These conclusions of Binet are indirectly confirmed by the researches of Vitale Vitali regarding the development of the forehead in school-children; since it is well known that the forehead represents the index of the general growth of the cerebral cranium.
Vitale Vitali based his observations upon school-children and students between the ages of ten and twenty. He not only measured the width of the forehead (_frontal diameter_; see _Technique_), but also measured its height, obtaining the percentage of its relation to the width (frontal index).
FRONTAL INDEX AND DIAMETER ACCORDING TO AGE
(VITALE VITALI: RESEARCHES AMONG SCHOLARS AND STUDENTS FROM 10 TO 20 YEARS OLD)
------------------------------------------ Age | Frontal | Frontal | Amount of | index | diameter | increase ---------+----------+----------+---------- 11 years | 73.05 | 107.5 | -- 12 years | 74.11 | 112.0 | 4.5 13 years | 74.14 | 112.5 | 0.5 14 years | 74.80 | 114.4 | 1.9 15 years | 75.67 | 116.8 | 2.4 16 years | 77.24 | 120.1 | 3.3 17 years | 77.02 | 120.6 | 0.5 18 years | 77.36 | 121.5 | 0.9 19 years | 77.60 | 122.8 | 1.3 20 years | 77.15 | 122.1 | 0.7 ------------------------------------------
Accordingly, between the years of fourteen and sixteen there is a puberal acceleration of growth, accompanied by an elevation of the forehead (high frontal index).
Vitali gives, as extreme limits of the frontal index, 68 and 83.
But in order to give a better illustration of the author's figures, his own words may be quoted: "It appears from our observations that the forehead begins to develop in notable proportions during the fourteenth year, and that the development of the frontal region as compared with the parietal region continues to augment up to the sixteenth year; after this it still increases, but only by a few millimetres, until the end of the sixteenth year. The cephalic development is completed between the sixteenth and eighteenth years. This observed fact is of great importance in relation to the development of the intellect."
The most complete figures at the present time on the growth of the brain, are those of Quétélet, which follow its development from birth until the fortieth year. They are summarised in the following table: