HISTORY OP THE PERISSODACTYLA 315 



the eyes, and must clearly be regarded as incipient stages of 

 the "horns" which were subsequently to become so long and 

 prominent. Instead of being broad on top as it was in the 

 White River genera, the cranium carried a high ridge of bone, 

 the sagittal crest, which served for the attachment on each 

 side of the great temporal muscle, one of the most important 

 of the muscles of mastication. The trunk was less massive 

 and the limbs were lighter than in the Oligocene genera, but 

 the number of digits was the same, four in the front foot and 

 three in the hind, and the hoofs were much better developed, 

 serving actually to carry the weight and not being mere ex- 

 crescences upon the periphery of a pad. Aside from the pro- 

 boscis, which lends such a characteristic appearance to the 

 existing tapirs, the ftitanotheres of the Bridger must have 

 looked much Uke tapirs, and in early days, when the mutual 

 relationships had not been satisfactorily determined, they were 

 frequently described as "tapiroid." The term is unobjection- 

 able in so far as it is understood that a merely superficial like- 

 ness is impUed, not any real relationship other than that which 

 unites all the perissodactyl families. 



As noted above, the phyla of the ftitanotheres were much 

 more numerous in the later than in the earlier part of the 

 Bridger stage, when they were reduced to two. In the still 

 older Wind River stage these two united into one. The Wind 

 River animals (fEotitanops) were similar, but much smaller, 

 and occurred in incomparably less variety and abundance. 

 Indeed, one of the most striking differences between the Wind 

 River and the Bridger faunas consists in the great increase and 

 diversification of the ftitanotheres in the latter. There was, 

 it is true, a second phylum of the family in the Wind River, 

 represented by the genus ^Lambdotherium, but this was a short- 

 lived series, which left no descendants in the Bridger or sub- 

 sequent formations. These were the smallest known members 

 of the family and were light, slender-limbed animals, a very 

 notable difference from the others. 



