Textbook of normal histology: including an account of the development of the tissues and of the organs . pends upon the special-ization of the columnar elements, thespongioblasts. The epithelial cellselongate, their protoplasm at the sametime undergoing vacuolation andpartial absorption, resulting in theproduction of an elongated frameworkof connected slender trabeculae. Theextremities of the changed epithelialelements, or spongioblasts, greatly dif-fer ; the inner ends of the cells extendto the inner boundary, where they areunited to form a continuous sheet, themembrana limitans interna, and
Textbook of normal histology: including an account of the development of the tissues and of the organs . pends upon the special-ization of the columnar elements, thespongioblasts. The epithelial cellselongate, their protoplasm at the sametime undergoing vacuolation andpartial absorption, resulting in theproduction of an elongated frameworkof connected slender trabeculae. Theextremities of the changed epithelialelements, or spongioblasts, greatly dif-fer ; the inner ends of the cells extendto the inner boundary, where they areunited to form a continuous sheet, themembrana limitans interna, and theouter processes break up into irregularbranches, which ultimately form a closereticulum. The early spongioblasts ex-tend the entire thickness of the neuralwall, but with the subsequent increase inthis structure their attachments becomebroken, the spongioblasts then lying freeamong the surrounding nervous general growth of the tissues is ac-companied by great extension and sub-division of the neuroglia fibres, whicheventually become the nucleated masses of fine, bristle-like processes. Spongioblasts from neural tube;their expanded upper ends unite toconstitute the internal limiting mem-brane next the brain-cavity ; theirouter ends break up into reticulum.(After His.) THE CENTRAL NERVOUS SYSTEM. ^,r constituting Deiterss or spider cells. The spongioblasts im-mediately around persistent parts of the neural canal retain theirinner connection and form a continuous layer of lining elements,which later constitute the ciliated columnar epithelium of theependyma. The development of the nerve-fibres includes the origin oftwo sets of primary fibres—those derived from the nerve-cellsof the medullary tube and those growing out from the cells ofthe ganglia. All nerve-fibres are formed as the direct exten-sions and continuations of the processes of the the case of those proceeding from the neural canal the fibresgrow peripherally and the cells remain attached
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Keywords: ., bookauthorpiersolgeorgeageorgea, bookcentury1800, bookdecade1890
