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- 
