THE PILTDOWN MANDIBLE 451 
In the preceding paragraphs, the evidence relating to 
the masticatory function of the Piltdown mandible has 
been reviewed with the definite object of seeing whether 
we can reconcile its simian characters with a brain and 
skull which are distinctly of a human type. In the mid- 
Pleistocene man of La Chapelle the brain had a volume 
of 1620 c.c, the mandible a masticatory area which, from 
the reconstruction by Professor Boule, I calculate to have 
been 3450 mm.^ A brain volume of 1400 c.c. and a 
mandibular chewing area of 3980 mm.^, as in the writer's 
reconstruction of the Piltdown mandible, seem, when 
we keep the La Chapelle example in mind, quite a 
reasonable combination. We cannot reject this mandible 
because of its anthropoid dimensions and characters. 
Before passing on to the next chapter, in which the 
evidence relating to teeth is to be considered, it will be 
well to draw attention to some very instructive facts 
brought out in the drawings shown in figs. 165, 166, and 
167. So far we have centred our attention on the upper 
maro^in of the mandibular arch — the tooth-bearing margin. 
We must now examine the changes which have taken 
place at the lower margin which bounds the floor of the 
mouth. In the chimpanzee (fig. 165) the lower margin 
invades and diminishes the floor of the mouth, especi- 
ally in the anterior or symphyseal region. The lower 
border of the symphysis lies 25 mm. behind the cutting 
edge of the incisor teeth, which form the anterior border 
of the mouth area. In the gorilla the symphysis may 
extend backwards ^^ mm. into the floor ; in Dr Smith 
Woodward's reconstruction it reaches backwards 37 mm. 
(fig. 166, A) ; in the reconstruction by the writer 30 mm. 
(fig. 166, B) ; in the Heidelberg jaw 29 mm. (fig. 167, A) ; 
while in the modern English mandible (fig. 167, B) the 
distance is only 13 mm. The widening of the aperture 
of the buccal floor has occurred at the sides as well as 
in front at the symphysis. Thus we see that in the 
evolution of the mandible of modern man a double 
change has been at work : while the teeth and the 
upper margin of the mandibular arch have undergone a 
