688 EVOLUTION OF THE HORSE. 



" all about the size of a fox." The name, Eohippus 

 (Horse of the Eocene), implies that its remains were found 

 in Eocene deposits. Hyracotherium, like many of the 

 mammals of the Eocene epoch, inhabited Europe as well 

 as America. The ist digit was absent in all the feet, and 

 the 5th digit was present only in a vestigial form in the 

 hind ones. The bones of the wrist (knee) were becoming 

 interlocked, as in the horse, but the ulna and fibula were 

 still complete and separate, as in Phenacodus. " In the 

 structure of the feet and teeth, the Eohippus unmistakably 

 indicates that the direct ancestral descent of the modern 

 horse had already separated from the other perissodactyles, 

 or odd-toed ungulates " (Marsh). 



The canine teeth were everted (bent outwards) and 

 well developed, the incisors separate and chisel-shaped, 

 and the premolars quite different from the molars. The 

 3rd premolar had three cusps ; and the molars, six 

 cusps. The orbit was incomplete, as in the dog, and the 

 brain was larger than that of Phenacodus. The food of 

 Eohippus appears to have been succulent grasses. 



Protorohippus was about 18 inches high and closely 

 resembled Eohippus, except that it had no vestige of the 

 5th digit in the hind foot, and was more horse-like. 



Orohippus (Pachynolophus, Fig. 643), which was 

 found in America, received its name from Professor 

 Marsh, apparently because he regarded it as the 

 limit (Greek, oros, limit ; and hippos, horse) to which 

 horse-like animals can be traced. Its resemblance to 

 the equine type, though still distant, .was closer than 

 that of its predecessors. The last two premolars had 

 gone over to the molar series. " Orohippus was but 

 little larger than Eohippus, and in most respects was 

 very similar. Several species have been found, but 

 none occur later than the Upper Eocene " (Marsh). 



