324 ANATOMY OF VERTEBRATES. 



Both upper and lower premolars, fig. 257,ps an d 4, 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 boun- 

 dary groove describes a curve concave towards the outer cusp, 

 and is sometimes obliterated 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 implanted each by a single, long, subcom- 

 pressed, 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 separated at their extremities. 



The crowns of the true molars, fig. 257, m l, 2, 3, are larger in pro- 

 portion to the jaws, are a little larger in proportion to the bicuspids, 

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

 than in the Chimpanzees and Orangs. The contour of the 

 grinding surface is more rounded, and the angles of the crown 

 are less marked in the higher than in the lower Quadrumana. 

 The first and second true molars of the upper jaw support four 

 triedral 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 extending to 

 the middle of the outer surface, the posterior one to the inner sur- 

 face. 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 den- 

 tine with a simple ring of enamel. 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 more worn, as compared with the 

 second and third molars, than it is in the Chimpanzee or Orang, 

 owing to the slow attainment of maturity characteristic of the 

 human species, and the longer interval which elapses between the 

 acquisition of the first and the last true molars, than in the 

 highest Quadrumana. In the last true molar, called from its late 

 appearance the ' dens sapiential,' or wisdom-tooth, the two inner 

 tubercles are blended together, and a fissure extends in many 



and 150 (vol. ii.); but truth compels the remark that the lemur and ape are sepa- 

 rated by numerous gradational species ; whilst between the ape and man there is no 

 known connecting or intermediate link. Logicians have long ago exposed and branded 

 the sophism which has of late been propounded to persuade men that they arc of the 

 order of apes. 



