There can be no greater contrast to these bones of the mole than is presented in the skeleton of the bat. In this animal the

bones are light

bones of the upper extremity in the bat, we might be led to say, on comparing it with the wing of a bird, that it was an awkward attempt "a failure." But before giving expression to such an opinion, we must understand the objects required in this construction. The wing of the bat is not intended merely for flight: it is so formed that while it can sustain the animal in flying, it shall be capable also of receiving a new sensation on its surface, or sensations of such an exquisite degree of fineness as almost to constitute a new sense. On the thin web of the bat's wing numerous nerves are distributed; and the use of these is to enable the animal, during the obscurity of night, when both eyes and ears fail, to avoid objects in its flight. Could the wing

a wedge, to assist in burrowing and | in other animals, to assist in moving throwing aside the earth. The conformation of the head, and the strength of its bones, and the new adjustment of the muscle (the platysma myoides), which is cutaneous

the head, are among the curious changes of common parts for enabling them to perform new offices. See again the "Additional Illustrations" in the Appendix.

of a bird, covered with feathers, do this? Here then we have another example of the necessity of taking every circumstance

into consideration before presum

ing to criticise the ways of nature. It is a lesson of humility.*

We have here a sketch of the arm-bone of the Ant-eater, † to show once more the correspondence maintained throughout all the parts of an extremity. We observe these extraordinary spines standing off from the humerus. Now, these indicate the power of the muscles attached to the bone; for, as I have said before, whether we examine the human body, or the forms of the bones in the lower animals, the distinctness with which the spines and processes are marked, declares the strength of the muscles. It is particularly pleasing to notice here the correspondence between the humerus and all the other bones, how large, in the first place, the scapula is, and how it has a double spine, with great processes: how remark

Besides the adaptation of the bat for flight, by the adjustment of the bones of its arm, this animal has a series of cells situated under its skin. I know not whether I am correct or not in saying that these are analogous to the aircells of birds, and serve to make the bat specifically lighter. In some species they extend over the breast, and into the arm-pits, and are filled by an orifice which communicates with the throat.

I have adverted to the provisions in the bones of the shoulder of the bird to give firmness to the joint, seeing that it is the centre of motion for the wing. Now, although the bat has not the same arrangement of bones as

the D

ably the ulna projects at the olecranon or elbow, while the radius is still free for rotating: but above all, we cannot fail to observe in the development of one grand metacarpal bone and its corresponding phalanges, to the last of which a strong claw is attached, a most efficient instrument for scratching and turning aside an ant-hill. The whole, therefore, is an example of the relation of the particular parts of the extremity to one another; and were it our business, it would be easy to show that as there is a correspondence among the bones of the arm, so is there a more universal relation between those of the whole skeleton. As the structure of the bones of the arm declares the extremity to be adapted for digging into ant-hills, so we shall not be disappointed in our expectation of finding that the animal has a projecting muzzle unarmed with teeth, and a long tongue provided with a glutinous secretion, to lick up the emmets disturbed by its scratching.

In the skeleton of the Cape-mole, we may see, in the projection of the acromion scapula, and a remarkable process in the middle of the humerus, a provision for the rotation of the arm; which implies burrowing. But the apparatus is by no means so perfect as in the common mole; so that we may infer that the Cape-mole digs in a softer soil, whilst the possession of gnawing teeth indicates that it subsists on roots.

In BIRDS, there is altogether a new condition of the osseous system, 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, should be specifically light; secondly, the capacity of their chest must be extended, and the motions of their ribs limited, so 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 for breathing. The lungs are highly vascular and spongy, but they are not capable of being distended with air; the air is drawn through their substance, passing, by means of numerous orifices, into cells under their skin, and even filling the interior of their bones; so that whilst the great office of decarbonisation of the blood is securely performed, advantage is taken to let the air, warmed and rarefied by the high temperature of their bodies, into all their cavities.

From what was said, in the introductory chapter, of the weight of the body being a necessary concomitant of muscular strength, we see why the lightness of the bird, as well as the conformation of its skeleton, may be a reason for its walking badly. On the other hand, in observing how that lightness is adapted for flight, it is remarkable what a small addition to the weight will prevent the bird from rising on the wing. If the griffon-vulture be scared after his repast, he must disgorge before he can fly; and so with the condor,-if found in the same circumstances, he can be taken by the Indians, like a quadruped, by throwing the lasso over his neck.*

As every one must have observed, the breast-bone of the bird extends the whole length of the body, covering the great cavity, common to the chest and abdomen, into which the air is admitted. Now, it follows from this extension of the breast-bone, that a lesser degree of motion suffices for respiration; accordingly, a greater surface is obtained for the lodgment and attachment of the muscles of the wings, whilst that surface being less disturbed by the action of breathing, is more steady. Another peculiarity of the skeleton of the bird is, that the vertebræ, instead of being moveable on each other, are consolidated: an additional proof, if any were now required, of the whole system of bones conforming to that of the extremities; because, to give effect to the action of the muscles of the wings, it is necessary that all the bones of the trunk to which they are attached should be united firmly together.t

From the vertebræ of the bird being thus fixed, and the pelvis reaching high, no motion can take place in the body; indeed, if there were any mobility in the back, it would be interrupted by the sternum or breast-bone. We cannot but admire, therefore, the structure of the neck and head; how the length and pliability of the vertebræ of the neck not only give to the bill the extent of motion and office of a hand, but, by enabling the bird to preserve its balance in standing, running, or flying, become a substitute for the loss of flexibility in the body. Is it not curious to observe how the whole skeleton is adapted to this one object, the power of the wings! Whilst the ostrich and other "

runners" have not got a keel

The ostrich and cassowary, which

* The subject is continued in the are runners, have the spine loose.

"Additional Illustrations."

in their breast-bone, birds of passage are recognisable by the depth of the ridge of the sternum. The reason is, that the

angular space formed by that process and the body of the bone affords lodgment 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 perceive 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, in migrating, require a wind that blows against them, it implies an extraordinary power, as well as continuance, of muscular exertion.

* Borelli makes the pectoral mus- | cles of a bird exceed in weight all the other muscles taken together; whilst he calculates that in man the pectoral muscles are but a seventieth part of the mass of muscles.

Mr White says truly that the swift lives on the wing; it eats, drinks, and collects materials for its nest while flying, and never rests but during darkness. No bird equals the humming-bird in its powers of

flight, and, accordingly, it has a broader sternum, and a greater prominence of keel, in proportion to its size, than any other bird. It may be mentioned, that in the sternum of the bat a very distinct ridge is developed, corresponding with the keel of the bird.

It is possible that the wind blowing near the ground in one direction, may be attended with a current of a higher stratum of the atmosphere in