VERTEBRATA: MAMMALIA. 



701 



prising the Asses and Zebras. Many authorities, however, 

 place all the existing forms under the single genus Equus. 



The genus Equus is distinguished by the fact that the 

 animal is not banded, and has no dorsal line ; both the fore 

 and hind legs have warts, and the tail is hairy throughout. 

 The genus appears to contain no more than one well-marked 



Fig. 396. Grinding-surfaces of the last praemolar and of the three true molars 

 of the upper jaw of the Horse. (After Cuvier.) 



species, if the Asses be excluded, and as far as living forms are 

 concerned namely, the Equus caballus. From this single 

 species appear to have descended all the innumerable varieties 

 of horses which are employed by man. The native country 

 of the horse appears to have been Central Asia, but all the 

 known wild individuals of the present day appear to be de- 

 scendants of domestic breeds. 



The Ass (Asinus vulgaris) is characterised by the fact that 

 there is always a distinct dorsal line, and the body is more 

 or less banded; the fore-legs alone have warts, and the tail 

 has a tuft of long hair at its extremity. The Ass is probably a 

 native either of Northern Africa, or of South-western Asia, and 

 it has been supposed to be the descendant either of the "Djig- 

 getai" (Asinus hemionus\ or the "Onager" (Asinus onager), both 

 wild existing species : though a more probable stock for it is 

 to be found in the Asinus tceniopus of Abyssinia. According 

 to Lenormant, the Ass was domesticated in Egypt at the very 

 earliest periods of its history, long before the introduction of 

 the Horse ; and it may therefore be the descendant of a wild 

 African form. The striped and banded asses are known as 

 Zebras and Quaggas, and are distributed over the greater part 

 of Africa. Several genera (Anchitherium, Hipparion, Orohip- 

 pus, Miohippus, Pliohippus, &c.) have been founded upon the 



