Studies on the Development and Cytoarchitectonics of the Premotor Area (Brodmann's Area 6) of the Cerebral Cortex of the Fetus

Abstract

The authors studied on the development and cytoarchitectonics of the cerebral cortex in the Brodmann's area of (j in the 119 (male 64, female 55) Korean fetal brains and summarized the result as follows; 1. The thickness of the cerebral cortex was very thin of 0.21mm at the f()Urth month of fetal age and increased very rapidly in the fifth and sixth month, slowly from the seventh to the ninth month, and very rapidly again in the tenth month. As to the relation between brain weight and the thickness of the cerebral cortex, the thicknes of the cerebral cortex was very thin under 50gm of brain weight; increased very rapidly until the brain weight gaind to 101-150gm. thereafter increased slowly to 400gm. and increased very rapidly again over 401gm of the brain weight. 2. The differentiation of the lamination of the cerebral cortex began a diverge in the sixth fetal month, and the lamination of the cortex occurred almost completely at the seventh fetal month. As the relation of the defferentiation of the cerebral cortex with the brain weight, it began a diverge from 51gm to 100gm of the brain weight. but there might be an individnal difference of Ianination. 3. The relative cell density of the cerebral cortex cannot be measured under the fifth month of fetal age. The relative cell density of the cerebral cortex was very high in the sixth and the seventh fetal month and thereafter it decreased gradually as the increase of fetal age. As the relation of the relative cell density with the brain weight, the relative cell density was very high up to 150gm of the brain weight and thereafter it decreased gradually as the increase of the brain weight. The absolute cell density was found the resemblance of the relative cell density. 4. The nerve cells of the fetal cortex might be increased very rapidly up to the seventh month of fetal age and thereafter the number of the nerve cells of the cortex might be stabilized. 5. Thickness of the cortex. the relative cell density and absolute cell density of the cerebral cortex had almost no sexual difference