466 
THE ANTIQUITY OF MAN 
"caninism," are shown in fig. 172 — the stages seen 
in man, the female chimpanzee, the male chimpanzee, 
and the male gorilla. There are two definite facts we 
may rely on. (i) That caninism varies in degree 
according to the kind of anthropoid. It reaches its 
greatest development amongst gorillas. (2) That the 
degree of development is influenced by sex. Amongst 
the great anthropoids males have the canine teeth 
more developed than females. Amongst the small 
anthropoids — the gibbons — both sexes have long canines. 
Now there can be no doubt that secondary sexual 
characters — to a certain degree caninism is such a 
30 20 10 40 30 20 10 50 46^0 20 10 O 60 50 
AUSTRALIAN* CHIMPANZEE^ CHIMPANZEE i 
GORILLA"? 
Fig. 172. —The development of the canine teeth in an Australian native, 
a female chimpanzee, a male chimpanzee, and in a male gorilla. 
character — are regulated in development and growth 
by substances formed in the genital glands. We have 
evidence that the growth of canine teeth can be regulated 
by internal secretions or hormones. In that peculiar 
disease or disturbance of growth, acromegaly, which 
sometimes attacks men or women, the jaws and the 
parts of the skull concerned in mastication are particularly 
liable to become overgrown. The growth of the jaws 
is also influenced, during normal development, by 
secretions or substances thrown into the circulating blood 
by such glands as the pituitary and thyroid. A survey 
of the dental and maxillary development of the higher 
primates reveals such various degrees of caninism as are 
