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Methacrylate-embedded E15 embryo (medial sagittal)

Figure 33 is a medial slice through Jacobson’s organ and the olfactory epithelium.  The olfactory recess of the lateral ventricle is a prominent ventral dip in front of the presumptive medial basal telencephalic and septal NEP, which gives us a hint of the position of the olfactory NEP in the basal forebrain.  The olfactory nerve melds with the superficial brain in a large contact zone.  Cells are migrating out of the NEP radially, and some appear to be migrating toward the evaginating olfactory bulb.  Lots of cells are accumulating beneath the olfactory NEP, many of these are possibly the AOB output neurons.  The germinal source of these output neurons cannot be identified accurately.  Possibilities are the olfactory NEP itself or the adjacent basal telencephalic NEP.  This slice shows fiber fascicles and associated large supporting cells exiting Jacobson’s organ in several narrow bundles the extend ip toward the brain.  The olfactory nerve bundles start out as small fascicles, but group together in one large olfactory nerve that surrounds the anterior basal forebrain.  An interesting phenomenon is the pyknotic debris that is shedding into the nasal cavity from a specific part of the mucosal epithelium.  We will see that in more than one specimen on E15.