4 SKELETON OF THE BlUB. 



giraffe and the short one of the eleplianl being obtained by the prolongation of the seven ver- 

 tebrae in the former ami their compression in the latter. En the birds, however, tin 're are never 

 less than nine vertebrae in the neck, and in some cases the number is considerably greater ; the 

 swan, for example, possessing no less than twenty-three of these bones. The neck is also 

 much longer in the birds, being in many instances longer than the remainder of the body. 

 The vertebra' of the neck are extremely flexible, as is needful for the peculiar habits of birds ; 

 but those of the back are immovably connected with each other, and in many cases are even 

 fused together. The seven or eight short vertebra' which form the tail are movable, and are 

 generally terminated by a. single bone of greater length than any of the others. 



We now proceed to the breast and body. The ribs are chiefly remarkable for a, flat 

 appendage which starts from the lower portion of the hone, ami is directed backwards, so that 

 it overlaps each succeeding rib. The breast bone is placed lower than might be supposed 

 from the external aspect of a bird, ami is of very great size. Its substance is much flattened, 

 and it possesses a strong ridge or keel of bone, which varies in its depth according to the powers 

 of flight possessed by the particular species to which it belongs. As the eagle is a strong- 

 winged bird, the keel is very prominent, but in such non-flying birds as the ostrich and the 

 apteryx, there is no keel at all. Between the breast bone and the neck lie four clavicles, or 

 collar bones, differing much in size and shape in the various species of birds. One set of them, 

 technically called the os fwrculare, from its forked shape, is sometimes absent, its place being 

 supplied by a ligament ; but the others, termed the claviculct coracoidce, are invariably 

 present. These two sets of bones are familiar to all who have carved a fowl, under the terms 

 of "merry-thought" and "neck bones." 



The limits now come before our notice, and we cannot but be struck with the curious fact, 

 that in the birds the bipedal mode of walking again makes its appearance, having disappeared 

 tlirough all the mammalia with the exception of man. There is, however, this analogy between 

 the lower mammals and the birds, namely, that in both instances the anterior limbs are intended 

 for progression, although in the one case these formations belong to earth, and in the other to 

 the aii-. The bones of the wing present a considerable resemblance to those of a man's arm, as 

 may be seen by comparing the skeleton of The eagle with that of the man in Volume I. The 

 upper arm bone is of various lengths in the different birds, being of wonderful proportions in 

 such long-winged birds as the albatross, but very short in the penguins, the cassowary, and 

 many other birds. The two bones of the fore-arm. technically called the ulna and radius, 

 are also long in the long-winged birds, and serve to carry a large expanse of feathers. Of 

 these two, the ulna is the larger and more cylindrical. To the end of the ulna and radius are 

 jointed the two little bones of the wrist, which bear a quasi hand, composed of a thumb and 

 two tinners. The thumb is very small, consisting of either one or two bones ; and the fingers, 

 which are only needed for the purpose of bearing feathers, are also small. One of them is 

 composed of either two or three joints, but the other is a very little one, being but one single 

 pointed bone. 



The bones of the legs are very similar in their arrangement to those of the mammalian 

 quadrupeds, although they are subject to certain modifications, especially at their extremities. 

 The thigh-bone is tolerably strong and cylindrical, but of no very great length, in proportion 

 to the size of the bird or the length of its limbs. Even in the curious stilt-plover, where the 

 legs are of such extraordinary length, the thigh-bone is comparatively short, and not visible 

 outside the feathers. The leg-bone, or "tibia." is always the longest bone of the limb, and 

 is accompanied by a very small and undeveloped "fibula," which is only attached to its upper 

 extremity, and tapers gradually to a point. The "instep," as we should term it in a human 

 foot, is merely a single bone, jointed at its upper extremity to the tibia, and its lower to the 

 bones of the toes. In general, birds are furnished with four toes on each foot, but there are 

 several exceptions to rhis rule, among which the ostrich is the most conspicuous. 



Not only do the bones of a bird differ in external form from those of a mammal, but they 

 are also considerably modified in their structure. In the mammals the bones are heavy, solid, 

 and their centre is tilled with marrow ; but in the birds the bones are of a much lighter make, 

 and many, such as the upper wing bone, the breast bone, and pail of the skull, are. moreover, 



