202 



THE MAMMALIA. 



which land-bridges this migration took place ; all 

 that can be done meanwhile, is to trace the line 

 of the descendants of the Palaeotheridae, which, it 

 seems, soon came to an end in South America, but 

 became vi'i numerously and continuously de- 



FIG. 35. Palapotherium. Hipparion. Horse (after Owen). 

 p, First premolar ; m, first molar. 



veloped in North America ; and in tracing this line 

 we must do so independently of those branches 

 which run parallel with them in Europe and Asia. 

 Palaeotherium is a distinctly three-hoofed animal. 

 Certainly the middle toe is somewhat larger than 



