Figure 3.

Embryonic Development of the Cerebral Cortex. The ventricular zone (VZ) contains proliferating progenitors of neurons and glia (blue mitotic cells). The first postmitotic, neuronal precursors move above the VZ where they settle in a narrow zone, the preplate (PP). Preplate neurons pioneer cortical axons to both cortical and sub-cortical targets. In-growing axons establish the intermediate zone (IZ). After E13, the preplate splits into the marginal zone (MZ), or future layer I, which contains Cajal-Retzius cells, and the subplate (SP), a transient population of neurons. By E16, the cortical plate thickens as precursors of large, output neurons (orange cells), as well as of some interneurons, migrate along radial glia (navy cells) to establish the neuronal layers. A large population of interneurons (green cells), nearly 80% in the developing murine neocortex, migrate into the developing cortex from the basal forebrain in a trajectory that is tangential to the radial plane. These neurons migrate into the emerging cortical laminae along axons in the IZ and the MZ. Neurogenesis (blue and yellow mitotic cells) continues in both the VZ and the subventricular zone (SVZ), a zone of dividing cells above the VZ which generates neuronal precursors that migrate rostrally, forming the rostral migratory stream.