Methacrylate-embedded E19 embryo (intermediate horizontal)
Figure 101 is an intermediate horizontal slice through the main olfactory bulb in the same specimen as Figure 100. The lateral migratory stream of mitral cells is prominent; spindle-shaped cells exit the lateral olfactory tract to migrate into the internal plexiform layer where they peel off to join clumps of settling mitral cells (solid curved-line arrows). This slice has well-defined layering in the main olfactory bulb—the mitral cell layer, sandwiched between the cell-sparse external plexiform layer and the internal plexiform layer, has thinned out posteriorly, and clumps are only apparent in the anterior curve. The presumptive anterior olfactory nucleus and the primary olfactory cortex are farther back; the anterior limb of the anterior commissure is prominent and some cells may be migrating forward along its fibers to the anterior olfactory nucleus or to the olfactory bulb itself (dashed-line arrow).