. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. THE DEVELOPMENT OF THE SPINAL CORD. 285 later become penetrated by nerve-fibers that grow from one side to the other. They thus represent the anterior and pos- terior white commissures of the cord. These plates remain relatively fixed in position because of their failure to expand, while the lateral walls of the tube undergo great expansion, in both the ventral and dorsal directions, as well as laterally. In this way a median longitudinal cleft is produced on the ventral wall of the spinal cord
. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. THE DEVELOPMENT OF THE SPINAL CORD. 285 later become penetrated by nerve-fibers that grow from one side to the other. They thus represent the anterior and pos- terior white commissures of the cord. These plates remain relatively fixed in position because of their failure to expand, while the lateral walls of the tube undergo great expansion, in both the ventral and dorsal directions, as well as laterally. In this way a median longitudinal cleft is produced on the ventral wall of the spinal cord and a similar one on the dorsal wall. These are the anterior and posterior median fissures. Since the so-called posterior median fissure is not a true fissure but merely a septum, it differs from the anterior fissure, and it is held by some authorities that this septum is 11 Th ite Do rsa I Do rsa I Ectoderm. matter. commissure. Outer medullary zone. Central canal. Notochord. Ventral commisszire. Pig. 141.—Transverse section of developing spinal cord of a twenty-two-day sheep- embryo (Bonnet). formed by the growing together of the walls of the dorsal part of the central canal. The fiber-tracts or white matter of the spinal cord develop in the outer or neuroglia layer, each fiber being the elongated neurit of a nerve-cell. Some of the fibers originate from the nerve-cells of the cord while others grow into the cord from other sources. As examples of the former method may be cited the direct cerebellar tract, composed of the axons of the cells of the vesicular column of Clark, and the tract of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Heisler, John Clement; Waterstone, David, former owner; Duke-Elder, Stewart, 1898-1978, former owner; University College, London. Library Services. Philadelphia :
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