The development of the human body; a manual of human embryology . anches continuing ven-trally in the body-wall, while the other (Fig. 234, wr) passesmesially toward the aorta, some of its fibers reaching thatstructure, while others bend so as to assume a longitudinaldirection. These mesial branches represent the whiterami communicantes, but as yet no ganglion cells can beseen in their course. The cells of the posterior rootganglia have already, for the most part, assumed theirbipolar form, but among them there may still be found anumber of cells in the neuroblast condition, and these(Fig. 234
The development of the human body; a manual of human embryology . anches continuing ven-trally in the body-wall, while the other (Fig. 234, wr) passesmesially toward the aorta, some of its fibers reaching thatstructure, while others bend so as to assume a longitudinaldirection. These mesial branches represent the whiterami communicantes, but as yet no ganglion cells can beseen in their course. The cells of the posterior rootganglia have already, for the most part, assumed theirbipolar form, but among them there may still be found anumber of cells in the neuroblast condition, and these(Fig. 234, s), wandering out from the ganglia, give rise toa column of cells standing in relation to the white first there is no indication of a segmental arrangement THE SYMPATHETIC SYSTEM. 445 of the cells of the column (Fig. 235), but at about theseventh week such an arrangement makes its appearancein the cervical region, and later, extends posteriorly, untilthe column assumes the form of the ganglionated , however, the segmentation becomes marked,. Fig. 234.—Transverse Section through the Spinal Cord of an Em-bryo op 7 , Notochord; g, posterior root ganglion; m, spinal cord; s, sympathetic cell migrating from the posterior root ganglion; wr, white ramus.— (His.) thickenings appear at certain regions of the cell column,and from these, bundles of fibers may be seen extendingventrally toward the viscera. The thickenings representcertain of the prevertebral ganglia, and later cells wanderout from them and take a position in front of the aorta. 446 THE DEVELOPMENT OF THE HUMAN BODY. In an embryo of mm. two ganglionic masses ( Pc) occur in the vicinity of the origin of the omphalo-mesenteric artery {am), one lying above and the otherbelow that vessel; these masses represent the ganglia ofthe solar plexus and have separated somewhat from theganglionated cord, the fiber bundles which unite the uppermass with the cord representing the greater and lesse
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
