569 



Fig. 477. Dinori-rnx minihilt', restoration of skeleton by Marsh; about 13 feet 

 long. Middle Korcne, Wyoming. 



tms fell out of use and were atrophied. The first class reached its 

 t'xtrrme type at length in the horse, and the second in our cloven- 

 hoofed cattle; but these perfected types were not attained in the 

 Eocene. 



The horse has become a classic example of evolution. The 



Fig. 478. An early ancestor of the horse family, Ilyrucothcrium (Prntorohippus) 

 irntiiolum, from the Lower Eocene (Wind River formation) of Wyoming; about % 

 natural size. (Cope.) 



earliest recognized form was the Hyracothcrinm (Fig. 478), which 

 resembled the horse but little. The Orohippus (Epikippus) repre- 

 sented a greater advance. It was four-toed (three functional) in 



