MAMMALS. 



395 



In the horses (Equid^) the dentition is z|, c ^, / | to J, m | : there are 

 from four to one toes on the fore feet, three to one on the hind feet. In 

 Hyracothe7'iuin {Eo/iippiis) the toes are four and three on the fore and hind 

 feet respectively ; eocene. Palceoiherium, eocene and miocene of both hemi- 

 spheres, with three toes. Mesohippus, miocene. In Hipparion and Protohip- 

 pus toes z and 4 reduced so as not to reach the ground, but furnished with 

 hoofs ; pliocene. Equiis, the existing horses and asses, has toes 2 and 4 re- 

 duced to metacarpal splint bones without phalanges. The genus appears in 

 the Indian miocene and a little later in North America. The existing species, 

 including the asses and zebras, all belong to the old world. The Proto- 

 THERiD^, with tridactyl feet and incisors \, range through South American 

 tertiary, as do the Macraucheniid/e with the incisors |, and with no dias- 

 tema in the jaws. 



Tapirid/e, with four toes on the fore feet, three on the hind (Fig. 348), 

 range from the eocene to the present time. Lophodon, Isectolophiis, eocene. 



Fig. 366. Sumatran rhinoceros, Ceratorhinus sumatrensis, from Liitken. 



Tapirus arises in the pliocene of Europe, from which have differentiated the 

 tapirs of India and tropical America, the genus dying out in Europe in the 

 pliocene. The existing species are of middle size, and live usually in woods 

 or swampy places. The Rhinocerid/e, or rhinoceroses, have three or four 

 toes on the fore feet, the hind feet tridactyl, the teeth i \ \o ^, c \ or ^, p 

 4 to ft. m f • Some of the extinct forms were without horns, some had one 

 horn and some had two, either one behind the other, as in the existing two- 

 horned species, or as in DiccratJierium, from the miocene of Oregon, the two 

 horns were placed side by side. HyracJiius and Hyracodoii, from the Ameri- 

 can eocene and miocene, were hornless, as was Aceratherimn of the oligocene 

 and miocene, the least differentiated of the true rhinoceroses. The living 

 species are distributed in Ceratorhinus, two horns, from Asia; Atelodus^ 

 two horns, from Africa ; and Rhinoceros, a single horn. 



