The development of the human body; a manual of human embryology . e and of an elongated oval form, butlater it becomes somewhat rhomboidal in shape (Fig. 215,A), the lateral angles marking the boundaries between thedorsal and ventral zones. As development proceeds thesides of the canal in the dorsal region gradually approachone another and eventually fuse, so that this portion ofthe canal becomes obliterated (Fig. 215, B) and is indi-cated by the dorsal longitudinal fissure in the adult cord,the central canal of which corresponds to the ventral por-tion only of the embryonic cavity. While this
The development of the human body; a manual of human embryology . e and of an elongated oval form, butlater it becomes somewhat rhomboidal in shape (Fig. 215,A), the lateral angles marking the boundaries between thedorsal and ventral zones. As development proceeds thesides of the canal in the dorsal region gradually approachone another and eventually fuse, so that this portion ofthe canal becomes obliterated (Fig. 215, B) and is indi-cated by the dorsal longitudinal fissure in the adult cord,the central canal of which corresponds to the ventral por-tion only of the embryonic cavity. While this process hasbeen going on both the roof- and the floor-plate have be-come depressed below the level of the general surface of 34 4o: THE DEVELOPMENT OF THE HUMAN BODY. the cord,, and by a continuance of the depression of thefloor-plate—a process really due to the enlargement andconsequent bulging of the ventral zone—the ventral fis-sure is produced, the difference between its shape and thatof the dorsal fissure being due to the difference in Fig. 215.—Transverse Sections through the Spinal Cords op Em-bryos of (.4) about Four and a Haep Weeks and (B) aboutThree Months. cB, Column of Burdach; cG, column of Goll; dh, dorsal horn; dz, dorsalzone; fp, floor-plate; ob, oval bundle; rp, roof-plate; vk, ventral horn;vz, ventral zone.—(His.) The development of the mantle layer proceeds at firstmore rapidly in the ventral zone than in the dorsal, so thatat an early stage (Fig. 215, A) the anterior horn of graymatter is much more pronounced, but on the developmentof the dorsal nerve-roots the formation of neuroblasts inthe dorsal zone proceeds apace, resulting in the formation THE SPINAL CORD. 403 of a dorsal horn. A small portion of the zone, situatedbetween the point of entrance of the dorsal nerve-rootsand the roof-plate, fails, however, to give rise to neuro-blasts and is entirely converted into ependyma. Thisrepresents the future column of Goll (Fig. 4s©, A
Size: 1853px × 1349px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
