58 MANAGEMENT AND BREEDING OF HORSES 



western states. Of some stages all parts of the skeleton 

 have been found, while of others only the jaws, or jaws 

 and feet, have been discovered. The stages properly- 

 grouped are as follows :* 



1. Hyracotherium. — From the Lower Eocene. This is 

 the most primitive stage known, and only the skull has 

 been found, so that it has not been determined what the 

 feet were like. The teeth display six rounded cusps on 

 the upper molars and four on the lower. The premolar 

 teeth have only one main cusp, except the third and fourth 

 premolars, in each jaw, which have two and three respec- 

 tively. The animals were no larger than the domestic 

 cat. Found only in London clay, England. 



2. Eohippus. — From the Lower Eocene. Teeth vary 

 somewhat from above, the molars having the cusps more 

 clearly fused into cross-crests, and the last premolar is 

 beginning to look like one of the true molars. The fore- 

 foot has four complete toes and the splint of a fifth. The 

 hindfoot has three complete toes and splint. The 

 animals were about the size of a fox terrier dog and 

 known as "Dawn Horses." Found in New Mexico and 

 Wyoming. 



3 and 4. Protorohippus and Orohippus. — From the 

 Middle Eocene. In these animals the splints have dis- 

 appeared, leaving complete toes, as in the Eohippus. The 

 crests in the molars are more apparent, and the last pre- 

 molar has become almost like the molars, while the next 

 to the last premolar is beginning to assume a similar form. 

 This type was about the size of a small dog, perhaps about 

 14 inches high. The Protorohippus was found in 1880 in 

 the Wind River Badlands of Wyoming and was described 

 under the name of the "Four-Toed Horse." 



5. Epihippus. — From the Upper Eocene. Only incom- 

 plete specimens have been found of this stage of the 

 evolution of the horse. The molar teeth have the round 



•Made up from Guide Leaflet, No. 9. American Museum of Natural History, 

 W. D. Matthew. 



