shifting of the cerebrum over the cerebellum. As the gradual filling up of the cranial cavity progressed necessarily pari passu with these modifications, we have, in the facial angle of Camper, a rough mechanical means of estimating the advance of mental development during the period of man's existence as a human being, i.e. since he attained the erect attitude.
Among the minor results of this retrocession of the facial bones was a gradual contraction of the alveolar borders of the jaws, thus crowding the teeth into a smaller space. The consequence was that the third molar teeth, which were the largest, or at least the same size as their neighbours, in the jaws of the Palæolithic races, became gradually smaller, until in civilized races they have dwindled into almost vestigial organs.
Another distinction between the earlier fossil skeletons and those of modern civilized races is that the latter have well-formed chins, forming a striking contrast to the simian-like mandibles of the former, as shown in Fig. 1. This is the most remarkable feature of the recently discovered Piltdown mandible in Sussex (see Fig. 9). Whatever may be the precise cause of this peculiarity, there can be no doubt that the gradual formation of the human chin has a remarkable parallelism with the progress of man's intellectuality, ever since he diverged from the common stem line from which he and the anthropoid apes have descended.
There are thus two distinct lines on which
