154 



UNGULATA 



ORDER VII 



with pits. Canines present in both sexes. Cheek teeth prismatic, but only- 

 half as deep as in the horse. .First superior premolar small, early deciduous ; 



Fig. 209. 



Merychippus sejunctus Cope sp. Lower Pliocene, Colorado. Lateral aspect of skull and lower jaw, 

 and palatal aspect of skull. 1/3. (After Cope.) 



second premolar broadly triangular, somewhat larger than the other cheek 

 teeth. Protocone forming an isolated cylindrical pillar. Enamel of the valleys 

 strongly wrinkled ; cement very abundant. Inferior molars consisting of two 



crescents, which through their union 

 form one longitudinal double 

 column ; this through wear is 

 represented by large plications. 

 The internal horn of the hypolophid 

 also develops into an oblong column, 

 which sometimes comes in contact 

 with the metastylid. The milk 

 teeth resemble the succeeding pre- 



ProtoUppux mirabilis Leidy sp. Lower Pliocene, molarS, yet are SOmewhat mOre 

 Nebraska. .J, Upper milk-molar. B, Lower molar, i/i. 1^1 j •j.i, ^ 



(After Leidy.) elongate, lower and with longer 



roots. The inferior milk teeth are 

 characterised by a very small pillar in the median transverse valley of the 

 external side ; the superior milk teeth are narrower than their successors and 

 less copiously filled with cement. Skull somewhat smaller and lower than 

 in the horse. In front of the lachrymal is a deep fossa bounded below by 

 the broad maxillary crest. Extremities tridactyl, the median metapodial 



Fio. 210. 



