1 6 EVOLUTION OF THE HORSE 



River Badlands of Wyoming, and was described by Professor 

 Cope and others under the name of the " Four-Toed Horse." 



Of Orohippus we have only parts of jaws and teeth. A 

 specimen of the forefoot is exhibited in the Museum of Yale 

 University. 



5. Epihippus. Upper Eocene. Of this stage of the evolu- 

 tion of the Horse only incomplete specimens have been found. 

 The molar teeth have the once round cusps almost completely 

 converted into crescents and crests, while another tooth of the 

 premolar series has become like the molars. The toes are still four 

 in the forefoot and three in the hindfoot, but the central toe in 

 each foot is becoming much larger than the side toes, a feature 

 which may be seen in the hindfoot shown in the series in the case. 

 (This species happens to be somewhat smaller than those found 

 in the Middle Eocene stage, but no doubt there were others of 

 larger size living at the same time.) 



Palceotherium and Paloploiherium of the Upper Eocene of 

 Europe form a side branch of the Horse line. They were very 

 abundant in Europe, but have not been found in the New World. 

 On each foot they had three toes of nearly equal size, and the 

 teeth show a rather peculiar pattern. One of these animals was 

 thought by Professor Huxley to be a direct ancestor of the Horse, 

 but it now is considered to be merely a collateral relative. Some 

 species of PalcEotherium were of large size, equal to a tapir. They 

 were first described in the year 1804 by the celebrated Baron 

 Cuvier from remains found in the gypsum quarries of Mont- 

 martre, Paris. A large series of skulls, jaws, foot -bones etc., 

 from the Upper Eocene of France, is exhibited in one of the 

 counter-cases. 



6 and 7. Mesohippus. Oligocene (White River Formation). 

 In this stage there are three toes on each foot, a splint represent- 

 ing the fifth digit of the forefoot. of the Eocene ancestors. The 

 middle toe is now much larger than the side toes, which bear very 

 little of the weight of the animal. Three of the premolars have 

 now become entirely like the molar teeth, the crests on the 

 crown are completely formed, and the outside crest in the upper 

 molars has taken the shape of two crescents. In the Middle Oli- 

 gocene is found Mesohippus bairdi about the size of a coyote, 



