HISTORY OF THE PERISSODACTYLA 



303 



functional digits and indication of a splint, and splints, 

 as the whole history of the long series teaches, always are 

 found to be functional digits in the ancestor ; the hind foot had 

 three toes and perhaps two splints. This preceding form 

 is hardly to be looked for in America or Europe ; it will be 

 found, if ever, in the region whence the great migration came. 



Fig. 153. — The "Dawn Horse " (fBohippus) of the lower Eocene. Restored from a 

 skeleton in the American Museum. 



In all other respects, as well, jEohippus was what we should 

 expect the forerunner of the Wind River and Bridger horses to 

 be. The premolars were all smaller and simpler than the 

 molars and the latter in the upper jaw are particularly interest- 

 ing, for they had no crests and ridges of enamel, but four prin- 

 cipal conical cusps, arranged in two transverse pairs, and be- 

 tween the cusps of each pair was a tiny cuspule no bigger than 

 the head of a pin. These cuspules were the first step in the for- 

 mation of the transverse crests, which were destined to assume 

 such importance in the subsequent members of the series. The 



