Quain's elements of anatomy . ite the third en-cephalic vesicle; am, the cephalic foldof the amnion ; or, the vitelline veinsentering the heart posteriorly; fv, theprotovertebral somites. But it is not yet fully ascertained whether the whole of the peripheralnerves are derived from this source or are formed by secondary differen-tiation from blastema in the more remote seats of their origin. From what has been previously stated it will have been seen that therudiment of the cerebro-spinal nervous centre is formed more immedi-ately from the thickened medullary plates of the involuted epiblast,
Quain's elements of anatomy . ite the third en-cephalic vesicle; am, the cephalic foldof the amnion ; or, the vitelline veinsentering the heart posteriorly; fv, theprotovertebral somites. But it is not yet fully ascertained whether the whole of the peripheralnerves are derived from this source or are formed by secondary differen-tiation from blastema in the more remote seats of their origin. From what has been previously stated it will have been seen that therudiment of the cerebro-spinal nervous centre is formed more immedi-ately from the thickened medullary plates of the involuted epiblast, theridges of which, rising from the surface of the blastoderm, become uniteddorsally along the middle line so as to close in a hollow medullary tube ofa cylindrical form. This tube is wider at its anterior or cephalic extre-mity, and this dilated portion becomes divided by partial constrictions,first into two, and very soon after into three primary cerebral orencephalic vesicles, which represent anterior, middle and posterior.
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Keywords: ., boo, bookcentury1800, booksubjectanatomy, booksubjecthumananatomy
