296 



EVOLUTION OF THE HORSE, 



Although the Hyracotherium had four toes on its front 

 feet, it may be considered to have been an odd-toed animal ; 

 for one of these digits was off the ground, and was conse- 

 quently functionless. 



The foot of the rhinoceros (Fig. 390) shows a marked 

 tendency to become one-toed. Being three-toed on its fore, 

 as well as on its hind feet, it belongs to a less ancient type 

 than the tapir. The Acerotherium (Fig. 391) was a prob- 



FiG. 390. — Fore Foot of 

 Rhinoceros (|th real length). 



Fig. 391.— (4//^r Gaudry.) Left 

 Fore Foot of Acerotherium 

 Tetrad ACTYLUM Qth real length). 



able ancestor of the rhinoceros, if not of the horse. The 

 Brontotheriwn, which has been found in the Miocene of 

 Colorado, had, like the tapir, four digits on its front feet, 

 and three on its hind ones (Figs. 392 and 393). 



