. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. THE CEREBELLUM 393 the brain (Fig. 236, B), the roof-plate probably being invaded by cells from the dorsal zones and so giving rise to the vermis, while the lobes are formed directly from the dorsal zones. During the second month a groove appears on the ventral surface of each lobe, marking out an area which becomes the flocculus, and later, during the third month, transverse furrows appear upon the vermis dividing it into five lobes, and later still extend out upon the lobes and increase in
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. THE CEREBELLUM 393 the brain (Fig. 236, B), the roof-plate probably being invaded by cells from the dorsal zones and so giving rise to the vermis, while the lobes are formed directly from the dorsal zones. During the second month a groove appears on the ventral surface of each lobe, marking out an area which becomes the flocculus, and later, during the third month, transverse furrows appear upon the vermis dividing it into five lobes, and later still extend out upon the lobes and increase in number to produce the lamel- late structure characteristic of the cerebellum. The histogenetic develop- ment of the cerebellum at first proceeds along the lines which have already been described as typical, but after the devel- opment of the mantle layer the cells lining the greater portion of the cavity of the ventricle rease to rrmltinlv onlv those FlG- 237-—Diagram Representing the cease to multiply, oniy tnose DifferenTiation of the Cerebellar Cells. which are situated in the roof- The circles, indifferent cells; circles with plate of the metencephalon d°f' n shaded c?lls: g™.al 1 r cells; circles with cross, germinal cells in and along the line of junction mitosis; black cells, nerve-cells. L, Lateral . , , ,, ,i • i • recess; M, median furrow, and R, floor of IV, of the cerebellar thickening fourth ventricle.—(Schaper.) with the roof-plate continuing to divide. The indifferent cells formed in these regions migrate outward from the median line and forward in the marginal ve- lum to form a superficial layer, known as the epithelioid layer, and cover the entire surface of the cerebellum (Fig. 237). The cells of this layer, like those of the mantle, differentiate into neuroglia cells and neuroblasts, the latter for the most part migrating centrally at a later stage to mingle with the cells of the mantle layer and to become transformed into the granular cells of the
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