The materials used in this study were plaster casts of the permanent and deciduous dentitions in Aborigines and several other populations (Table 1).

The samples of Aborigines were selected from the dental casts obtained at the Yuendumu Settlement in Central Australia. These casts were made by the survey of Department of Dental Science, the University of Adelaide, and are now stored in the same Department.

The Japanese samples were obtained from children of kindergartens and high school pupils living in the Tokyo and Hokkaido areas. The Ainu samples were from inhabitants of Hidaka District, the southern part of Hokkaido, whose rate of admixture with the ordinary Japanese had been estimated to be less than 1/2. The materials of American Caucasians were obtained from those living in Chicago, and the American Negro materials were from those living in Washington, D.C., whose rate of admixture with Caucasians was unknown. The Pima Indian materials were selected from the extensive collection of Department of Anthropology, the University of Chicago. All of these materials were directly measured and observed by the present author.

In addition, the data provided by previous authors were also used in computation of some statistical analyses. However, in regard to non-metric characters of the dental crowns, only the data which had been obtained by direct observation of the present author were employed, because there might have been some discrepancies between investigators.

The present study covers all the dentition, both deciduous and permanent, with the exception of the permanent third molars. Most of the materials used in the present study consisted of plaster casts obtained from relatively young individuals for the purpose of making measurements and observations as precisely as possible. In this regard, the numbers of the third molars were so limited that reliable statistical treatment was hardly possible.