32 



PLEISTOCENE MAMMALIA. 



Upper Dentition. 



The premolars and molars form a continuous series (PI. II, fig. 1) ; all the 

 members of which are similar in character, but the premolars are little more 

 than half the size of the molars. The character of the grinding surface is better 

 realized from figures than from descriptions, but its peculiar irregularity depends 

 primarily on a dorsal infolding of the enamel, which after wear forms an 

 irregular depression sometimes partly occupied by cement and surrounded by an 

 enamel rim. External to this rim is the dentine forming the bulk of the tooth, while 

 finally the prominent outer border consists of enamel. In the premolars the infold 



a. 



Fig. 13. — Anterior end of mandible with incisor and canine teeth. A Left side view; B seen from above ; half 

 natural size. From Mullingar (Nat. Mus., Dublin), a, mental foramen for passage of a branch of the 5th nerve. 



of enamel has the posterior portion nearly or completely isolated from the remainder 

 according to the state of wear of the tooth. In the molar teeth a sharp infold of 

 enamel from the inner side greatly modifies the whole grinding surface, and gives the 

 dorsal infold the character of a double crescent. The molar teeth have four roots, 

 the premolars two on the inner, but one on the outer side. 



Lower Dentition. 



The three incisors and the incisiform canine have long tapering roots and expanded 

 chisel-like blades, which together form a continuous cutting edge. The upper surface 

 of the blade is marked by a depression. The teeth project conspicuously forward, 



