PLEISTOCENE EQUIDA£. 693 



caused equine extinction throughout America, must have 

 ceased to act. According to Wallace {Island Life), the 

 camel tribe made a similar migration from America into 

 Asia, over the now-submerged land which had formerly 

 united the two continents. There is no evidence to 

 show that asses or zebras were evolved in America. 



In horses, asses and zebras, the splint bones, ulna 

 and fibula are shorter, and the crowns of the molars 

 and of the molar-like premolars are longer than those 

 of Pliohippus. The carpus (knee) is firmly interlocked, 

 the incisors are closer together, the canines are smaller, 

 and the ist premolar is in a vestigial condition, 

 although, as observed by Professor Ewart, it is present 

 in the embryo. He has also shown that it is sometimes 

 as large in zebras, as it was in Protohippus. The length- 

 ening of the crowns of the molars and of the molar-like 

 premolars shows that the gradual adoption of a harder 

 form of herbage as a food, was a well-marked factor 

 in the evolution of the horse. 



From Phenacodus to the horse of to-day, the 3rd digit 

 has remained the principal one of both fore and hind 

 limbs. It is interesting to note that the digits and 

 phalanges of the fore legs have a less tendency to decrease 

 in number than those of the hind limbs, evidently because 

 their functions are more numerous. In man, the toes 

 are smaller than the fingers, and are less mobile. Occa- 

 sionally in the little toe, as already stated, two of 

 the phalanges coalesce ; although, in the little finger, all 

 these phalanges remain separate. In the case of the 

 re-appearance of the 2nd (as in Fig. 634) and 4th digits 

 in the horse, the fore feet are more frequently supple- 

 mented in this way than the hind ones. 



Equus stenonis is a name which has been given to a 

 group of horse-like animals that inhabited Europe during 

 the Pliocene and Pleistocene periods. Their remains, chiefly 

 teeth, have been found principally in Algeria, France, 

 Switzerland, Italy and England. The study of their teeth 



