28 THE HORSE AND ITS RELATIVES 



dental series of the ox and its relatives, in which, 

 however, the lower canines have become approxi- 

 mated to the incisors, with which they form a regular 

 series of spatulate-crowned teeth. In the upper 

 jaw of the ox tribe specialisation has been carried to 

 a much greater extent than in the horse, the canines 

 and incisors having completely disappeared, and 

 being replaced by a hard pad which takes the bite 

 of the lower front teeth. In consequence of the 

 retention of upper as well as lower front teeth, 

 a horse is apparently able to graze closer than 

 an ox. 



From the existence of the aforesaid long gap 

 between the front and the cheek teeth in both the 

 horse and the ox and their respective relatives, it 

 would seem that such an arrangement is the one best 

 suited for grazing or browsing animals ; and it is not 

 improbably for the purpose of affording room for 

 the play of the large tongue, which takes an impor- 

 tant share in the action of grazing. 



The incisors of the horse, of which those of 

 the lower jaw have somewhat less distinctly spatu- 

 late crowns than their representatives in the ox, 

 present a relatively complex type, met with among 

 no other living mammals outside the Equidcs. 

 In place of having simple conical crowns when they 

 first emerge in an unworn condition from the gum, 

 the incisor teeth of the horse have a kind of 

 pit, or pocket, at the summit, which penetrates far 



