E13+14 to P5 (ANTERIOR)
By P5, cell populations have settled in the olfactory peduncle and in the main olfactory bulb virtually identical to the appearance of the bulb and peduncle in the mature brain. Figure 4 is an anterior coronal slice of the main olfactory bulb in front of the olfactory recess of the lateral ventricle. The accessory olfactory bulb is not in this slice. Nearly all cells are labeled in the mitral cell layer, internal and external plexiform layers indicating that these neurons were generated after 3H‑thymidine injections started on E13. The granule cell layer is full of apparently unlabeled cells, but that is because these neurons are generated much after E13 so the label is no longer detectable. The tiny spindle shaped cells in the core of the bulb are migrating cells associated with the rostral migratory stream; many of these cells are generated after birth; again, there is no detectable label.