Developmental changes of the cranial bone thickness in the human fetal period.

The description of the developmental changes of cranial bone thickness in the fetal period is the primary aim of this paper. The materials utilized in this study consisted of the two series. One is those of dry bones of 62 Japanese fetuses ranging from the fifth month to term and the other is those of 56 Japanese fetuses ranging from the fourth month to term. The first series is mainly used for the tests of bilateral difference in the thickness of cranial bones. No statistical significance could be found. Allometry technique was then applied for the analysis in the growth of the thickness of cranial bones and an extremely positive alometric coefficient was obtained. This required us to study another material, i.e., the second series. The materials of the second series were first measured for crown-rump length, head length, head breadth and head circumference. The heads were then carefully dissected and the left side of individual bones of the cranium were removed to take further measurements for the arc length. The thicknesses at the ossification centers and midpoints were successively measured by a micrometer readable to 0.01 mm. The results of the second series were investigated from the viewpoint of absolute and relative growth. By allometric analysis, vertical and transverse arc lengths were found to be isometric with two exceptions, while every measurement of thickness shows an extremely positive allometry. This coincides with the results of the first series.