4 SKELETON OF THE BIRD. 



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

 tebrae in the former and their compression in the latter. In the birds, however, there are never 

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

 swan, for examj^le, 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 vertebrge of the neck are extremely llexil)le, as is needful for the peculiar habits of birds; 

 but those of the back are immova))ly connected with each other, and iu many cases are even 

 fused together. The seven or eight short vertebrje which form the taU 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 

 api>endage whicli starts from the lower portion of the boue, and is directed backwards, so that 

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

 from the external asj^ect of a bird, and 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 Itone and the neck lie four clavicles, or 

 collar bones, difl'ering mucli in size and shape in the various species of birds. One set of them, 

 technically called tlie osfwrciUare, ixani its forked shape, is sometimes absent, its place being 

 supplied by a ligament ; but the others, termed the clcmiculce coracotdce, are invariably 

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

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



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

 that in the birds the bipedal mode of walking again makes its aj^pearance, having disappeared 

 tlu'ough all the mammalia with the exception of man. There is, however, this analogy between 

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

 for i^rogression, although in the one case these formations belong to earth, and in the other to 

 the air. The bones of tlie 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 iu 

 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 exjianse of feathers. Of 

 these two, the ulna is the larger and more cylindrical. To the end of the ulna and radius ai'e 

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

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

 whicli 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 liones of the legs are very similar in their arrangement to those of the mammalian 

 quadrupeds, although they are subject to certain modiflcations, 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 Umbs. 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. Tlie 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 ujiper 

 extremity, and tapers gradually to a point. The "instep," as we sliould 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 this 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 filled 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 part of the skull, are, moreover, 



