Methacrylate-embedded E21 embryo in the sagittal plane (medial)
Figure 129. This medial sagittal slice cuts through the dense olfactory NEP and SVZ continuous with the basal telencephalic NEP and SVZ (the olfactory recess is lateral to the slice) . The AOB in the posterodorsal part of the bulb does not form a prominent “hump,” because it is also lateral to this slice. The borders of the mitral cell layer in the MOB are distinct as fewer clusters of cells move in from the internal plexiform layer. There are widely-spaced tufted cells among the fibers in the external plexiform layer. Many fibers are crisscrossing in the olfactory nerve/glomerular layers. Spindle-shaped cells appear to be migrating into the internal plexiform layer in the ventral MOB near the anterior anterior olfactory nucleus. Coalesced fiber bundles of the olfactory nerve surround the bulb and form a thick ventral bundle. Individual bundles of the olfactory nerve penetrate the undulations of the cribriform plate of the ethmoid bone; the bone grows around the olfactory nerve bundles. Most of the olfactory epithelium is composed of large olfactory sensory neurons with darkly-staining cytoplasm; some of the dark cells are collapsed—an artifact of dissection.