Methacrylate-embedded E14 embryo (posterior coronal)
Figure 24 slices the anterior lateral ventricle in a region where the olfactory nerve is very close to the ventral brain. A single vomeronasal nerve bundle extends upward toward the brain within the plane of the slice. There is a thick layer of cells outside the presumptive olfactory NEP—mostly unidentified neurons generated on E12 and E13. Some AOB output neurons may be migrating from the medial part of this NEP (dashed-line arrows). The bulge of accumulating cells outside the ventromedial forebrain are most likely medial septal neurons that were generated on E13 (solid-line arrow). The neocortical NEP shows an interesting maturation gradient. Blood islands are common in parts of the NEP that have more cells outside it, but are absent dorsal and medial where there is only a thin layer of outside cells. That matches the neurogenetic and maturation gradients in all layers of the cerebral cortex—ventrolateral areas have older neurons and mature earlier than dorsomedial areas.