298 TOWARDS THE HUMAN FORM 



This seriation is preserved in the Titanotheridse of North 

 America (Lambdotherium, Palceosyops, and Diplacodon of the 

 Eocene), which, with Titanotherium, attained in the Miocene 

 to the size of an Elephant. These animals had four digits on the 

 front and three on the hind feet, and bore on their noses a 

 pair of large protuberances, which doubtless supported horns 

 analogous to those of the Rhinoceros. The Macranchenia 

 and the Proterotheridae had only three digits to each foot. 

 They lived in South America and constituted a series which 

 immediately followed on to the Condylarthra. In another 

 series the carpal and tarsal bones had ceased to be seriated. 

 This series begins in the Eocene with Hyracotherium, an animal 

 about the size of a Fox, which appeared in America, and 

 there evolved into Pachynolophus and Propalceotherium, 

 represented in America by Orohippus, Eohippns of Wasatsch, 

 and Epiphippus of Uriste, which had four digits on the fore 

 and three on the hind limbs. The Lophiodontidse of Europe 

 and of the American Eocene (Lophiodon, Heptodon, Helaletes), 

 the Tapirida?, which differ from them in the character of their 

 molars (Systemodon, Hyrachyus, Tapiravus, of America, and 

 Protapiriis and Tapirus of Europe), all had four digits in front 

 and three behind. But in Palceotherium and Paloplotherium 

 of the Eocene of Europe, many species of which have left their 

 remains in the gypsum of Montmartre, the number of digits on 

 all four feet had already decreased to three, all of which rested 

 on the ground. These animals had the gait of Llamas ; their 

 radius and their fibula were complete, and they had a rudi- 

 mentary fifth metatarsal. Similarly the Rhinoceros, which has 

 survived to our own times, appears first in the Eocene of 

 Wyoming and the Uinta formations as the genus Amynodon, 

 with few exceptions (Acerotherium, Dicer atherium) as a tridactyle 

 animal. 



The reduction of the toes was continued in the series of 

 Equidae, whose molars are marked by a median longitudinal 

 crest. The three toes in this series are still almost equal and 

 touch the ground in Mesohippus of the American Oligocene, 

 whose fibula has begun to be reduced. The median toe becomes 

 prominent in the American Miohippus, which migrated into 

 Europe in the Miocene, where it constituted the genus 

 Anchitherium in the Middle Miocene of France and Germany. 

 This predominance is accentuated, and the lateral toes cease 



