THE TEETH OF FOSSIL MAN 463 
the movement. When, however, 1 biting movement is 
carried out, one in which the edges of the lower incisors 
are made to meet the opposing edges of the upper 
incisors, the temporal muscle is felt to remain passive ; 
the muscles which carry out this movement are the two 
which lie in the cheek — the masseter on the outer side of 
the ascending ramus of the mandible, and the internal 
pterygoid on its deep or buried aspect. In the inhabitants 
of our western cities the biting mechanism has fallen 
into disuse. The overlapping incisor bite has appeared. 
The cheeks, which are high and prominent when the 
biting muscles — -the masseter and internal pterygoid — 
are well developed, become reduced and sunken, giving 
us our narrow, hatchet-shaped faces — our oval cast of 
countenance. 
I have cited those modern tooth changes to introduce 
another aspect of the Piltdown problem. It is clear, if 
we are right in differentiating the biting from the 
chewing mechanism, that this observation will influence 
us when we come to interpret the Piltdown mandible. We 
have already seen that the front teeth and the corresponding 
part of the jaw were developed to a superhuman degree ; 
they were almost anthropoid in size and form. We may 
further assume that the biting muscles were large in 
Eoanthropus. We have to determine whether the bite 
of Eoanthropus was similar in all respects to that of 
anthropoids, or represented a transitional stage between 
the primitive human and anthropoid methods of using 
the" front teeth. In fig. 171 the problem has been given 
a concrete representation. On one side is shown the 
manlier in which the lower front teeth come into contact 
with the upper ones in the skull of that primitive extinct 
race — the Tasmanians. On the other the front bite of 
a female chimpanzee is shown. Our present knowledge 
leads us to regard the arrangement in the chimpanzee 
as the more primitive — the one which more nearly re- 
sembles the common type from which both forms have 
been evolved. The upper teeth represent the stationary 
blade of the dental shears, and the lower incisors — two 
