[CAMERON] THE HUMAN SKULL 173 



recorded a Melanesian skull' in which the third molars of both the 

 upper and lower jaws had utterly failed to develop. Moreover the 

 dental index is instructive in this relationship for it demonstrates 

 to us that even in the case of the molar-premolar series the space 

 occupied by these teeth is likewise decidedly less in the higher races 

 of modern mankind when compared with the lowest types — the 

 aboriginal Australian, for example. The second great factor in pro- 

 ducing the shrinkage of the dental arcade has been the reduction in 

 the size of the individual teeth which has been going on progressively 

 and consistently from the anthropoid stage, throughout the fossil 

 hominidae and the lowest types of modern hominidse right up to the 

 white races, where they reach their minimum size. 



Fig. 10 has been devised to render these above points more effec- 

 tive. It shows the Heidelberg jaw,^ the Piltdown jaw and a modern 

 jaw, all reduced to two thirds their normal size. The line AB has 

 been drawn along the alveolar margin in each case. I found on 

 measuring this distance in the Heidelberg and Piltdown specimens that 

 it was exactly the same in both. In the modern jaw, on the other hand, 

 I ascertained that this distance had become shrunken to the extent 

 of the gap AC which is 11 per cent of the distance AB, and this, it may 

 be noted, is a very considerable amount indeed. One might measure 

 the amount of this contraction by the angle AFC (P being the pogonion) 

 which was found to be 30-5 degrees, thus representing a substantial 

 degree of movement backwards of the point C. Another instructive 

 fact gleaned from Fig. 10 was that the distance along the line AB 

 occupied by the teeth was exactly the same in the Heidelberg jaw 

 and the modern jaw, whereas this distance was found to be nearly 

 half as much again in the Piltdown specimen. Of course in measuring 

 this space one would have to make allowance to a considerable extent 

 for the inward curvature of the mesial portion of the alveolar border. 

 Apart from this drawback the figure yields some striking points of 

 comparison. 



Some evolutionists have laid stress on the fact that the evolution 

 of the chin in man has been intimately associated with the conferring 

 of the gift of speech. Certainly some support is given to this state- 

 ment by the well known fact that in some types of microcephalic 

 idiot where the chin is very feebly developed (see Fig. 14), these un- 

 fortunate individuals are frequently incapable of the power of articu- 

 lation. However, the explanations of this defect have not always 

 been very definite or convincing. It has been suggested by other 

 authorities that it may be due to some interference with the proper 



^ op. cit. 



- See the elaborate memoir by Schotensack, published at Leipzig, 1908. 



