Quain's elements of anatomy . bral bodies; al, alimentary canal. as held by Remak, in more or less immediateconnection with the parts of mesoblasticorigin in which they were distributed. Theonly known fact inconsistent with this ^dewwas that the anterior or motor roots of thesj^inal nerves had been found to bud out fromthe ventral side of the spinal cord. Therecent researches especially of His, Balfour,and Marshall, Kolliker, Hensen and others,have thrown quite a new light on this subject, and have shown that allthe peripheral nerves, cerebro-spinal and sympathetic, with their ganglia,emanate
Quain's elements of anatomy . bral bodies; al, alimentary canal. as held by Remak, in more or less immediateconnection with the parts of mesoblasticorigin in which they were distributed. Theonly known fact inconsistent with this ^dewwas that the anterior or motor roots of thesj^inal nerves had been found to bud out fromthe ventral side of the spinal cord. Therecent researches especially of His, Balfour,and Marshall, Kolliker, Hensen and others,have thrown quite a new light on this subject, and have shown that allthe peripheral nerves, cerebro-spinal and sympathetic, with their ganglia,emanate originally from the primary brain and spinal marrow, that theyhave therefore an epiblastic origin, and that they spread more or less fromthence into the different parts of the body. (See Nos. 28 and 202—205.)Spinal Herves.—Following the description of their origin given byBalfour and Marshall, it may be stated that the posterior roots of the spinalnerves and most of the cranial nerves, with their respective ganglia, which. THE SPINAL NEHVES. 837 are formed before tlie anterior roots, proceed from a series of cellularswellings, constituting the neural crest, which are in continuity with themeduUary plates close to the place of inflection of the epiblast into theinvolution which forms the primary brain and spinal cord. These rootswellings are in some animals connected together by a longitudinal bandor commissure. In the primitive projections there are soon distinguisheda narrower first part or root, then a tliicker part, the ganglion, andfmther down a part of the nerve extending beyond it. The root origi-nally connected with the upper part of the medullary wall close to themedian line slips down, as it were, upon the side, and is subsequently Fig. 743.—Section through ^^° ^^* THE DORSAL PART OF THETRUNK OF A TORPEDO EM-BRYO. (From Balfour.) pr, posterior root of spinalnerve ; g, spinal ganglion ;n, nerve ; ar, anterior root ;ch, notochord; nc, neuralcanal; »!p, muscle-pla
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