122 UNnKRHITJ. : 



elements of the limbs fall awa}^ while the axial ones develop, 

 giving more speed and a foot better fitted to the harder turf of 

 the more elevated land. The neck and head are elongating 

 to conform to the increasing height, while the teeth gradually 

 lose their omnivorous characters and become adapted to the 

 tougher grasses of the plains. And so it all goes on through 

 the Tertiary Age. It would appear that the horse develops 

 with the plains until, when we reach the beginning of the 

 Quaternary, we find him one of the most specialized of ani- 

 mals in his adaptation to these plains which have become his 

 natural environment. 



During an expedition sent out by the American Museum 

 of Natural History into Northern Texas in 1899, there was 

 found, among fragments of others, a complete skeleton of one 

 of these Pleistocene horses, which is now set up in this museum, 

 and represents the last of its race in America. There are no 

 features in this skeleton to distinguish it generically from that 

 of existing species. It is somewhat larger than the zebra, 

 with bulging forehead, short neck, rather long body, and 

 short legs. The lateral digits of its ancestors are gone from 

 both front and hind feet, arid there are two rudimentary meta- 

 carpal and two rudimentary metatarsal bones. The dentition 

 is three incisors, one canine, three premolars and three molars 

 on each side above and below, making forty teeth in all. The 

 first of the four premolars of an earlier stage having disap- 

 peared from the lower jaw, its corresponding tooth above has 

 ceased to be functionally developed, and the remaining pre- 

 molars have assumed all of the characters of the true molars. 



It is this horse that before the great ice sheets covered the 

 northern parts of North x'Vmerica and Europe, roamed over 

 the open lands of all the continents except Australia and then, 

 during the Cilacial Period, became extinct in America and 

 later disappeared from the scene in Europe. Here his trail 

 sinks beneath the geological horizon just as the first scratch- 

 ings and chippings of man are appearing abcn'e it. Why, we 

 do not know. It has been assigned to the ice during the 



