After mitosis, the apical process continues to grow and adheres to the external limiting membran located at the pial surface. The planes of division during later phases are more frequently parallel to the ventricular surface. Due to this, more and more daughter cells leave the cell cycle. They are no longer in contact with the ventricular surface and transfer their nucleus in the direction of the mesenchymal surface.
Mitoses take place in the ventricular zone. Initially, this zone extends over the entire wall of the neural tube. Due to the increasing thickness of the wall, an external layer with few cells (marginal zone) can be seen. This is mainly made up of the elongations of cells located in the ventricular zone. Cells no longer taking part in the cell cycle transfer their nucleus to the area between the ventricular and the marginal zones to form a new layer: the intermediate zone (mantle zone). The majority of these cells are young neurons (proneurons). During the late phase of neurogenesis, an additional zone with mitotically active cells forms between the ventricular and intermediate zones. This is known as the subventricular zone. The formation of these zones represents the general pattern of differentiation of the neural tube.