The development of the human body; a manual of human embryology . e epithelioid layer, and cover theentire surface of the cerebellum. The cells of this layer, like those of the man-tle, differentiate intoneuroglia cells andneuroblasts, the latterfor the most part mi-grating centrally at alater stage to minglewith the cells of themantle layer and tobecome transformedinto the granular cellsof the cerebellar cor-tex. The neurogliacells remain at the sur-face, however, formingthe principal constitu-ent of the outer or, asit is now termed, themolecular layer of the cortex, and into this the dendrit
The development of the human body; a manual of human embryology . e epithelioid layer, and cover theentire surface of the cerebellum. The cells of this layer, like those of the man-tle, differentiate intoneuroglia cells andneuroblasts, the latterfor the most part mi-grating centrally at alater stage to minglewith the cells of themantle layer and tobecome transformedinto the granular cellsof the cerebellar cor-tex. The neurogliacells remain at the sur-face, however, formingthe principal constitu-ent of the outer or, asit is now termed, themolecular layer of the cortex, and into this the dendrites ofthe Purkinje cells, probably derived from the mantle layer,project. The migration of the neuroblasts of the epithe-lial layer is probably completed before birth, at which timebut few remain in the molecular layer to form the stellatecells of the adult. The origin of the dentate and other nu-clei of the cerebellum is at present unknown, but it seemsprobable that they arise from cells of the mantle nerve-fibers which form the medullary substance of. Fig. 221.—Diagram Representing theDifferentiation of the CerebellarCells. The circles, indifferent cells; circles withdots, neuroglia cells; shaded cells, ger-minal cells; circles with cross, germinalcells in mitosis; black cells, , Lateral recess; M, median furrow,and R, floor of IV, fourth ventricle.—(Schaper.) THE ISTHMUS. 413 the cerebellum do not make their appearance untilabout the sixth month, when they are to be found in theependymal tissue on the inner surface of the layer of gran-ular cells. Those which are not commissural or associa-tive in function converge to the line of junction of thecerebellum with the pons, and there pass into the mar-ginal velum of the pons, myelencephalon, or isthmus asthe case may be. The dorsal surface of the isthmus is at first barely dis-tinguishable from the cerebellum, but as development pro-ceeds its roof-plate undergoes changes similar to thoseoccurring in the
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
