B48 ANIMAL LIFE 



ancestor of our horse was a three-toed uigulate scarcely 

 larger than a sheep and with teeth adapted to feed on succu- 

 lent vegetation, such as the warm, moist climate of those 

 early days afforded. As the ground, then wet and swampy, 

 became hard, and the juicy vegetation gave way to the 

 dryer grasses, the lateral toes became shorter in certain 



FIG. 389. Skeleton of Mesohippus bairdi, the three-toed ancestor of our horse. 

 This animal was about the size of a sheep. After Farr. 



individuals, and the third digit grew longer and stronger, 

 thus enabling them to escape their carnivorous pursuers, 

 while all those individuals whose limbs and teeth did not 

 vary so as to aid them to escape the increasing carnivorous 

 animals and masticate the dry grasses, were exterminated. 

 Thus age after age those horses whose lateral toes became 

 smaller while the third one grew longer, giving them greater 

 speed, persisted and multiplied, but those with large, lateral 



