432 THE ANTIQUITY OF MAN 
appeared and the organ has been unified, in all save the 
gorilla, in which the tripartite state is present. As regards 
the characters of the liver the gorilla may be described as 
archaic. The last example I am to cite has a more direct 
bearing on the problem of the Piltdown mandible. In 
the Neanderthal race we find the eyebrow ridges shaped 
as in anthropoid apes ; we suppose that in this ancient 
human race the primitive or anthropoid type of eyebrow 
ridge has been retained. These examples are sufficient 
to show that as new forms of men and apes were evolved 
the incidence of change or of progress on the evolving 
body was local or patchy, some systems of the body being 
affected, others being left untouched. It is therefore 
quite possible that we may encounter such forms as that 
found at Piltdown, in which the characters of one part 
seem to be at variance with those of another — as the 
mandible with the skull. 
We propose, in the first place, to make a cursory 
examination of the simian characters of the Piltdown jaw, 
and to see what significance we must attach to them. 
Before we set out on such a survey, we must obtain a 
clear mental picture of the essential characters of a human 
mandible. In fig. i6o a diagram is reproduced to show 
the chief features which mark the inner or mouth aspect of 
the human mandible. Passing obliquely downwards and 
forwards on this aspect of the jaw, from just behind the 
last molar or wisdom tooth above to below the symphysis 
or union of the two halves of the jaw in front, is a 
narrow linear ridge of bone marking the line along which 
the right mylo-hyoid muscle was attached. The left 
muscle has a similar origin from the opposite half of the 
mandible. From such origins the two mylo-hyoid 
muscles unite along the middle line of the floor of the 
mouth, forming a muscular floor or diaphragm. The 
tongue rests on this muscular floor. In all acts, such as 
swallowing and speaking, the mylo-hyoids come into 
active use in raising the floor and the tongue. The more 
these muscles are used, the stronger they become and the 
more do the mylo-hyoid ridges become emphasised and 
