>>10910667The negro skull, in addition to having a smaller brain volume and thicker cranial bones than that of the White, is prognathous ; i.e., the lower face projects forward in the manner of an animal's muzzle. The negro jaw is substantially longer, relative to its width, than the White jaw. A feature of the negro lower jaw is its retention of a vestige of the "simian shelf," a bony region immediately behind the incisors. The simian shelf is a distinguishing characteristic of apes, and it is absent in Whites.