Methacrylate-embedded E18 embryo (posterior coronal)
Figure 88. This is a slice from the same specimen in Figure 87 cut farther back into the olfactory peduncle where the accessory olfactory bulb occupies the dorsal surface. A dashed-line outline surrounds the settling AOB output neurons—much smaller than mitral cells. The pars externa of the anterior olfactory nucleus may be on either side of the AOB. Layering in the ventrally-placed MOB is like that in Figure 87. Note the many spindle-shaped cells in the internal plexiform layer. The columnar arrangement of the olfactory NEP is in sharp contrast to the various orientations of cells in the olfactory SVZ. Indeed, the SVZ has many spindle-shaped cells that may be a separate population from the migrating cells in the internal plexiform layer. Olfactory nerve fibers coalesce in the ventral and medial part of the olfactory peduncle; some fibers are surrounded by dense cells beneath the bulb that are forming the cribriform plate of the ethmoid bone. Individual olfactory nerve bundles are plentiful at the periphery of the olfactory epithelium. The two sets of mitotic cells are easily distinguished in this slice as well as the one in Figure 87. Jacobson’s organ is beneath the nasal septum, surrounded by a vomer—a bony structure in the ventromedial nasal cavity. Fascicles of the vomeronasal nerve are in the superficial sensory epithelium and on either side of the nasal septum.