the form of the teeth, he may deduce the nature of the stomach, the length of the intestines, and all the peculiarities which mark a vegetable feeder, as contrasted with one of the carnivora.

Thus the whole parts of the animal system are so connected with one another, that from one single bone or fragment of bone, be it of the jaw, or of the spine, or of the extremity, a really accurate conception of the shape, motions, and habits of the animal may be formed.

It will readily be understood that by the same process of reasoning, we may ascertain, from a small portion of a skeleton, the existence of a carnivorous animal, or of a fowl, or of a bat, or of a lizard, or of a fish. And what a conviction is here brought home to us of the extent of that plan, which, pervading the whole range of animated beings whose motions are conducted by the operation of muscles and bones, yet adapts the members of every creature to their proper office!

After all, this is but a part of the wonders disclosed through the knowledge of an object so despised as a fragment of bone. It carries us into another science. The knowledge of the skeleton not only teaches us the classification of animals now alive, but affords proofs of the former existence of animated beings which are no longer found on the surface of the earth. We are thus led from such premises to an unexpected conclusion. Not merely do we learn that individual animals, or races of animals, now extinct, existed at those distant periods: but even the changes which the globe has undergone, in time before all existing records, and before the creation of human beings to inhabit the earth, are opened to our contemplation.

B

To return to our particular subject, we readily comprehend how, if the geologist should find the head of a radius, resembling this sketch, and see a smooth depression (A), on its extremity, where it bears against the humerus, and a polished circle (B), where it turns on the cavity of the ulna, he would say,—this animal had a paw-it had a motion

Upper End of a Radius.

A

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