Methacrylate-embedded E20 embryo in the horizontal plane (ventral)
Figure 118. This ventral horizontal slice from the same specimen in Figures 116 and 117 clearly shows the fan-like array of migrating mitral cells in the tangentially cut internal plexiform layer. Mitral cells leave their axons behind in the lateral olfactory tract and head toward the mitral cell layer (solid-line curved arrows) that occupies the lateral, anterior, and medial edges of the bulb, beneath the cell-sparse external plexiform layer. Note that the external plexiform layer has quite a few tufted cells that appear as superficially-placed mitral cells; there are some smaller cells in between the whorls of fibers. The dense small cells behind the internal plexiform layer are either in the SVZ or the future MOB granule cell layer. The anterior olfactory nucleus is tentatively identified in the olfactory peduncle, in front of the primary olfactory cortex on the lateral side of the brain. Migrating cells stretching across the peduncle can go in either direction, some medial, others lateral (broken line arrow).