shall not be disappointed in our expectation of finding a projecting muzzle unarmed with teeth, and a long tongue provided with a glutinous secretion, to lick up the emmets which are disturbed by the animal's scratching.

In the skeleton of the cape-mole, we may see, from the projecting acromion scapulæ, and a remarkable process of the humerus, that there is a provision for the rotation of the arm, which implies burrowing. But the apparatus seems by no means so perfect as in the mole, implying that it digs in a softer soil than that animal, whilst the possession of gnawing teeth indicates that it lives on roots.

In BIRDS there is altogether a new condition of parts, as there is a new element to contend with. The very peculiar form and structure of their skeleton may be thus accounted for. First, it is necessary that birds, as they are buoyed in the air, be specifically lighter. Secondly, the circumference of their thorax must be extended, and the motions of their ribs limited, that the muscles of the

wings may have sufficient space and firmness for their attachment. Both these objects are attained by a modification of the apparatus of breathing. The lungs are highly vascular and spongy, but they are not distended with air. The air is drawn through their substance into the large cavity common to the chest and abdomen; and whilst the great office of decarbonization of the blood is securely performed, advantage is taken to let the air into all the cavities, even into those of the bones. From what was said in the introductory chapter, of the weight of the body being a necessary concomitant of muscular strength, we see why birds, by reason of their lightness, as well as by the conformation of their skeleton, walk badly. And, on the other hand, in observing how this lightness is adapted for flight, it is remarkable how small an addition to their body will prevent them rising on the wing. If the griffon-vulture be frightened after his repast, he must disgorge, before he flies; and the condor, in the same circumstances, is taken by the Indians, like a quadruped, by throwing the lasso over it.*

As every one must have observed, the breast-bone of birds extends the whole length of the body; and owing to this extension, a lesser degree of motion suffices to respiration. So that a greater surface, necessary for the lodgement and attachment of the muscles of the wings, is obtained, whilst that surface is less disturbed by the action of breathing, and is more steady. Another peculiarity of the skeleton of the bird is the consolidation of the vertebræ of the back; a proof, if any were now necessary, that the whole system of bones conforms to that of the extremities, the firmer texture of the bones of the trunk, being a part of the provision for the attachment of the muscles of the wings.†

The vertebræ of the back being fixed in birds, and the pelvis reaching high, there is no motion in the body; indeed, if there were, it would be interrupted by the sternum. We cannot but admire, therefore, the composition of the neck and head, and how the extension of the vertebræ, and the length and pliability of the neck, whilst they give to the bill the office of a hand, become a substitution for the loss of motion in the body, by balancing the whole, as in standing, running, or flying. Is it not curious to observe how the whole skeleton is adapted to this one object, the power of the wings?

Whilst the ostrich has no keel in its breast-bone, birds of passage are, on dissection, recognisable by the depth of this ridge of the sternum. The reason is that the angle, formed by this process and

*It is interesting to notice the relations of great functions in the animal economy. Birds are oviparous, because they never could have risen on the wing had they been viviparous; if the full stomach of a carnivorous bird retard its flight, we perceive that it could not have carried its young. The light body, the quill-feathers, the bill, and the laying of eggs, are all necessarily connected.

The ostrich and cassowary, which are rather runners than fliers, have the

spine loose.

the body of the bone, affords lodgement for the pectoral muscle, the powerful muscle of the wing. In this sketch of the dissection of the swallow, there is a curious resemblance to the human arm, and we cannot fail to observe, that the pectoral muscle constitutes the greater part of the bulk of the body. And here we see the correspondence between the strength of this muscle and the rate of flying of the swallow, which is a mile in a minute, for ten hours every day, or six hundred miles a day. If it be true that birds, when migrating, require a wind that blows against them, it implies an extraordinary power, as well as continuance of muscular exertion.

