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Methacrylate-embedded E19 embryo (ventral horizontal)

Figure 102.  This ventral horizontal slice from the same specimen in Figures 100 and 101 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 and some smaller cells in between the whorls of fibers.  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 (double-ended broken line arrow).