If the total development of the cerebral cranium from the fourth to the eighteenth year shows a proportion of 12 per cent., the facial development shows an increase of 24 per cent. and that of the nose 39 per cent. Consequently the face increases twice as much as the cranium, and the nose three times as much. In the growth of the face, however, the transverse dimensions must be distinguished from the longitudinal dimensions, because the facial index varies greatly according to the age. The width of the face follows very nearly the same rhythm as the cranium, never exceeding the latter's proportional increase; the length of the face, on the contrary, follows the special rhythm of the growth of the face, which lengthens far more than it broadens.
If we consider the distances of the various points in the profile from the auricular foramen, we find that these distances show a greater increase in proportion as the points in question are further from the forehead and nearer to the chin.
The central section (the nose) and the mandible are the portions which contribute most largely to the increase in length of the face.
While in the case of the cranium there is a very slight, and often imperceptible puberal acceleration of growth, the puberal transformations of the head are, on the contrary, most notable in respect to the face.
The entire region of the upper and lower jaws, but more especially the lower, undergoes a maximum increase during the period of puberty.
In regard to the nose, its rapid growth begins at the time immediately preceding puberty; that is, it undergoes a prepuberal maximum increase. When a boy is about to complete his sexual development, the nose begins to gain in size.
The puberal growth of the mandible has long been a familiar fact, and bears a relation to the development of the sexual glands.
A special characteristic noted by Binet and by myself is that the height of the lower jaw in boys who have reached the prepuberal stage is greater in the boys who are least intelligent; just as in the case of these boys the nose is less leptorrhine and the face less broad. This means that at the period of puberty the most intelligent boys not only have a greater development of head, but also certain distinctive facial characteristics. They should have, for instance, a more ample forehead, a broader face, especially in the bizygomatic diameter (between the cheek-bones), and a leptorrhine nose (infantile leptorrhine type). The backward boys, on the contrary, have a longer face, accompanied by a higher mandible and a flat or "snub" nose. Here are the comparative figures:
Fig. 113.—A child at six months.