The dynamic and directional process that leads neurons from the site of generation in the periventricular proliferative zone to their final location in the cortex is a well-regulated series of events that usually leads the earliest generated neurons to the lower cortex and later generated neurons to the upper cortex. In the process of “radial migration,” immature neurons attach to the fiber of the radial glial cell that produced them, and then crawl along it like an amoeba. Immature neurons then arrive in the developing brain in successive waves and form the characteristic layers of the cerebral cortex, with each successive wave rolling through the previous one. Not all cells migrate in this manner. The granular cells of the cerebellum are produced by a structure called the rhombic lip, located at the edge of the opening of the roof of the neural tube. Immature granular neurons leave the rhombic lip and move to the outer surface of the neural tube, after which they unfold and migrate to the developing cerebellum.