ITS ANCESTORS AND RELATIONS. 35 



cations of which the names Menodus, Titanotherium, 

 Megacerops, Brontotherium, and Symborodon have been 

 given. They were of gigantic size, with a large head, 

 haying on the face a pair of stout, diverging, osseous 

 protuberances, like the horn-cores of ruminants. 

 Their fore-feet had four and their hind feet had 

 three short stout toes. Also, out of the line of descent 

 of any existing Perissodactyles was the remarkable 

 Macrauchenia, a very specialized form, which existed 

 in South America, apparently to Pliocene times, and 

 then entirely disappeared from a world in which the 

 conditions necessary for its well-being no longer ex- 

 isted, unless indeed we may suppose that the life-of a 

 species, like that of an individual, comes to an end by 

 virtue of some inherent tendency which is one of the 

 essential attributes of its existence. Leaving these 

 and numerous other collateral branches which have 

 left no representatives, we may pass to the third ex- 

 isting division, the most important in regard to the 

 present subject. 



Allied to Palaeotherium, but probably more on 

 the direct line of descent between Hyracotherium 

 and the forms to be mentioned presently, was a small 

 animal to which the name of PalaplotJierium has been 

 given, of which numerous teeth and bones have been 

 found in the beds of Upper Eocene age at Hord- 

 well in Hampshire, in the Isle of Wight, and in va- 



