Textbook of normal histology: including an account of the development of the tissues and of the organs . e : e, ectoderm invaginated and thickenedwithin neural canal (») ; m, mesoderm ; b, body-cavity; g, still open gut, lined by entoderm (k). THE CENTRAL NERVOUS SYSTEM. ^5 round cells invading the inner zone represent the ancestors of thenervous elements—both cells and fibres—and are the germ-cells,while the columnar cellsproduce the neurogliaand are the spongio-blasts. The development ofthe nerve-cells proceedsfrom the germ-cells,which, as shown by thekaryokinetic figures withintheir nuclei,
Textbook of normal histology: including an account of the development of the tissues and of the organs . e : e, ectoderm invaginated and thickenedwithin neural canal (») ; m, mesoderm ; b, body-cavity; g, still open gut, lined by entoderm (k). THE CENTRAL NERVOUS SYSTEM. ^5 round cells invading the inner zone represent the ancestors of thenervous elements—both cells and fibres—and are the germ-cells,while the columnar cellsproduce the neurogliaand are the spongio-blasts. The development ofthe nerve-cells proceedsfrom the germ-cells,which, as shown by thekaryokinetic figures withintheir nuclei, undergo ac-tive proliferation, theresulting progeny beingthe neuroblasts, fromwhich the nerve - cellsare directly derived. The germ-cells are confined to the zone next the brain-cavity,which thus indicates the position of greatest formative energy. The neuroblasts at first occupy the innermost zone, next thecerebral cavity, but soon migrate towards the outer boundary of thewall, at the same time becoming pyriform and elongated. Theyoung nerve-cells for a long time possess but a single process,. Section of ten-day rabbit embryo, showing closed neuraltube : «, neural canal; s, area from which segmental gan-glia develop ; m, mesodermic tissue ; g, gut-tube ; v, v,primitive aortK ; p, pleuro-pericardial cavity.
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Keywords: ., bookauthorpiersolgeorgeageorgea, bookcentury1800, bookdecade1890
