16 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 Orohtppus 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.) 
Paleotherium and Paloplotherium 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 Pale@otherium were of large size, equaltoatapir. 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. 
6and 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 Mesohtppus bairdi about the size of a coyote, 
