LIFE IN TERTIARY TIMES 295 



last, each cuneiform supporting one toe and the cuboid two. 

 This serial arrangement is characteristic of a group of mammals 

 which did not survive the Eocene Period, and to which Cope 

 gave the name of Condylarthra. Their principal representa- 

 tives are mainly, if not exclusively, American : Periptychns, 

 still plantigrade, and Phenacodus, semi-digitigrade, about the 

 size of a large sheep. Among the large Ungulates, all of them 

 Eocene, this seriation had already become modified ; they were 

 still semi-plantigrade, and consequently provided with all 

 five toes. Cope grouped them together as Amblypoda. In their 

 feet, the bones of the second row of the carpus slightly over- 

 ride the first, and the metacarpals alternate with them 

 regularly in such a way as to support themselves between two of 

 them and thus maintain their union. 



Representatives of this order particularly well distributed 

 in North America are Pantolambda, Coryphodon, Loxohphodon 

 with a skull more than a metre in length, and Dinoceras, 

 about the size of a Hippopotamus, powerfully armed, like the 

 others, with horns and canines, of which we shall speak later. 

 The short feet still have four to five toes, all of which rest on 

 the ground in Mceritherium and Palceomastodon, in various 

 precursors of the Elephants, and in the Elephants themselves. 

 These have all been grouped together in the order of Barypoda, 

 in which the dentition undergoes considerable reduction. 

 We see, finally, a gradual diminution in the number of toes, 

 coinciding with important modifications in dentition in the 

 heavy animals, with serially arranged tarsus or carpus, as in 

 those Condylarthra that Burmeister has included in the order 

 of Toxodontia. Homalodontherium and Prototypotherium are 

 still pentadactyle, but there are only four digits in the hind 

 feet of Typotherium, and this reduction has also taken place 

 in the fore feet of Toxodon. Finally, in Hyrax, an animal of 

 the size of a Rabbit, our present-day representative of the 

 whole order, there are only three digits in the hind and four in 

 the front foot. This brings us to those orders in which the 

 straightening of the foot having reached the maximum, the 

 animal only rests the extremity of its longest digit upon the 

 ground. 



If the third digit is sufficiently longer than the others, it 

 supports the whole weight of the body. Ungulates with feet 

 so constructed are called Perissodactyla. If the third and 



