134 Life of Upper Lake Region. 



ful increase in the variety of its fossil forms. 

 The one that attracts our attention most from 

 the frequency of its occurrence and beauty of 

 its fossil forms is that of the Hipparion. As 

 it occupies a midway position between the 

 Anchitherium and living horse, if we com- 

 pare the Anchitherium with the Hipparion we 

 shall have the amount of change through 

 which the horse passed from the Miocene to 

 the Pliocene age. And carrying the work 

 further if we compare the Hipparion with the 

 present horse we shall have the amount of 

 change through which the horse has passed 

 from the Pliocene to the present. Let us 

 first compare the horse of the Miocene with 

 that of the Pliocene. We find the simpler 

 teeth of the Anchitherium ha^e in the Hip- 

 parion taken on a more complex form in the 

 prisms of their enamel (see Plate XXV), and 

 that the molar teeth of the Anchitherium were, 

 through a large part of their trunks divided 

 into spreading roots, the body part of the 

 tooth remaining short, while in Hipparion 

 the molar teeth have small short roots and 



