[CAMERON] THE HUMAN SKULL 175 



i!\ustralian. In designing Fig. 11, it was first of all found that the 

 average modern dental arch required to be slightly enlarged so as to 

 get any of the teeth to coincide. It was then ascertained that the 

 second molars were the only ones that would thus coincide with 

 one another, all the other teeth being placed at gradually increasing 

 distances from one another. The second molars thus appear to repre- 

 sent the fixed points from which the alteration in the curve of the 

 dental arch has proceeded. All the teeth in front of these have been 

 deliberately forced backwards and inwards, the amount of this move- 

 ment becoming gradually greater as one proceeds in a forward direction, 

 until it reaches its maximum in the case of the central incisors. The 

 third molars even must have been very slightly forced inwards in this 

 evolution process, as the figure indicates, though this does not occur 

 in every case. The general efïect of this movement of course has been 

 to crowd the front teeth very closely together, but even then they 

 could not have been accommodated in the restricted space left at 

 their disposal unless there. had been some concomitant reduction in 

 their size. Now this has been definitely proved in the case of the 

 canine tooth of the Piltdown jaw by Woodward and Dawson^ who were 

 fortunate enough after immense labour to discover a specimen of this 

 a short time after the skull was unearthed. These observers have 

 shown definitely that the canine tooth of the Piltdown jaw was de- 

 cidedly larger than that of modern man, and was indeed quite ape-like, 

 as mentioned above. Probably the incisors and premolars of the 

 Piltdown jaw would have had to become reduced in size in a propor- 

 tional manner, as Fig. 11 suggests. This fact must, however, be left 

 for the future to prove, since a complete dental arch for the Piltdown 

 type has yet to be discovered. 



The preceding paragraph has dealt entirely with the effects of 

 the teeth upon the evolution of the lower jaw. It is of course obvious 

 that the dental arches of both the upper and lower jaws must undergo 

 the same evolutionary process simultaneously, so that the "bite" 

 of the individual may always remain the same at all stages. The 

 same statement must apply with equal force, and in the same measure 

 to the evolution of the jaws themselves. 



The sphenomaxillary angle has proved a most useful angular 

 measurement to illustrate the progress that has been made in the 

 evolution of the orthognathous type of skull from the prognathous. 

 This angle it may be mentioned is included between lines joining the 

 Prosphenion to the Basion and the Prosthion." In the orang-utan it 



1 op. cit. This tooth proved to be the upper left canine. 



2 I have adopted Duckworth's {op. cit.) method of measuring this angle as I 

 consider it preferable to that of Huxley. 



