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Methacrylate-embedded E17 embryo (lateral sagittal)

Figure 66.  This sagittal slice is from the same specimen shown in Figure 65, only it cuts through the lateral olfactory bulb, the anterolateral basal ganglionic NEP, and the posteromedial basal ganglionic NEP.  The anterolateral basal ganglionic NEP is an “peninsula” over the other basal telencephalic structures projecting into the lateral ventricle.  The expanding olfactory bulb has recognizable layers: most deep, the densely-packed columnar NEP cells, next the SVZ with less dense cells in a variety of orientations, next the internal plexiform layer of both the MOB and AOB.  A cluster of rounded cells in the dorsal bulb are settling AOB output neurons.  Discontinuous clusters of large cells with dense cytoplasm are pioneer mitral cells setting up the layer at the perimeter of the internal plexiform layer.  Just beneath the obliterated brain surface is a thin fibrous layer—the external plexiform layer.  Coalesced fiber bundles of the olfactory nerve surround the growing bulb and form a thick nerve beneath it.  Note that the nerve fibers are growing through the differentiating cribriform plate of the ethmoid bone.  Individual bundles of the olfactory nerve are growing in between the undulations of the olfactory epithelium in the superior nasal cavity.