020 



TEETH. 



with, and contributes to, the straight line 

 which the canine and premolars form with 

 the true molars. 



The true molars (fg. 586., m. l,w.2, m. 3) are 

 quadricuspid, relatively larger in comparison 

 with the bicuspids than in the Orang. In the 

 first and second molars of both species of 

 Chimpanzee a low ridge connects the antero- 

 internal with the postero-external cusp, cross- 

 ing the crown obliquely, as in Man. There 

 is a feeble indication of the same ridge in the 

 unworn molars of the Orang ; but the four 

 principal cusps are much less distinct, and 

 the whole grinding surface is flatter and more 

 wrinkled than in the Chimpanzee. In the 

 Troglodytes niger the last molar is the smallest, 

 owing to the inferior development of the two 

 hinder cusps, and the oblique connecting 

 ridge is feebly marked. In the Troglodytes 

 Gorilla this ridge is as well developed as in 

 the other molars, but is more transverse in 

 position ; and the crown of m. 3 is equal in 

 size to that of m. 1 or m. 2, having the pos- 

 terior outer cusp, and particularly the pos- 

 terior inner cusp, more distinctly developed 

 than in the Troglodytes niger. The repe- 

 tition of the strong sigmoid curves which 

 the unworn prominences of the first and se- 

 cond true molars present in Man, is a very 

 significant indication of the near affinity of 

 the Chimpanzee as compared with the ap- 

 proach made by the Orangs or any of the 

 inferior Quadrumana, in which the four cusps 

 of the true molars rise distinct and indepen- 

 dently of each other. A low ridge girts the 

 base of the antero-internal cusp of each of 

 the upper true molars in the male Chimpan- 

 zee: it is less marked in the female. The 

 premolars as well as molars are severally im- 

 planted by one internal and two external fangs, 

 diverging but curving towards each other at 

 their ends as if grasping the substance of the 

 jaw. I have found the two outer fangs of 

 the second premolar connate in one female 

 specimen of the Troglodytes niger. In no 

 variety of the human species are the premo- 

 lars normally implanted by three fangs ; at 

 most the root is bifid, and the outer and inner 

 divisions of the root are commonly connate. 

 It is only in the black varieties, and more 

 particularly that race inhabiting Australia, that 



I have found the wisdom tooth, m. 3, with 

 three fangs as a general rule ; and the two 

 outer ones are more or less confluent. 



In the lower jaw of the great Chimpanzee 

 the lateral incisors are broader than the 

 middle ones, although they are smaller rela- 

 tively than in the Troglodytes niger; they are 

 larger and less vertically implanted than in 

 Man. The lower canines are two inches and 

 a half in length, including the root ; the 

 enamelled crown is an inch and a quarter in 

 length, and nearly an inch across the base; it 

 is conical and trihedral ; the outer and ante- 

 rior surface is convex, the other two surfaces 

 are flattened or subconcave, and converging 

 to an almost trenchant edge directed inwards 

 and backwards ; a ridge separates the convex 

 from the antero-internal flat surface ; both 

 this and the posterior surface show slight 

 traces of a longitudinal rising at their middle 

 part. The lower canine of the male shows 

 the same relative superiority of size as the 

 upper one compared with that in the female 

 in both species of Chimpanzee. The canine 

 almost touches the incisor, but is separated 

 by a diastema one line and a half broad from 

 the first premolar. This tooth (p. 3) is 

 larger externally than the second premolar, 

 and is three times the size of the human first 

 premolar (jp. 3) ; it has a subtrihedral crown, 

 with the anterior and outer angle produced 

 forwards, slightly indicating the peculiar fea- 

 ture of the same tooth in the Baboons, but in 

 a less degree than in the Orang. The summit 

 of the crown of/?, 3 terminates in two sharp 

 trihedral cusps, the outer one rising highest, 

 and the second cusp being feebly indicated 

 on the ridge extending from the inner side 

 of the first ; the crown has, also, a thick ridge 

 at the inner and posterior part of its base. 

 The second premolar (p. 4) has a subquad- 

 rate crown, with the two cu^ps developed 

 from its anterior half, and a third smaller one 

 from the inner angle of the posterior ridge. 

 Each lower premolar is implanted by two 

 antero-posteriorly compressed divergent fangs, 

 one in front of the other, the anterior fang 

 being the largest. The three true molars are 

 equal in s'ze in the Troglodytes Gorilla ; in the 

 Troglodytes niger (Jig. 588.) the first (m. 1) is a 

 little larger than the last (m. 3), which is the 



Fig. 588. 



Dental series, lower jaw, adult male, Troglodytes niger. (Natural Size.^) 



