HISTORY OF THE HORSE 



59 



cusps almost completely converted into crescents and 

 crests, with another premolar tooth becoming like the 

 molars. There are four toes in front and three behind, 

 but the central toe in each foot is larger, stronger and 

 more important than the toes on either side. 



6 and 7. Mesohippus. — From the Middle and Upper 

 Oligocene. There are three toes on each foot and a splint 

 representing a fifth toe on the forefoot. The middle toe 



THE EVOLUTION OF THE HORSE 



FIG. 48.— CHANGES IN THE SKULL, TEETH AND FEET SHOWING EVOLU- 

 TION OF THE HORSE 



has become much larger than the side toes, which bear 

 very little of the weight of the body. Three of the pre- 

 molars have become like full molars, with crests on the 

 crown completely formed. The outside crests in the 

 upper molars have taken the shape of two crescents. The 

 animals found in the Middle Oligocene were about the 

 size of a coyote, while those of the Upper Oligocene were 

 as large as a sheep. Of these species all parts of the 

 skeleton are known. 



8. Anchithenum. — From the Lower Miocene. This 

 stage is much like the Mesohippus, but is larger and has 



