292 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



characterize these animals. Using the term horses in a 

 broad sense to include all the existing members of the family 

 Equidse, true horses, asses, zebras and quaggas, we find a greater 

 uniformity in the skeleton and teeth than would be expected 



Fig. 147. — Asiatic Wild Horse (Equus przewalskii). — By permission of the 

 N.Y. Zoolog. Soc. 



from the external appearance. The differences in appearance 

 are, however, largely due to colouring, growth of mane and 

 tail and the size of the ears, which leave no record in the skeleton. 



The teeth (Figs. 45, p. 95 ; 154, p. 306) are extremely high- 

 crowned, or hypsodont, and do not form roots till an advanced 

 age ; the incisors have a deep, enamel-lined pit, the ''mark" in 

 the centre of the grinding surface ; the first premolar in each 

 jaw is very small and of no functional importance ; the other 

 premolars have the same pattern as the molars, which is 

 excessively complex in the arrangement of the enamel ridges 

 and the areas of dentine and cement. 



The skull (Fig. 154, p. 306) is long, especially the facial por- 

 tion, the eye-socket (orbit) being shifted behind the teeth, which 



