APES. 445 



enamel covering the grinding surface is finely wrinkled before abra- 

 sion. In the upper jaw both premolars and molars are implanted by- 

 three diverging fangs, two external and one internal ; the anterior ex- 

 ternal fang of the first premolar is the longest and strongest. In the 

 lower jaw the median incisors are a little larger than the lateral ones, 

 in which the outer angle is usually rounded oflf; the crowns of the 

 canines are less robust than those above. The outer part of the 

 first premolar rises to a sub-acute point, from which three ridges 

 descend, one to the fore part of the grinding surface, the other 

 to the back part, and the third to the inner part, which is developed 

 into a slight tubercle. In the second premolar this tubercle rises 

 almost to an equality with the outer one. The first and second 

 true molars have three cusps along the outer curve of the grinding 

 surface, and two upon the inner side, the anterior being the highest. 

 The last molar has two external cusps, and the posterior inner 

 one is almost obsolete. The premolar and molar teeth are each 

 inserted by two strong diverging fangs. The series of grinders forms 

 a straight line in both jaws. 



The dentition of the Chimpanzee (Simla Troglodytes), though 

 in all its most prominent characters strictly Quadrumanous, yet, 

 in the minor particulars in which it differs from that of the Orang, 

 advances towards the human type. In the upper jaw the middle 

 incisors (PI. 118, fig. 1, i) are smaller, the lateral ones larger 

 than those of the Orang ; they are thus more nearly equal to 

 each other ; nevertheless the proportional superiority of the middle 

 pair is greater than in Man. Each incisor has a prominent posterior 

 basal ridge, and the outer angle of the lateral incisors is rounded 

 off", as in the Orang. The diastema between the incisors and canine 

 is narrower than in the Orang. The crown of the canine (ib. c), 

 passing outside the interspace between the lower canine and pre- 

 molar, extends a little below the alveolar border of the under jaw 

 when the mouth is shut ; it is conical, pointed, more compressed 

 than in the Orang, and with a sharper posterior edge ; convex 

 anteriorly, flattened at the posterior half of the outer surface, concave 

 on the corresponding part of the inner surface, which is traversed 

 by a shallow longitudinal impression : a feeble ridge divides this 

 from the convex anterior surface, which bears a linear longitudinal 



