156 



UNGULATA 



ORDER VII 



milk teeth is elliptical in cross-section, the bones of the extremities, especially 

 the metapodials, are more slender, and the lateral digits are more strongly 

 reduced. Neohipparion is probably confined to the Upper Miocene. N. 

 occidentale Leidy, Nebraska. JSf. whitneyi Gidley, South Dakota ; TV. speciosum 

 and N. gratum Leidy, Nebraska. 



Hippidium Owen (Rhinippus Burmeister). Dentition very similar to that 

 of Protohippus, but without wrinkling of the enamel, yet the superior cheek 

 teeth are strongly curved, shorter than in Uquus, with separate roots closed 

 below ; the two internal tubercles subequal in size, oval, united with the 

 crescentic intermediate pillars. Narial aperture extending back to above the 

 last molar; nasal bones unusually long, projecting freely. Metapodials 

 stouter and shorter than in the horse ; lateral splint bones reaching to just 

 above the mid-length of the median metapodial. 

 Lower Pampas formation ; Argentina, Brazil and 

 Bolivia. H. (Eqims) neogaeum and H. principale 

 Lund sp. Onohippidium Moreno, with long deep pit 

 in front of the lachrymal. Pleistocene ; Argentina. 

 Equus Linn. (Figs. 211, A ; 214). Incisors with 

 pit. Cheek teeth much deepened, prismatic, in the 

 young open below, without separate roots. First 

 premolar in the upper jaw very small, peg-shaped, 

 rarely present. In the superior molars, the infolding 

 of the enamel of the intermediate cusps less elabor- 

 ately crimped than in Hipparion. Both internal 

 cones connected with the intermediate tubercles by 

 a narrow neck ; protocone considerably more robust 

 than hypocone and usually elliptical. Cement very 

 copious. Inferior cheek teeth as in Protohipptis, but 

 much higher crowns. In the carpus, the trapezium 

 and fifth metacarpal are absent. The lateral meta- 

 podials of both manus and pes are represented by 

 styloid splint bones without digits ; however, ab- 

 normal individuals are sometimes found in which 

 the splint bones are well developed and bear three phalanges, as in Hipparion. 

 On the other hand, the cases described as atavistic by Marsh are merely 

 abnormalities, like the supernumerary sixth digit in man. They are so 

 proved to be by the presence of two ossa magna. 



The genus Equus had its inception in India, in the Lower Pliocene 1 

 (Siwalik beds), and in China, originating in E. sivalensis Falconer ; in 

 Europe, in the Upper Pliocene, in E. stenonis Cocchi, also in the oldest 

 Pleistocene of Mosbach, followed by E. sUssenlornensis AViist. In the 

 Pleistocene of India it is represented by E. namadicus Falconer. In the 

 later Pleistocene (Diluvium) throughout Europe, northern Asia, and northern 

 Africa, E. caballus Linn, is exceedingly widespread, while the Dzeggetai, E. 

 hemiontis, only occasionally occurs, and the existence of the ass, E. asinus, 

 remains doubtful. In North America, the genus Equus first appears in the 

 so-called " Equus beds " of the western and southern states, as well as Mexico, 

 and has become differentiated into a considerable number of species in the 

 Lower Pleistocene ; E. intennedius Gidley. It continued on into the Middle 

 Pleistocene; E. compUcatus Leidy, E. crenidens Cope, E. scotti Gidley, E. 



Fig. 214. 



Pleisto- 



Eqwis caballus Linn 

 cene and Recent. A, Upper molar, 

 showing inner column (ft). B, 

 Lower molar, i/i. 



