THE CEPHALIC INDEX
By FRANZ BOAS
I
The top views of the skulls of the races of man show great differences in form. For this reason the shape of the skull has come to be one of the best-studied racial characters. The more or less elongated form of the skull has been proved to be a good means of characterizing varieties of man. The degree of elongation is concisely expressed by the proportion between the antero-posterior diameter or length and the transversal diameter or breadth of the skull. Generally the latter diameter is expressed in percents of the former, and this value is called the cephalic index. The object of the following investigation is a study of the biological significance of this index.
The statement that in a certain race the breadth of the skull is, on the average, a certain percentage of its length, would seem to imply that there exists a certain characteristic relation between length and breadth, so that individuals of a certain length of head would, on the average, have a breadth of head corresponding to the length multiplied by the cephalic index. It is well known that this is not the case, but that the heads which have absolutely the greatest lengths have the lowest indices. I have obtained the following results from a study of 239 Sioux Indians which were measured for me by Mr G. H. Kaven in 1892:
| Number of Individuals. | Length of Head. | Correlated Cephalic Index. |
| 11 | 180-184 mm. | 84.9 |
| 35 | 185-189 | 81.5 |
| 86 | 190-194 | 79.9 |
| 70 | 195-199 | 78.3 |
| 25 | 200-204 | 77.6 |
| 12 | 205-210 | 75.9 |
