THE BONES 61 



form instead of an equilateral, an isosceles triangle, the sides 

 being greater than the base. Hence the proboscidate character 

 of such skulls. 



The leading peculiarity of the human jaw, distinguishing it 

 from that of the highest anthropoids, and of all other mam- 

 mals, is the projection in the middle of its exterior surface, the 

 protuberance of the chin. Compared with the most ancient 

 human jaws from the Palaeolithic Age (La Naulette, Sipka, 

 Krapina), the lower jaw of the Homo recens, with its more or less 

 strongly defined chin, has undergone marked improvement. 



The most varied opinions prevail as to how the formation 

 of the chin and the consequent improvement in the form of the 

 jaw was brought about. Walkhoff assumes that the trajectories 

 of the Musculus digastricus and especially of the M. genio- 

 glossus have been the chief factors in determining the growth 

 of the chin. Weidenreich holds the view that the development 

 of the chin is due to a reduction in the size of the teeth, and of 

 the alveolar edge of the lower jaw, but this is probably erroneous, 

 since, at the present day, man, civilised and uncivilised, possesses 

 a chin in spite of his teeth being almost as large as those of 

 palaeolithic man. 



Toldt believes the true cause to lie in the development of 

 the form of the head, particularly in the broadening of the 

 frontal part of the skull, which has lead to a corresponding in- 

 crease in the width of the face and of the lower jaw ; in order 

 to relieve the consequently great tension of the lower jaw the 

 bones were strengthened at the point of union of the two halves. 

 This first takes place at the time of birth, appearing as the 

 ossicula mentalia in the median symphysis and forming the 

 starting-point for the structure of the chin. It did not originally 

 exist in the earliest races of man, but has developed gradually 

 in the course of time under the influence of the function it was 

 to perform. Hence, according to Toldt, 1 the chin is correlated 

 to the whole structure of the head and is a material advantage 

 possessed by man over all the other animals ; it is, by no means, 

 to be regarded as a sign of weakness or degeneration, which it 

 would be were it traceable to a reduction of the teeth. 



Another important difference between man and the other 



J C. Toldt, Vienna, Corr.-Blatt f. Anthropol., etc., 1904, pp. 94-98. 



