Methacrylate-embedded E14 embryo (medial sagittal)
Figure 17 is a medial sagittal slice through the part of the olfactory epithelium that will become Jacobson’s organ. Discrete fiber bundles extend upward toward the basal forebrain, the presumptive vomeronasal nerve that will terminate in the glomerular layer of the accessory olfactory bulb. A separate fiber bundle just below the anterior forebrain surface may be the olfactory nerve. The presumptive olfactory NEP may be in the angle where the neocortical NEP transitions into the basal telencephalic and septal NEP. The basal ganglionic NEP surrounds the eminence created by the expanding subventricular zone and migrating postmitotic neurons. A thin zone of cells that have just migrated out lines most parts of the forebrain NEP. In the region of the future neocortex, these are the Cajal-Retzius neurons in the primordial plexiform layer. More neurons are accumulating outside the presumptive olfactory NEP—probably the AOB output neurons. Postmitotic medial septal neurons may be accumulating outside the septal NEP. The large zone outside the basal ganglionic NEP contains a variety of neurons: the magnocellular basal telencephalic neurons, possibly some layer III neurons in the olfactory tubercle and medial primary olfactory cortex, possibly a few pioneer mitral cells, all were generated on E12 and E13 and some appear to be migrating within the plane of the sagittal section to their settling sites.