378 HISTORICAL GEOLOGY. 



except that the fifth rudimentary toe is dropped. These 

 animals were about the size of a fox. 



FIG. 340. Tinoceras ingens. (After Marsh.) 



Miocene. The Eocene lake-deposits are in the Pla- 

 teau region, the Miocene and Pliocene are in the Plains 

 and Basin region. The first thing to be noted here is the 

 complete change of species. It is worthy of note that in 

 the Miocene many existing families (not species), such as 

 the rhinoceros family,, the camel family, the deer family, 

 the dog family, and the cat family commenced to exist. 

 Among the many forms which occur here we can only 

 mention the most remarkable. In this respect, certainly, 

 the Brontothere stands first. This animal was still larger 

 than the tinoceras, and connects the latter with the 

 rhinoceros. The peculiar saddle-shaped head was three 

 feet long. It had only three toes behind, like the rhi- 

 noceros, but four in front. 



In the Miocene the horse family is represented by the 

 Mesohippus and Mwhippus. These had three toes on 

 the hind and the fore foot, and were about the size of a 

 sheep. True tridactyl horses commence here. 



