Mode of cell migration to the superficial layers of fetal monkey neocortex

Golgi and electronmicroscopic methods were used to define the shapes and intercellular relationships of cells migrating from their sites of origin near the ventricular surface across the intermediate zone to the superficial neocortical layers of the parietooccipital region in the brains of 75‐ to 97‐day monkey fetuses. After mitotic division in either ventricular or subventricular zones, the cells enter the intermediate zone and assume an elongated bipolar form oriented toward the cortical plate. The leading processes, 50 to 70 μ long, are irregular cytoplasmic cylinders containing prominent Golgi apparatus, mitochondria, microtubules, ribosomal rosettes, immature endoplasmic reticulum and occasional centrioles. They usually terminate in several attenuated expansions, the longest one oriented toward the cortical plate. The trailing processes are more slender, relatively uniform in caliber and display few organelles.