. Elements of physiological psychology; a treatise of the activities and nature of the mind, from the physical and experimental points of view . Neural groove(.still unclosed) Fio. 11.—Dorsal View of a Human Embryo, Some-what More Advanced than the Preceding. (Eter-nod.) About i. The neural groove has closed toa tube in the middle of its extent, but is still openat the cerebral and lumbar ends. 40 THE NERVOUS SYSTEM IN THE INDIVIDUAL specialized condition. The process by which this tube of undiffer-entiated cells becomes a cord of nervous tissue is as follows. Inthe wall of the tube next to th
. Elements of physiological psychology; a treatise of the activities and nature of the mind, from the physical and experimental points of view . Neural groove(.still unclosed) Fio. 11.—Dorsal View of a Human Embryo, Some-what More Advanced than the Preceding. (Eter-nod.) About i. The neural groove has closed toa tube in the middle of its extent, but is still openat the cerebral and lumbar ends. 40 THE NERVOUS SYSTEM IN THE INDIVIDUAL specialized condition. The process by which this tube of undiffer-entiated cells becomes a cord of nervous tissue is as follows. Inthe wall of the tube next to the cavity or lumen some cells be-come reproductively active, and divide, giving rise to daughter cells,which move away toward the outside of the wall, but stop midway,and proceed to change their form, sending out branches that Germinal Marginal _,layer Neural Fig. 12.—Cross Section of the Neural Tube and Crests of a Human Embryo of about FiveWeeks. (His.) The dorsal side is uppermost in the figure. Many facts which are men-tioned in the text can be observed in this figure. The three layers of the tube are readilydistinguished: the germinal layer, next to the lumen of the tube, is dark with its closelypacked cells. The nerve-cell layer, outside of this, is more loosely packed, while the mar-ginal layer is free from cells. The fact that the nerve-cell layer develops to the sides,and not directly in the mid-ventral and mid-dorsal lines, is evident. _ Commissural axons,crossing at the mid-ventral line, can be observed; also axons passing into and out of thetube in the dorsal and ventral roots. The neural crest is clearly distinguished from thesurrounding tissues in the left side of the figure. A streaky appearance in the crest indi-cates the direction of the growing axons toward the dorsal root. Within the tube, close
Size: 1945px × 1284px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., boo, bookcentury1900, bookdecade1910, booksubjectpsychophysiology
