It is not easy to suggest how the reduction in size of the canines and front teeth and of the length of the jaw could be of such advantage to incipient man as to lead to the survival of those individuals in which these parts were least developed, and so gradually to the crowding of the teeth, reduced in size, into a jaw of reduced length, whilst at a late stage, long after man was man and no ape, the teeth became so reduced in volume as to leave the lower margin of the lower jaw--projecting far in front of them as the "chin," the eminently human chin. The nutrition of these parts placed in the head near the brain, the great canine having so vast a fang that it reaches up to the eye-socket, whence it is called the "eye-tooth," renders it probable that there is a relation depending on nutrition and blood supply between them and that all-important organ contained in the neighbouring bony box, the brain. As the great teeth and long jaw have dwindled, the brain has increased in volume, and, what is more important, in activity. Other neighbouring bony structures have dwindled whilst the brain has increased. The great longitudinal and transverse crests of bone seen on the skull of the gorilla may never have existed in that form of ape from which man is derived, but a tendency to such ridge-like outgrowth and to a greater thickness of the bony wall of the brain-case characterizes apes as distinguished from men, and its disappearance is one of the changes which have accompanied the expansion of the brain-case and the increased size of brain in man. Lower races of existing men have frequently thicker skulls than the higher races. The bony development of the skull in the higher apes is especially remarkable in the region just above the eye. The upper border of the orbit is greatly thickened, and projects as a bony arch overhanging the eye. But the extent of this growth, as also of crests on the skull, varies in individuals, and is much smaller in females than in males. In the young these ridges and prominences are absent. It is accordingly no very great change that they should disappear altogether in man, even were they as large in the ape-like ancestor of man, which probably they were not. But the existence of a considerable thickening and forward growth of the eyebrow region of the skull is noticed in many human skulls. It is particularly large in some skulls of Australian "black-fellows," and is still larger in and characteristic of the ancient species of men of the Moustierian period in Europe, Homo Neanderthalensis. CHAPTER XXVIII THE BRAIN OF APES AND OF MAN