146 THE MAMMALIA. 



dentition show very little modification, and the 

 formation of its foot has remained very faithful to 

 the primary type from the Eocene, the lineal 

 descendants of which, unfortunately, cannot he 

 pointed out singly. The Eocene animals with 

 tuberculate teeth, and likewise the Early Tertiary 

 ancestors of the Ruminants, had to dwell prin- 



FIG. 19. First Upper Molar of the Hippopotamus, to the right. 

 But little worn off. 



cipally in waters and on marshy ground. Their 

 descendants adapted llk-msi'lves gradually to life 

 on dry ground, and this is connected with the 

 advantageous reduction of the toes. The Hippopo- 

 tamus family has taken an opposite course, from 

 being an animal that liked the marshy soil of 

 the primeval forests, it has beeume almost an 



