134 THE INFANCY OF ANIMALS 



then, we have another demonstration of the way ancestral 

 characters appear, and vanish during the life-history of 

 their descendants. But this by the way. 



After such a comparison there could be no doubt about 

 the identity of these ankle and foot bones in the two 

 creatures — bird and reptile. But the story is not complete. 

 If this ancient reptile helps us to interpret the bird, so the 

 bird, on the other hand, helps us to interpret the reptile. 

 For in all other reptiles, as in the more highly organised 

 mammals, of whom man is the chief ornament, the ankle- 

 bones are represented not by two, but a number of separate 

 bones, arranged in two rows. In the reptile, whether the 

 ankle-bones be few or many, and in the bird, the hinge or 

 joint between the shank and the foot is formed between 

 these two rows ; in the mammal it is formed between the 

 uppermost row and the shank. 



But how is it that the fossil reptile and the bird agree, 

 and differ from all living reptiles in having but two 

 separate ankle-bones — in the adult bird indeed even these 

 seem to have vanished ? To answer this we must examine 

 the foot of the embryo bird. Here we may find as many 

 as six separate bones, though represented only in soft 

 cartilage, two forming the upper and four the lower row. 

 But speedily these separate elements blend together, and 

 later come to form the mallet, and the oval disc with which 

 we started. Thus, then, we may gather from this study of 

 the leg of the young bird, that there exists an undoubted 

 relationship with the reptiles, and more particularly with 

 the dinosaurs : and this evidence could be further supple- 

 mented by a study of the rest of the leg. 



The wing of the young bird tells us little in regard to this 

 reptilian ancestry ; but it throws a flood of light on the 

 past history of its evolution. Some evidence of this has 



