HUMAN DENTITION. 453 



is no sexual superiority of size, either of the canine or any other 

 single tooth in the human subject. 



Both upper and lower premolars (ib. p.) are bicuspid ; they are 

 smaller in proportion to the true molars than in the Chimpanzee 

 and Orang : in the upper premolars a deep straight fissure at the 

 middle of the crown divides the outer and larger from the inner and 

 smaller cusp : in the lower premolars the boundary groove describes 

 a curve concave towards the outer cusp, and is sometimes oblite- 

 rated in the middle by the extension of a ridge from the outer 

 to the inner cusp, which cusp is smaller in proportion than in the 

 upper premolars. These teeth in both jaws are apparently im- 

 planted each by a single, long, sub-compressed, conical fang : but 

 that of the upper premolars is shown by the bifurcated pulp- 

 cavity to be essentially two fangs, connate, and which, in some 

 instances, are separate at their extremities. 



The crowns of the true molars (ib, m.) are larger in propor- 

 tion to the jaws, are a little larger in proportion to the bicus- 

 pids, and still more so in proportion to the canine and incisor 

 teeth, than in the Chimpanzee and Orang : the contour of the 

 grinding surface is more rounded, and we have seen that the 

 higher Quadrumana already approximate to this character by the 

 angles of the crown being less marked than in the lower Quadru- 

 mana. The first and second true molars of the upper jaw sup- 

 port four trihedral cusps ; the internal and anterior one is the 

 largest and is connected with the external and posterior cusp by 

 a low ridge extending obliquely across the grinding surface, with 

 a deep depression on each side of it, the anterior groove extend- 

 ing to the middle of the outer surface, the posterior one to the 

 inner surface. The enamel is first worn away by mastication from 

 the anterior and internal or largest tubercle : a line of enamel 

 extending from the outside to the middle of the crown is the last 

 to be removed before the grinding surface is reduced to a field of 

 dentine with a simple ring of enamel. (1) It is worthy of remark that 

 by the time when the permanent teeth have come into place the 

 first true molar in both jaws is much more worn, as compared 

 with the second and third molars, than it is in the Chimpanzee 



(1) PI ri'j, fig. 3, VI. 1. 



