770 



come into place in the upper jaw. The mature dentition, though in all its principal charac- 

 ters strictly Quadrumanous, yet, in the minor particulars in which it differs from the den- 

 tition of the Orang, approaches nearer the Human type. In the upper jaw the middle incisors 

 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, and the proportional size of the four incisors both to the entire skull and to the other 

 teeth is considerably greater. 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 the canine on each side is as well-marked in the male Chimpanzee as in the male 

 Orang. The crown of the canine, passing outside the interspace between the lower canine 

 and premolar, extends a little below the alveolar border of the under jaw when the mouth is 

 shut : the character, therefore, which had been deemed generic, ' apices of canines lodged in 

 intervals of the opposite teeth, when the mouth is closed,' is applicable only to the female, 

 and does not distinguish the male Troglodytes from Pithecus. The upper canine of the 

 male Troglodytes niger is conical, pointed, but more compressed than in the Orang, and 

 with a sharper posterior edge ; convex anteriorly, becoming flatter at the posterior half of 

 the outer surface, and concave on the corresponding part of the inner surface, which is 

 traversed by a shallow longitudinal impression : a feeble longitudinal rising and a second linear 

 impression divide this from the convex anterior surface, which also bears a longitudinal groove 

 at the base of the crown. The canine is rather more than twice the size of that in the female. 

 Both premolars 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. The difference is less marked in the female. The anterior external angle of the first 

 premolar is not produced as in the Orang. 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 superiority of size in the Chimpanzee accords with the straight 

 line which the canine and premolars form with the true molars. 



The true molars are quadricuspid, relatively larger in comparison with the bicuspids than 

 in the Orang : the last is the smallest by the feeble development of the two hind cusps. In 

 the first and second molars 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, than in the Chimpanzee. A low 

 ridge girts the base of the antero-internal cusp of each of the upper true molars in the male 

 Chimpanzee : it is less,marked in the female. The premolars as well as molars are severally 

 implanted by one internal and two external fangs, diverging but curving towards each other 

 at their ends as if grasping the substance of the jaw. 



In the lower jaw the lateral incisors are broader than the middle ones, but have their outer 

 angle rounded off ; they are all much larger and less vertically implanted than in Man. The 

 lower canines are two inches in length, including the root ; the enamelled crown is three- 

 fourths of an inch in length, and two-thirds of an inch across the base ; it is conical and tri- 

 hedral ; the outer and anterior surface is convex, the other two surfaces are flattened or sub- 

 concave, and converge to an almost trenchant edge directed inwards and backwards ; a ridge 



