EVOLUTION OF THE HORSE 15 



and these are just beginning to show signs of fusing into cross- 

 crests. The premolar teeth have only one main cusp, except the 

 third and fourth premolars (next the molars) in each jaw, which 

 have two and three, respectively. The only specimens which 

 have been found were in the London Clay or Lower Eocene of 

 England and are preserved in the British Museum. 



The Eohippus is much better known. It comes from the Lower 

 Eocene of Wyoming and New Mexico, and is very Hke the Hy- 



FIQ. 1.— UPPER AND LOWER TEETH OF " EOHIPPUS," FROM 

 THE LOWER EOCENE OF WYOMING. NATURAL SIZE 



racotheriiim except that the molar teeth have the cusps more 

 clearly fusing into cross-crests, and the last premolar is begin- 

 ning to look like one of the true molars. The forefoot of this 

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

 hindfoot has three complete toes and the splint of another. A 

 specimen of the hindfoot is shown in the series in the A-case and 

 many incomplete specimens, skulls, jaws etc., of several species 

 in the counter-case. 



3 and 4. Protorohippus and Orohippus. Middle Eocene. 

 In these animals the splint of the first digit in the forefoot and 

 the spHnt of the fifth digit of the hindfoot have disappeared, but 

 there are still four complete toes in the fore- and three in the hind- 

 foot. The crests on the molars are a little clearer and the last 

 premolar has become almost like the molars, while the next to 

 the last premolar is beginning to become so. A skeleton of 

 Protorohippus is mounted in the wall-case. It shows an animal 

 of the size of a small dog, and proportioned much like the breed 

 known as the whippet, of which a skeleton has been placed near by 

 for comparison with the Protorohippus skeleton. The Protoro- 

 hippus was found by Dr. J. L. Wortman in 1880 in the Wind 



