TEETH. 



919 



minor particulars in which it differs from the 

 dentition of the Orang, approaches nearer the 

 human type. In the upper jaw the middle 

 incisors (fig. 586, i. 1) are smaller, the lateral 

 ones (ib. i. 2) larger than those of the Orang* ; 

 they are thus more nearly equal to each other; 

 nevertheless the proportional superiority of 

 the middle pair is much greater than in Man, 

 anil the proportional size of the four incisors 

 both to the entire skull and to the other teeth 

 is greater. Each incisor has a prominent 

 posterior basal ridge, and the outer angle of 

 the lateral incisors, *. 2, is rounded off as in 

 the Orang. The incisors incline forwards 

 from the vertical line as much as in the 

 great Orang. Thus the characteristics of the 

 human incisors are, in addition to their true 

 incisive wedge-like form, their near equality 



teeth " *, when the mouth is closed, is appli- 

 cable only to the female, and does not distin- 

 guish the Chimpanzees from the Orangs. In 

 the male of the smaller Chimpanzee (Troglody- 

 tes n/ger) the upper canine is conical, pointed, 

 but more compressed than in the Orang, and 

 with a sharper posterior edge ; convex ante- 

 riorly, becoming flatter at the posterior half of 

 the outer surface, and concave on the corre- 

 sponding part of the inner surface, which is 

 traversed by a shallow longitudinal impres- 

 sion ; a feeble longitudinal rising and a second 

 linear impression divide this from the convex 

 anterior surface, which also bears a longitu- 

 dinal groove at the base of the crown. The 

 canine is rather more than twice the size of 

 that in the female. In the male Gorilla 

 (figs. 585, 586.), the crown of the canine is 



Fis. 5S7. 





Dentition of adult female, Troglodytes Gorilla. (Natural size.} 



of size, their vertical or nearly vertical posi- 

 tion, and small relative size to the other teeth 

 and to the entire skull. The diastema be- 

 tween tlie incisors and the canine on each 

 side is as well marked in the male Chim- 

 panzee as in the male Orang.f The crown 

 of the canine (ib. c.), passing outside the in- 

 terspace between the lower canine and pre- 

 niolar, extends in the male Troglodytes Gorilla 

 a little below the alveolar border of the under 

 jaw when the mouth is shut ; the upper ca- 

 nine of the male Troglodytes niger likewise 

 projects a little below that border ; the 

 seventh character, therefore, which I had 

 formerly assigned to the genus, " apices of 

 canines lodged in intervals of the opposite 



* Compare fig. 586. with pi. xxxii. (Pithecus 

 Wurmb'n) and pi. xxxiv. (Pith. Morio), in vol. ii. 

 Zool. Trans. 



t Compare fig. 586. with pi. xxxii. (PKli. Wurm- 

 lii) in vol. ii. Zool. Trans. 



more inclined outwards : the anterior groove 

 on the inner surface of the crown is deeper ; 

 the posterior groove is continued lower down 

 upon the fang, and the ridge between the 

 two grooves is more prominent than in the 

 Troglodytes niger. Both prcmolars (fig. 586. 

 p. 3 and p. 4) are bicuspid ; the outer cusp of 

 the first and the inner cusp of the second being 

 the largest, and the first premolar consequently 

 appearing the largest on an external view (fig. 

 585.)- The difference is well marked in the 

 female (fig. 587, p. 3, p. 4). The anterior ex- 

 ternal angle of the first premolar is not pro- 

 duced as in the Orang, which in this respect 

 makes a marked approach to the lower Qua- 

 dnnnana. In Man, where the outer curve of 

 the premolar part of the dental series is greater 

 than the inner one, the outer cusps of both 

 premolars are the largest ; the alternating su- 

 periority of size in the Chimpanzee accords. 

 * Zool. Trans, vol. i. p. 372. 

 SN I 



