THE PREHISTORIC HORSE 



above-referred-to discoveries, the following descriptive information 

 is presented relative to the evolution of the prehistoric horse 

 through several geological periods : 



Eohippus, formerly known as Hyracotherium, existed in the 

 Lower Eocene period. The teeth, short-crowned, were covered 

 with little knobs of enamel. The fore foot had four complete toes 

 and a splint of a fifth, while the hind foot had three toes and a 



Head 



Fore Foot 



HindFoot 



Teeth 



OneToe 



Splints of 



2d and 4th 



digits 



OneToe 



Splints of 

 Zd and 4th 

 digits 



Protohippus 



Mesohippus 



ThreeToes 



Side toes 



not touching 



the ground 



Three Toes 



Sid&~toes 



not touching 



the ground 



Long- 

 Crowned, 

 Cement- 

 covered 



ThreeToes 



Side toes 



touching the 



ground; 

 Splint ofSlhdigit 



Protorohippus 



ThreeToes 



Sidetoes 



touching the 



ground 



Four Toes 



Short- 

 Crowned, 

 without 

 Cement 



Hyracotherium 

 (Eohippus) 



FourToes 

 Splint of 

 1st digit 



ThreeToes 

 Splint of 

 5th digit 



FIG. 2. Comparative drawings of skulls, feet, and teeth of prehistoric horse, 



showing evolutionary development. Reproduced by permission from Guide 



Leaflet No. 9, American Museum of Natural Histor 



splint. The skull suggests a civet rather than a horse. Remains 

 have been found in a number of parts of the world, but more espe- 

 cially in the Bad Lands of the Western states. These are about 

 the size of a cat or fox terrier, and have been termed " dawn 

 horses." Eleven stages of development have been assumed to have 

 taken place from and including this period to the present time. 



Protorohippus and Orohippus are from the Middle Eocene 

 period. Here the splints in the hind feet have disappeared, and 

 the crests on the molars are more apparent. These horses were 



