THE GLENOID FOSSA IN THE SKULL OF THE ESKIMO. 7 



Here, however, it will be necessary to make a slight digression, 

 as some views of Dr. Keith 1 help to throw much lighten the pres- 

 ent investigation. He remarks that in all anthropoid forms, 

 both recent and extinct, the canine teeth are so developed that 

 a side to side grinding movement in mastication is impossible; 

 that the canine teeth are developed to prevent such a movement, 

 and that they serve as guides to prevent the jaws from "skidding" 

 or slipping when brought forcibly into action; that in crushing 

 their food, the lower teeth ascend more or less forcibly against 

 the upper. 



Dr. Keith then goes on to show that in Mousterian man 

 the form of the palate had far departed from the anthropoid 

 type, and that this departure, made possible by the subsidence 

 of the canine teeth to the level of their neighbours, was due to 

 the evolution of a new form of mastication, namely, a side-to- 

 side chewing movement. Now the palate of Mousterian man 

 was remarkable for its horseshoe shape and its relatively great 

 width, while the dental roots of the Mousterian race were highly 

 specialized. The roots of the teeth from St. Brelade bay, 

 Jersey, were remarkable for their fusion due to the great hyper- 

 trophy of their dentine and cementum and, as Dr. Keith has 

 pointed out, it seems clear that these features were due to the 

 side-to-side grinding movement in mastication, "the fusion of 

 the roots being a result of overgrowth to withstand the great 

 lateral strain thrown on the teeth in a side to side mastication," 

 whilst "the great width of the palate was also due to the pre- 

 ponderance of the side to side movement." .... "In modern 

 races," on the other hand, "especially highly civilized races, 

 a modified form of the anthropoid bite has reasserted itself. 

 In place of the canines serving as guides to prevent a side to 

 side movement the lower incisors bite and pass upwards behind 

 the upper ; the incisor teeth serve to insure a vertical and scissor- 

 like action of the teeth. With the evolution of the modern and 

 overlapping bite and diminution of the side-to-side movement 

 there is a tendency to narrowing of the palate." 



1 See a description of teeth of palaeolithic man from Jersey by A. Keith 

 and F. H. S. Knowles, Journ. Anat. and Phys., Vol. 46. 



