Methacrylate-embedded E15 embryo (anterior coronal)
Figure 39 is an anterior coronal slice of the E15 forebrain showing only the differentiating cells outside the presumptive olfactory NEP (which is not in the slice). The densely packed dorsal cells may be the AOB output neurons, and the spindle-shaped cells in the ventrolateral part of the olfactory primordium are probably the oldest mitral cells that have just reached the part that will develop into the MOB. The olfactory nerve fascicles are small bundles that arch over the dorsal part of the olfactory epithelium, beneath the coalesced fascicles in the olfactory nerve that contacts the ventral and medial parts of the bulb. The vomeronasal nerve fascicles exit Jacobson’s organ and always approach the brain on the medial side. The contact zone between the nerve and the brain is a comingling of large cells in the nerve itself and migrating cells in the brain. It is hard to tell which belongs to which so cells may be exchanged between the brain and the nerve.