THE ANATOMY OF A BIBD 11 



of a tree, a mechanism which is shared by that, in some oth^r 

 respects, bii'd-like lizard, the chameleon. A foot of this kind is 

 technically called * zygodactyly' A singular modification of the 

 foot is seen in the Kingfisher (fig. 7) where the two middle toes are 

 enclosed in the same fold of skin ; this is called syngenesious.' 



Skeleton. 



A bird's skeleton is wonderfully light and spongy in texture. It 

 is fill of air (see below, p. 27), but deficient in marrow. Its entire 

 structure is pre-eminently suited to a flying creature, not only for the 

 above reasons, but because the heaviest part (the sternum) lies in 

 the middle, in the centre of gravity, and thus assists in preserving 

 the balance, lil^e Blondin's pole. 



The Skull. 



The skull of a bird is composed of a large number of separate 

 bones, which are very closely united in the adult bird, so much s6 

 that it is next to impossible to recognise that they are distinct bones. 

 The bones are also thin and light, for to a flying animal any weight 

 forward would be most disadvantageous. The weight of the bird 

 should be, and is, concentrated in the middle of the body. We can 

 divide the skull into two regions : behind is the smooth, rounded 

 brain-case or cranium ; in front is the face, which is largely en- 

 sheathed by the beak. It is chiefly formed by the maxillary and 

 nasal bones above, and by the palatine and pterygoids below. The 

 length of this part of the skull is subject to great variation in different 

 birds. In the Storks, for instance, the face is extremely long, while 

 in the Parrots it is comparatively short. 



Professor Huxley, about thirty years ago, proposed to classify birds 

 by the form of the bones of the palate. In the skuU of the Hawk, 

 it will be seen that two bones lying in the front region of the palate 

 are fused with each other in the middle line, and to the type of skuU 

 which is thus characterised the name ' desmognathous ' was given. 

 It is found not only in the Hawks, but in a quantity of other birds ; 

 for instance, in the Stork tribe, and in the HombiUs and Toucans. 

 The second form of skull distinguishes the gallinaceous birds ; in 

 them the two maxiUo -palatines remain unconnected, and the palate 

 is therefore in a way cleft ; this is termed the ' schizognathous ' 



