24 THE HORSE. 



met with have been derived.* The characters of the 

 teeth, as well as their number, are of a generalized 

 type. The incisors are small, subequal, and with cut- 

 ting edges, and are set in a semicircular line. The 

 canines are, however, distinctly differentiated from 

 the other teeth, isolated from the incisors in front 

 and from the premolars behind, and are moderately 

 strong, conical, and pointed. The premolars and 

 molars are in a contiguous series, and the former are 

 distinctly denned from the latter by their simpler 

 structure. Their crowns are all extremely brachy- 

 dont, or short from above downwards, a character 

 met with in all primitive forms. The true molars 

 belong to the simplest, or " bunodont " t type, having 

 four principal rounded cusps on the grinding surface 

 of each, with smaller cusps between, making six al- 

 together. (See Fig. 3, A, page 31.) 



The head is of small size compared with the body 

 generally. The orbits, or cavities for the eyes, are 

 not completed by bone behind, but are widely con- 

 tinuous with the temporal fossae on the side of 

 the skull, as in all primitive forms. The vertebral 



* In the pig and a few insectivora alone among existing 

 mammals is this number retained. In all others the total 

 number of teeth falls short of forty-four, although, as we 

 shall see, some horses still retain (as an exceptional condi- 

 tion) the primitive formula. 



t From the Greek bounos, a hill or mound. 



