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DEVELOPMENT OF THE CEREBELLUM
The cerebellum develops from the dorsolateral part of the alar lamina of the metencephalon (Fig. 7.5A). Obviously, there are at first two primordia of the cerebellum, right and left. These extend medially in the roof plate of the metencephalon to eventually fuse across the midline (Figs. 7.5B, C). As the cerebellum increases in size, fissures appear on its surface. The lateral lobes and vermis can soon be distinguished, as a result of differential growth.
The developing cerebellum can be divided into: (a) an intraventricular part that bulges into the cavity of the developing fourth ventricle, and (b) an extraventricular part that is seen as a bulging on the surface (Fig. 7.5C). At first the intraventricular part is the larger of the two, but at a later stage, the extraventricular part becomes much larger than the intraventricular part and constitutes almost the whole of the organ (Fig. 7.5D).
The cerebellum, at first, consists of the usual matrix cell, mantle and marginal layers. Some cells of the mantle layer migrate into the marginal layer to form the cerebellar cortex. The cells of the mantle layer that do not migrate into the cortex, develop into thedentate, emboliform, globose and fastigalnuclei.
The superior cerebellar peduncle is formed chiefly by the axons growing out of the dentate nucleus. The middle cerebellar peduncle is formed by axons growing into the cerebellum from the cells of the pontine nuclei, while the inferior cerebellar peduncleis formed by fibres that grow into the cerebellum from the spinal cord and medulla.
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