Abstract
The superior surfaces of the temporal lobes of both cerebral hemisphers of Japanese fetuses (23) and new-borns (5) were macroscopically observed and measured to clarify the development and lateralization of the auditory sense area during the course of embryonic growth. 1) The superior surfaces of the temporal lobes of the cerebral hemispheres were firstly visible in the cerebra of 6-month-old fetuses and then the surfaces were marked by occasional undulations in the 7 th month fetuses. Thus, differences appeared between Heschl's convolution (H1) and the planum temporale (Pt) in the 8th month. The morphological pattern of these areas had been divided into seven types in the adult cerebrum, but only the V type had been visible in fetuses, in addition to an alternative type, VI, in the new-bron. Generally, the left hemisphere was broader than the right; this was true in the European fetus as well. The courses of the terminal portion of the posterior branch in the lateral sulcus were horizontal in all left hemispheres and mostly ascending in the right ones. 2) The development of the auditory sense area appeared to be remarkable in the left hemisphere, as compared with the right, in accordance with the measurements of the joint angles of upper and lower margins and inclination angles, as well as with the lengths of lower margins on lateral fossa. 3) The lengths of perpendicular lines for several measurement points surrounded lateral fossa against the Forel line showed that the opercular area belonging to the frontal and parietal lobes tended to be more spread-out in the left side than in the right in examination of the month-by-month development of fetuses and new-borns.
