THE STORY OF THE HORSE 227 



thumb, was first raised off the ground and rendered 

 useless, while a similar change came over the corre- 

 sponding toe on the hind foot. The hard work of 

 running being done on the latter, this superfluous toe 

 was more detrimental there than on the front foot, 

 and disappeared, consequently, more rapidly. In time, 

 however, it also disappeared from the front foot. 

 Gradually the further elevation of the foot lifted the 

 toe, which corresponds to our little finger, off the 

 ground, and this now disappears also. 



With increasing toughness of the grasses, as the cli- 

 mate becomes drier and the region more elevated, the 

 teeth of the horse are given harder work. The points 

 begin to spread into ridges and to unite with each 

 other in such way as to form the crescents, which are 

 later to be so characteristic of the teeth of the modern 

 horse. 



By the middle of the Tertiary this ancestral horse 

 has risen in height until he is taller and heavier than 

 a setter dog. Three toes are found on each front foot. 

 The middle toe is getting constantly more developed, 

 though the smaller toes are evidently still of use. 

 The ridges of the teeth are quite crescentic now on 

 the outer side, and becoming better adapted to the 

 evidently firmer food which the creature is obliged to 

 eat. 



As we come toward the end of the Tertiary, the de- 



