37& 



SYSTEMATIC ZOOLOGY 



The horses all belong to the genus Equus, and, scientifically- 

 considered, include the asses and the zebras (Fig. 370). They 

 have a soft, hairy skin, with a longer or shorter mane on the 

 dorsal side of the neck, and either a bushy tail, as in the domestic 

 horse and the quagga of South Africa, or a smooth tail with a 

 brush near the tip, as in the ass and the zebra. Only the 



FIG. 370. Equus zebra, the /obi a. ( From a photograph provided by the American Museum 



of Natural History.) 



third digit is developed, but the second and fourth are repre- 

 sented by the " splint " bones of the skeleton, although these are 

 not normally apparent externally. The various species will in- 

 terbreed freely, but the offspring are not generally fertile. The 

 mule is the offspring of the mare and the male ass ; the hinny 

 of the stallion and the female ass. The horse is found in its 

 natural wild state to-day only in Asia and Africa, although fossil 



