ORDER UNGULATA. 



I 4 0: 



signis, the ridges of the molars (fig. 1280 1 ) become more numerous, and 

 somewhat higher : while the intervening valleys are more or less com- 

 pletely filled with cement. The number of ridges in the cheek-teeth 



of this species may be represented by the formula Mm. 



M. 



(7-s; 



-8). (9-1 1) 



2-5- (7-9)' 

 Allied species are E. bombifrons and E. 



(7-10). (8-12). (9-13)' 

 ganesa, which are found in the Pliocene of India and the countries to the 

 eastward as far as Japan. 



In the second, or Elephantine, group, the specialisation of the 

 molars becomes greater ; in all the species the ridges are so tall 

 that they assume the appearance of plates, but there is great varia- 



Fig. 1280. — Elephas insignis. Vertical and longitudinal section of the third left upper true 

 molar ; from the Pliocene of the Siwalik Hills. One-third natural size, a, Cement ; b, Enamel ; 

 c. Dentine. (After Falconer and Cautley. ) 



tion in respect to their height and number ; those of the less special- 

 ised forms not being more numerous than in E. insignis. The 

 cement always completely fills the interspaces between the ridges, 

 and in the higher forms these interspaces are extremely narrow. 



One of the least specialised members of this group is Elephas pi ani- 

 frons, from the Pliocene of Northern India, of which the section of an 

 upper molar is represented in fig. 1281. In the teeth of this species the 

 number of the ridges is nearly the same as in E. insignis j but, as will 

 be seen from the figure, the ridges have become much taller and thinner, 

 and the valleys are completely rilled up with cement. It results from this 

 structure that when the crown of the tooth has become well worn (as in 

 the anterior half of fig. 1282), its grinding aspect will present a nearly flat 

 surface marked by a series of transversely elongated raised disks of 

 enamel, each enclosing an islet of dentine. This structure, which is still 

 better exemplified in the more-worn molar of the closely allied E. meri- 

 dionalis fig. 12S3 . of the Upper Pliocene of Tuscany and the Norfolk 

 ,; Forest-bed. - '' is admirably adapted for the attrition of vegetable matter 

 owing to the inequalities produced on the surface, due to the variation in 



1 In this figure, as well as 111 fig. 1281, the tooth is turned the wrong way 

 upwards. 



