THE TEETH OF MAMMALS 165 



as the true molars. The upper molar crowns are 

 cubical and large. The grinding face presents a 

 peculiar pattern which is distinctive of all vari- 

 eties of the genus Equus, both living and extinct. 

 The molars are rather of an archaic pattern, and 

 not so complicated as in the Euminants. The 

 characteristic crescents of the lower molar ridges 

 are much like those of the Rhinoceros. The 

 phytogeny of the horse has been well made out, 

 and the pattern of the teeth has played an impor- 



Fig. 70. — Roentgenogram of mandible of a young horse. (By Dr. 

 E. H. Skinner.) 



tant part in this most interesting scientific tri- 

 umph. The teeth are hypsoclont as the crown 

 exceeds the length of the root and the teeth erupt 

 farther as the crown is worn off (Figs. 70 

 and 71). 



