ITS ANCESTOBS AND RELATIONS 



23 



The characters of the teeth, as well as their number, are 

 of a generalised type. The incisors are small, subequal, 

 and with cutting 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 

 defined from the latter by their simpler structure. Their 

 crowns are all extremely brachydont, or short from above 

 downwards, a character met with in all primitive forms. 

 The true molars belong to the simplest, or 1 bunodont ' 1 

 type, having four principal rounded cusps on the grind- 

 ing surface of each, with smaller cusps between, making 

 six altogether. (See fig. 3, A, page 30.) 



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 continuous 

 with the temporal fossaD on the side of the skull, as 

 in all primitive forms. The vertebral column is said to 

 consist of seven cervical, fourteen or fifteen thoracic, six 

 or seven lumbar, and three to five sacral vertebrae. The 

 tail is long and tapering, much longer than in any exist- 

 ing ungulate, as it must have reached quite to the ground 



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 condition) the primitive formula. 

 1 From the Greek bounos, a hill or mound. 



