320 ANATOMY OF VERTEBRATES. 



one, the outer cusps of both premolars are the largest ; the 

 alternating superiority of size in the Gorilla accords with the 

 straight line which the canine and premolars form with the true 

 molars. In fig. 255, m i, m 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 Troglodytes a low 

 ridge connects the antero-internal with the postero-external cusp, 

 crossing 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. In Troglodytes 

 niger the last molar is the smallest, owing to the inferior develop- 

 ment of the two hinder cusps, and the oblique connecting ridge 

 is feebly marked. In 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 i or 

 m s, having the posterior outer cusp, and particularly the pos- 

 terior inner cusp, more distinctly developed than in Troglodytes 

 niger. The repetition of the strong sigmoid curves which the 

 unworn prominences of the first and second true molars present 

 in Man, is a very significant indication of the near affinity of the 

 Gorilla as compared with the approach made by the Orangs or 

 any of the inferior Quadrumana, in which the four cusps of the 

 true molars rise distinct and independently of each other. A 

 low ridge girts the base of the antero-internal cusp of each of the 

 upper true molars in the male Chimpanzees ; it is less marked in 

 the female. The premolars as well as molars are severally im- 

 planted by one internal and two external fangs. In no variety of 

 the human species are the premolars 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 varie- 

 ties, and more particularly that race inhabiting Australia, that I 

 have found the ' wisdom-tooth,' fig. 257, m 3, with three fangs as a 

 general rule ; and the two outer ones are more or less confluent. 

 The lower canine of the male (figs 253, 256, c), shows the same 

 relative superiority of size as the upper one, compared with that 

 in the female, in both species of Troglodytes. 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 ex- 

 ternally than the second premolar, and is three times the size of 

 the human first premolar, fig. 257, p 3 ; it has a subtriedral 

 crown, with the anterior and outer angle produced forward, 

 slightly indicating the peculiar features of the same tooth in the 



