320 



MAMMALIA. 



RECENT. 



EQUUS. 



PLIOCENE. 



PLIOHIPPUS. 



MIO-PLIOCENE. 



PROTOHIPPUS. 

 (Hipparion.} 



MIOCENE. 



MlOHIPPUS. 



(Anchitherium. ) 



MESOHIPPUS. 



EOCENE. 



OROHIPPUS. 



FIG. 182. 



Diagram illustrating the Evolution of the Limbs and Molars in the Equine Ungu- 

 lata. A, fore foot; B, hind foot; c, fore arm; D, shin; E, worn upper molar, 

 side- and crown- views; F, worn lower molar, crown-view. (After Marsh.) 