We see how Nature completes her work, when the intention is that the animal shall rise buoyant and powerful in the air-the whole texture of the frame is altered and made light, in a manner consistent with strength. We see also how the mechanism of the anterior extremity is changed, and the muscles of the trunk differently directed. But we are tempted to examine those means, which we would almost say are more awkwardly suited for their purpose, where the system of bones and muscles, peculiar to the quadruped, is preserved, while a power of launching into the air is also given. We have already noticed the structure of the bat as adapted to flight; but there are other animals which enjoy this function in a lesser degree. For example, the flying squirrel (Petromys Volucella,) being chased to the end of the bough, spreads out its mantle from one extremity to the other, and drops in the air; but with such a resistance from its extended skin and its tail, that it can direct its flight obliquely downwards, and even turn in the air. But to this end, there is no necessity for any adaptation of the anterior extremity. Among reptiles there is a provision of the same kind, in the Draco fimbriatus; which is capable of creeping to a height, and dropping safely to the ground, under the protection of a sort of parachute, formed by its extended skin. This is not an inapt illustration, for although the phalanges of the fingers are not here used to extend the web, the ribs, which are unnecessary for breathing, are prolonged like the whalebone of an umbrella, and on them the skin is expanded. But this brings us to a very curious subject, the condition of those Saurian reptiles, the remains of which are found only in a fossil state, in what are termed the ancient strata of the Jura. The Pterodactyle of Cuvier is an animal which seems to confound all our notions of system. 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. It had the bones of the anterior extremity prolonged,

• Borelli makes the pectoral muscles of a bird, exceed in weight all the other muscles taken together; whilst the pectoral muscles of man, are but a seventieth part of the whole mass of the muscles.

Mr. White says truly, that the swift lives on the wing; it eats, drinks, and collects materials for its nest in flying, and never rests but during darkness.

and fashioned somewhat like those in the wing of a bird; but it could not have had feathers, as it had not a proper bill. We see no creature having feathers without a bill to dress and prim them. Nor did this extremity resemble the structure in that of a bat: instead of the phalanges being equally prolonged, the second only was extended to an extraordinary length, whilst the third, fourth, and fifth remained with the length and articulation of a quadruped, and with sharp nails, corresponding with the pointed teeth. The extended metacarpal bone reached double the whole length of the animal, and the conjecture is, that upon it was extended a membrane, resembling that of the Draco fimbriatus. In the imperfect specimens which we have, we cannot discover in the height of the pelvis, the strength of the vertebræ of the back, or the expansion of the sternum, a provision for the attachment of muscles commensurate with the extent of the supposed wing. The humerus, and the bones, which we presume are 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 make it, altogether, the thing most incomprehensible in nature.

OF THE RADIUS AND ULNA.

The easy motion of the hand, we might imagine to be in 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 humerus is rotatory on the scapula, as when making the guards in fencing; but the easier and finer rolling of the wrist is accomplished by the motion of the radius on the ulna.

The ulna has a hooked process, the olecranon, which catches round the lower end of the humerus or arm-bone, (this articulating portion is called trochlea), and forms with it a hinge-joint. The radius, again, has a small, neat, round head, which is bound to the ulna by ligaments, as a spindle is held in the bush. This bone turns on its axis and, as it turns, carries the hand with it, because the hand is strictly attached to its lower head alone. This rolling, is what is termed pronation and supination.

Such a motion would be useless, and a source of weakness in an animal that had a solid hoof. Accordingly, in the horse, these bones are united together and consolidated in the position of pronation.

It is interesting to find that by studying the processes of the bones,

*In the sketch in the next page, the upper bone of the fore-arm is the radius, and in revolving on the lower bone, the ulna, it carries the hand with it.

than which nothing, at first sight, appears more inconsequent, we are learning the characters of a language which shall enable us to read monuments of the highest interest; the records of the creation, which give an account of the revolutions of the earth itself.

If a geologist should find the nearer head of the radius, and see in the extremity of it a smooth depression, where it bears against the humerus, and observe the polished circle that turns on the cavity of the ulna, he would say,-This animal had a paw-it had a motion at the wrist, which implies claws. Claws may belong to two species of animals; the feline, which is possessed of sharp carnivorous teeth, or to animals without teeth. If he should find the lower extremity of this same bone, and observe on it spines and grooves for the distinct tendons which disperse to the phalanges, he would conclude that there must have been moveable claws-that it belonged to a carnivorous animal; and he would seek for canine teeth of a corresponding size.