| Abstract: | Two human embryos which were immediately before and soon after the appearance of the cerebral vesicle were cut into complete serial sections in almost the same direction and studied comparatively. The findings on these two sets of serial sections indicate that the rostral continuations of subthalamus and ventral thalamus along the ventral thalamic sulcus continuing from the sulcus limitans of the midbrain are destined to give rise to the formation of the cerebral vesicle. The rostral continuation of the subthalamus becomes the floor of the interventricular foramen, and that of the ventral thalamus the pallium. The rostral end of the continuation of the subthalamic matrix is not only the site of the beginning of evagination of the cerebral vesicle, but also the site of elevation of the ganglionic hill or striatum. As the evagination of the cerebral vesicle proceeds exceedingly dorsocaudolaterally from the rostral end of the continuation of the ventral thalamus, the elevation of the striatum occurs also in the same direction, getting in touch with the folding of the hemispheric stalk of Kuhlenbeck to enclose the interventricular foramen. Tt is noticed that, at the beginning of evagination, the grade of depression of the nasal pit was always parallel with that of evagniation of the cerebral vesicle. |
