Cerebellum

The cerebellum develops from the rhombic lip of the metencephalon. Cell proliferation begins in the ventricular zone and then continues in the internal germinal layer (subventricular zone) and the external germinal layer (the most external layer of the marginal zone). The internal germinal layer is the origin of the cells of the cerebellar nuclei as well as the Purkinje, Golgi and stellate cells. The granular cells, which constitute the external granular layer, are formed from the external germinal layer. The external granular layer initially is thick (up to 9 rows of cell bodies). However, it thins out as more and more neurons migrate along the Bergmann glia (a special type of radial glial cell) into the interior of the cerebellum and settle in the internal granular layer. It disappears approximately 6 months after birth. A three-layered cerebellar cortex remains: the molecular layer with only a few cells (outside) followed by a layer of Purkinje cells, and finally the granular cell layer (inside). The Purkinje cells originate from the same cell pool as the neurons of the cerebellar nuclei. During their migration towards the cortex, they maintain contact with the cerebellar nuclei through their axons.