E13 methacrylate-embedded embryo (lateral sagittal slice)
Figure 9 is a lateral sagittal slice through a deeper part of the invagination of the olfactory placode. Many of the features in this slice are like the slice in Figure 8. The presumptive olfactory nerve is smaller, but some densely-staining cytoplasm extends from the olfactory epithelium into the nerve; these might be the olfactory nerve pioneer fibers.
The dashed line shows the best guess where the NEP ends and the zone of accumulating postmitotic neurons begins. This zone is thicker than in the medial section, mainly due to the tangential cut of the layer. However, over 60% of the AOB output neurons are generated on E13, and the cells accumulating superficially may be sequestered postmitotic neurons in the neuroepithelium preparing for migration.
There is a thick zone of accumulating cells (postmitotic neurons) outside the presumptive basal telencephalic NEP. Most of these cells are destined to settle in posterior parts of the magnocellular basal telencephalic nuclei, where substantial neurogenesis occurs before E13.