Methacrylate-embedded E19 embryo (dorsal horizontal)
Figure 100 is the dorsal horizontal slice through the accessory part of the olfactory bulb in an E19 specimen, much like the E18 specimen in Figure 84. The slice cuts through the ventral limits of the cortical plate laterally and through the transitional NEPs of the neocortex, septum, and striatum; the slice is above the olfactory NEP. The horizontal cutting plane is always the best to show migration streams, and many spindle-shaped cells appear to be migrating toward the settling AOB output neurons (curved solid-line arrows). The dashed-line arrow traces a more tentative migratory stream coming into the AOB from a deep position anterior to the infralimbic or dorsal peduncular cortex. The double-ended arrow traces a prominent migratory stream that forms a cap around layer 1 in the orbital cortex; these cells may be migrating in both directions—lateral to medial and medial to lateral. A prominent stream of spindle-shaped cells (outlined by dashed lines) is migrating out of the transitional NEP between the cortical and striatal NEPs; the stream appears to penetrate fibers of the stratified transitional field in the neocortex.