442 THE ANTIQUITY OF MAN 
condyle ensures a rapid opening of the mouth. It does 
more. When the condyle has mounted the eminence, 
the lower series of teeth is nearly parallel to the upper, 
not divergent as would be the case if the joint movement 
were of the hinge type. When the three great muscles 
press the lower teeth against the upper, crushing the food, 
the condyle slips home to its socket — the glenoid cavity 
in front of the ear. It will be seen that, as the teeth 
meet and the movement comes to an end, there must be 
a certain degree of rubbing between the teeth, for the 
condyle passes backwards as it sinks home and the 
condyles do not come to rest exactly at the same point of 
time, giving the teeth a lateral movement. We expect, 
therefore, that the chewing surfaces of the Piltdown teeth 
should be worn flat, for the highly developed articular 
eminence and deep glenoid cavity proclaim in unmistak- 
able terms that the chewing movements just described as 
true of modern man are also true of him. The chewing 
surface of the Piltdown molars are worn smooth and flat. 
That is a strong point in favour of the authenticity of 
the jaw. 
An articular eminence of the kind just described has 
until now only been seen in human races built on the 
modern type. We naturally regard the form of joint 
found in anthropoids as the more primitive — the form 
from which we believe the human one has been evolved. 
The temporo-maxillary joint of a chimpanzee is shown in 
fig. 164, the mandible being represented in both the 
opened and closed positions. A passing glance may lead 
the reader to the conclusion that an articular eminence 
is absent, but a closer examination will reveal the fact 
that it is not the eminence but the glenoid cavity which 
is missing. If figs. 163 and 164 be compared, it will be 
seen that in the first the floor of the glenoid cavity reaches 
upwards to the level of the roof of the ear-passage, while 
the projection of the articular eminence is nearly on the 
level of the floor of the ear-passage. In the latter (fig. 
164) the articular plateau on which the condyle moves is 
level with the floor of the ear-passage. In the chimpan- 
