126 



HYPOTHESIS OF THE DEVELOPMENT OF 



a strong analogy of form to the human being ; its head, its 

 forelegs, its hinder extremities, have each their representative 

 parts in our frame. But the ordinary observer is surprised to 

 learn how much further the principle is carried. For example, 

 the hind leg of the horse looks very different from one of our 

 limbs, in as far as it seems to have a knee presented back- 

 wards, and possesses no toes. In reality, the part of the horse 

 corresponding to our knee is high up near the body of the 

 animal, and the hock corresponds to our heel. It has toes, 

 moreover ; but they are sunk in the hollow of a hoof, which 

 serves as a shield to that part. The horse, the dog, and many 

 other quadrupeds, may be said to walk upon their toes (hence 

 called digitigrade) : others, as the bear and badger, present the 

 whole foot to the ground, as man does (hence called planti- 

 grade). Thus, too, the wing of the bird contains bones repre- 

 senting those of our arm, though modified for so different a 

 purpose. The paddles of the whale tribes and seals are other 

 curious modifications of a member substantially the same. 



FIG. 73. 



C D 



F 



Different forms of Anterior Member : 

 A, Fish; B, Bird; C, Dolphin;!), Deer;E, at;F, Man. 



The bat, again, has the bones of its hand developed to an un- 

 usual extent, so as to become a frame for the membrane by 



