136 THE STRUCTURE OF THE HORSE. 



at either extremity narrow off anteriorly and pos- 

 teriorly, but the four middle ones are almost iden- 

 tical. The pattern of these teeth resembles essen- 

 tially that of most of the other Perissodactyles. They 

 consist mainly of two crescents, one placed in front 

 of the other, with their convexities outwards $ but it 

 is peculiar to the Equities, to have the inner ends of 

 the crescents complicated by the addition of columns 

 or lobes, which add considerably to the intricacy of 

 the pattern exposed when the tooth is worn. The 

 extremely hypsodont condition and the quantity 

 of cement which everywhere overlays the enamel 

 and fills in the interstices of the foldings are also 

 special characters of this group, which they share 

 only with the Elasmotlierium among the Rhinocero- 

 tida?. 



The surfaces of the upper and lower molars in 

 wearing against each other do not come in contact 

 in a plane horizontal to the long axis of the tooth, 

 but in one slanting from without upwards, the wear 

 being greatest on the inner side of the upper teeth 

 and the outer side of the lower teeth. 



The roots of the molars are short, and in the up- 

 per ones four in number, except in the first and last, 

 which have only three. In the lower teeth there are 

 two, one anterior and one posterior, in position. 

 After they are fiilly formed, the tooth does not con- 



