[Use, in craniology, of vectors for the demonstration of the degree of forehead and face inclination in the chimpanzee and present-day and fossilized man].

It is demonstrated, by mathematical method using vectors, that: (1) the inclination of the forehead, the sign of which is negative (simian type) in all Apes studied here, changes its sign and becomes positive (human type) in Plesianthropus, La Ferrassie I and contemporary Man. It remains negative (simian type) in Sinanthrope XI and La-Chapelle-aux-Saints; (2) the inclination of the face has a positive sign (simian type) in all Apes and Plesianthropus, but becomes negative (human type) in the genus Homo; (3) the fronto-gnathic angle which always remains less than 90 degrees in all Simians, becomes greater than 90 degrees in the genus Homo, and Plesianthropus.