348 LAND MAMMALS IN THE WESTERN HEMISPHERE 



a third mode of development was exemplified by the famyno- 

 donts, in which the canines became large and formidable tusks, 

 a very notable difTerence from all other rhinoceroses whatever. 



In jMeiamynodon the incisors were not enlarged, but were 

 unreduced and functional ; the upper canine was a short, 

 heavy tusk, obliquely truncated by the abrasion of the lower 

 tusk, which was very large. Another striking difference from 

 all the other groups of rhinoceroses was the reduction of the 

 premolar teeth, which, instead of equalling the molars in size, 

 were much smaller and were diminished to three in the upper, 

 two in the lower jaw. The molars were of the characteristic 

 rhinoceros-pattern, but were very narrow, especially the inferior 

 ones, in which the enamel did not surround the whole crown, as 

 it normally does, but was lacking along vertical bands, where 

 the dentine formed the surface. The skull was extremely pecul- 

 iar and, with its very long and high sagittal crest and immensely 

 expanded and heavy zygomatic arches, had a surprising like- 

 ness to the skull of some great beast of prey. The face was 

 very much shortened and the skull depressed, so that the 

 head was remarkably low, broad and flat, proportions which 

 did not recur in any other group of rhinoceroses. The neck 

 was short, the body very long and very massive, as is shown 

 by the long and strongly arched ribs. The limbs were short 

 and stout and the feet quite primitive in character, the front 

 foot retaining four fully developed and functional digits. 

 No other perissodactyls of the middle White River beds, 

 except the flophiodonts and tapirs, had more than three digits 

 in the manus, and thus ^Metamyodon was a belated exception 

 to the general rule. 



The Uinta member of this series was ]Amynodon, a similar 

 but smaller and lighter animal. The canine tusks were of 

 more moderate size and none of the premolars had been lost, 

 but were considerably smaller than the molars, and the last 

 two had assumed the molar-pattern. The face was not conspic- 

 uously shortened and the zygomatic arches of the skull were 



