THE HEAD AND NEC K 



127 



width from side to side, and present quite a different 

 pattern. As in the upper series, those placed at either 

 extremity narrow off anteriorly and posteriorly, but the 

 four middle ones are almost identical. The pattern of 

 these teeth resembles essentially 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 Equidce 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 JElasmo- 

 t 'he riii, n among the Rhinocerotida3. 



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 slant- 

 ing 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 upper 

 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 

 fully formed, the tooth does not continue to grow, but 



