56 THE HORSE. 



absent * In respect to the front teeth, therefore, a 

 very marked amount of specialization has taken 

 place. On the other hand, the cheek teeth are re- 

 tained in full normal numbers — viz., four premolars 

 and three molars on each side above and below, all 

 in contact, and closely resembling each other, except 

 the first, which is much smaller than the rest, and 

 often lost early in life. The others gradually in- 

 crease in size from before backwards up to the 

 penultimate, which is the largest. The upper mo- 

 lars have a very characteristic pattern, admirably 

 adapted for bruising and crushing coarse vegetable 

 substances, and which is clearly a modification of 

 the pattern already seen in the corresponding teeth 

 of Hyracotherium. The lower molars are of simpler 

 form, the two transverse ridges being curved into 

 a crescentic form. In neither case are the deep de- 

 pressions between the ridges filled up with cement, 

 as in the horse. 



The skull is elongated and elevated posteriorly 

 into a transverse occipital crest. It has retained its 

 primitive condition in possessing no post-orbital 

 processes or any separation between the orbits and 

 temporal fossae. The nasal bones are large and 

 stout, co-ossified, and standing out freely above the 



* It should be stated that certain teeth, regarded above as 

 incisors, are considered by some zoologists as modified canines. 



