THE ANCESTORS OF THE HORSE 



more complex in the pattern which they show 

 when worn down. In Fig. 97 crowns of the 



Fig. 96. — Skeleton of the Phenacodus, a five-toed Eocene 

 animal related to the ancestors of the horse. 



cheek-teeth of the Mesohippus are represented, 

 and in Fig. 98 the crown of an upper molar of 





F]G. 97. — Cheek-teeth, or molars, of the upper and lower jaw, 

 left side, of Mesohippus Bairdii, from the Middle Oligo- 

 cene of South Dakota. 



a recent horse. There are a great number of 



141 



