TEETH OF DIPHYODONTS. 325 



instances, especially in the Melanian varieties, from the middle of 

 the grinding surface, at right angles to that dividing the two 



O O O O O 



outer cusps, to the posterior border of the tooth. 



The first upper molar is always implanted by three diverging 



fangs, two external and one internal. The second molar is 



~ ' 



usually similarly implanted, but the two outer fangs are less 

 divergent, are sometimes parallel, and occasionally connate ; this 

 variety appears to be more common in the Caucasian than in the 

 Melanian races ; and in the Australian skulls the wisdom tooth 

 usually presents the same three- fanged implantation as in the 

 Chimpanzee and Orang. 



The crowns of the inferior true molars are quinque-cuspid, the 

 fifth cusp being posterior and connected with the second outer 

 cusp : it is occasionally obsolete in the second molar. The four 

 normal cusps are defined by a crucial impression, the posterior 

 branch of which bifurcates to include the fifth cusp ; this bifurca- 

 tion being most marked in the last molar where the fifth cusp is 

 most developed. In the first molar a fold of enamel, extending 

 from the inner surface to the middle of the crown, is the last to 

 disappear from the grinding surface in the course of abrasion. 

 The wisdom-tooth, fig. 257, in 3, is the smallest of the three 

 molars in both jaws, but the difference is less in the Melanian 

 than in the Caucasian races. Each of the three lower molars is 

 inserted by two sub-compressed fangs, grooved along the side, 

 turned towards each other. This double implantation appears to 

 be constant in the Melanians, especially the Australian race, in 

 which the true molars are relatively larger than in other blacks. 

 In Europeans it is not unusual to find the two fangs in both the 

 second and third molars connate along a great part or the whole 

 of their extent. 



With respect to the reciprocal apposition of the teeth of the 

 upper and under jaw, it is interesting to observe that the crown 

 of the lower canine is, as usual, in advance of that above, and fits 

 into the shallow notch between that and the lateral incisor. The 

 inferior incisors are so small that their anterior surface rests 

 against the posterior surface of the upper ones when the mouth 

 is closed ; the other teeth are opposed crown to crown, the upper 

 teeth extending a little more outwardly than the lower ones. 



The deciduous series of teeth in the human subject, fig. 258, 

 consists of 



.2.2 1.1 2.2 

 '^ ;C Li ;m 2T2 =20 ' 



The upper milk incisors of the Chimpanzee are relatively larger 



