Methacrylate-embedded E19 embryo (medial sagittal)
Figure 98. This medial sagittal slice cuts through the olfactory recess of the lateral ventricle, olfactory NEP, and olfactory SVZ. The characteristic oozing of cells into the ventricle is prominent. The AOB layering is more distinct than on E18. The borders of the mitral cell layer in the MOB are still indistinct as clusters of cells move in from the internal plexiform layer or move out to the external plexiform layer. There are a fair number of tufted cells among the fibers in the external plexiform layer. Note the sharp border between the olfactory nerve/glomerular layer and the external plexiform layer. Spindle-shaped cells appear to be migrating into the ventral MOB near the pial surface in the region of the postulated 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 that is now composed of cartilage; the bone is growing around the already established olfactory nerve bundles. The superficial half of the olfactory epithelium is composed of large olfactory sensory neurons with darkly-staining cytoplasm.