The author would like to acknowledge the continuing support and encouragement of Professor Kazuro Hanihara, Department of Anthropology, Faculty of Science, The University of Tokyo. She is also indebted to the late Professor emeritus Seiho Nishi, Department of Anatomy, Faculty of Medicine, The University of Tokyo, and to the investigators who collected the data for the Nishi series, without whose work the present study would have been impossible. The author is also grateful to Professor Akio Yamauchi and Dr. Hiroshi Hoshi, Department of Anatomy, Faculty of Medicine, The University of Tokyo, for kindly permitting the use of the Nishi series. Special thanks are due to Mr. Thomas Donahue, Department of Comparative Literature and Culture, Faculty of Humanities, The University of Tokyo, for his kind advice on the preparation of the manuscripts.

Part of this study was financially supported by a grant-in-aid for scientific research of the Ministry of Education, Science and Culture, Japan.