sixty-five degrees. But this angle depends largely on the protrusion
of the jaws, and varies greatly in species of animals showing much
the same grade of intelligence. In some not especially intelligent
South American monkeys the facial angle amounts to about sixty-five
degrees. In this respect the skull of a chimpanzee reminds us of a
human skull of small cranial capacity and large jaws, in which the
cranium has been pressed back and the jaws crowded forward and
slightly upward.

The weight of the brain in proportion to that of the body has been
considered as of great importance, and within certain limits this is
undoubtedly correct. Thus, according to Leuret, the weight of the
brain is to that of the whole body: In fish, 1:5,668; in reptiles,
1:1,320; in birds, 1:212; in mammals, 1:186. These figures give the
averages of large numbers of observations and have a certain
amount of value. But within the same class the ratio varies
extraordinarily. Thus the weight of the brain is to that of the
whole body: In the elephant, 1:500; in the largest dogs, 1:305; in
the cat, 1:156; in the rat, 1:76; in the chimpanzee, 1:50; in man,
1:36; in the field-mouse, 1:31; in the goldfinch, 1:24.

From this series it is evident that the relative weight of the brain
is no index of the intelligence of the animal. Indeed if the brain
were purely an organ of mind, there is no reason that it should be
any larger in an elephant than in a mouse, provided they had the
same mental capacity. As animals grow larger the weight of the
brain, relatively to that of the body, decreases, and considering
the size of man it is remarkable that it should form so large a
fraction of his weight. Still the fraction in the chimpanzee is not
so much smaller. It is still possible that this fraction is above
the normal for the chimpanzee, for some of the observations may have
been taken on animals which had died of consumption or some other
wasting disease. I have not been able to find whether this
possibility of error has been scrupulously avoided.

A fair idea of the size of the brain may be obtained by measuring
the cranial capacity. This varies in man from almost one-hundred
cubic inches to less than seventy. In the gorilla its average is
perhaps thirty, in the orang and chimpanzee rather less, about
twenty-eight. This is certainly a vast difference, especially when
we remember that the gorilla far exceeds man in weight.

Le Bon tells us that of a series