Temporal changes of the Bony-birth canal

—An examination on the relationship of the cranial shape—

Abstract

This study examined the temporal changes of the bony-birth canal from Jomon to modern Japanese in order to test the hypothesis that the bony birth-canal form of the mother is one of the decision factors of the cranial shape. The outcomes are as follows, Jomon population had the biggest bony-birth canal. In Yayoi and the Medieval populations, the sagittal diameter of the pelvic inlet is relatively short, and the transverse diameter of the pelvic inlet is long. In the early modern, the modern and the present populations, the sagittal diameter of the pelvic inlet is relatively long, and the transverse diameter of the pelvic inlet is short. All measurements of the pelvic outlet continue to decrease from the Jomon period onward. This study also examined correlations between the temporal changes of the pelvic inlet and those of the cranial shape. The temporal changes of the pelvic inlet shape were correlated with the temporal changes of the cranial shape. These results support the hypothesis that the bony birth-canal form of the mother is one of the determining factors of the cranial shape. It was also shown that the size of the bony-birth canal was not correlated with the temporal change of stature. This shows that the size of the bony-birth canal is not associated with the body size.