The enclosing of the neural tube begins at the developmental stage of 5-6 somites in human embryo. The neuroporus anterior closes in at the stage of 20 somites after Sternberg, the neuroporus posterior a little later at that of 25 somites, which embryos are about 2.5mm long. In 5mm long one seems to become the neural tube completely free from the ectoderm.
The differentiation of fore-, mid-and hind-brain is distinct already before the enclosing of the tube. The forebrain begins its differentiation as a part of hemispheric vesicles at the cranial end of the closed tube, so that the boundary between telen-and diencephalon becomes distinct at the Streeter's horizon XV. After Kahle the differentiation of the tube wall from the matrix proceeds as beginning, advanced and full migration, and then as beginning, advanced and complete exhaustion. Such differentiation of the tube wall begins at first in the subthalamic region already at the Streeter's horizon XIV.(Fig.1 Pl.1.) before the appearance of the hemispheric vesicle. This beginning migration of the matrix in the subthalamus is advancing in the next horizon XV (6mm), XVI (9mm) and becomes full with discernible corpus subthalamicus in the stage XVII of 12.6mm. long embryo.(Fig.11., Pl.2), while in regions of dorsal thalamus and hypothalamus the migration of matrix is only beginning, which condition remains almost the same in the next horizon XVIII.(18, 20mm), whilst in the subthalamus of these specimens there begins exhaustion of matrix.(Fig.15, 18, Pl.3). This exhaustion of matrix advances further up to 35mm long specimen, in which the striatum is differentiated into caudatus and putamen, pars pallida from the hypothalamus, the dorsal thalamus is in full migration.(Fig.23, 24, Pl.4). This differentiation of striatum begins at the stage of 20mm long embryo.
In the horizon XV. of 6mm long embryo the hemispheric or cerebral vesicle is situated as prolongation of subthalamus and ventral thalamus so that it continues dorsal to the dorsal thalamus, ventral to the hypothalamus. In this specimen the nerve fiber layer is already observable on the outer surface of subthalamus and ventral thalamus, the most dorsal part of which is the Kuhlenbeck's zona limitans intrathalamica, the most ventral part the Gilbert's hypothalamotegmental tract. Between these tracts spreading layer may contain striotegmental, striothalamic fibers.(Fig.2-6, Pl.1)
In the next developmental stage of 9mm long embryo the cerebral vesicle is protruding toward dorsal and behind so that the ventral and to hypothalamus continuing part becomes thick to indicate the orgin of striatal ridge.(Fig.7-10. Pl.2) Moreover in this stage the epithalamic part becomes distinct, beginning the layer of the stria meclullaris thalami, the other nerve fiber layer is the same as in the earlier stage except the commissural and chiasma plates. There is no hippocampal ridge on the medial surface of the hemisphere. The hippocampal ridge appears at first in the next developmental horizon XVII of 12.6mm long embryo, on the outer surface of which becomes the nerve fiber layer thick, which layer continues, although not so very thick, on the dorsal and hind surface of the hemisphere.

View full abstract