. The development of the chick; an introduction to embryology. Birds -- Embryology. THE NERVOUS SYSTEM 237 the dorsal root and of the sympathetic system. The first kind only is considered here, and they are usually called the gan- glionic neuroblasts , because they alone remain in the spinal ganglia. Like the medullary neuroblasts these neuroblasts form outgrowths that become axis cylinder processes; but they differ from the latter in that each ganglionic neuroblast forms two axones, one from each end of the spindle-shaped cells, which are arranged with their long axis parallel to the long
. The development of the chick; an introduction to embryology. Birds -- Embryology. THE NERVOUS SYSTEM 237 the dorsal root and of the sympathetic system. The first kind only is considered here, and they are usually called the gan- glionic neuroblasts , because they alone remain in the spinal ganglia. Like the medullary neuroblasts these neuroblasts form outgrowths that become axis cylinder processes; but they differ from the latter in that each ganglionic neuroblast forms two axones, one from each end of the spindle-shaped cells, which are arranged with their long axis parallel to the long axis of the ganglion (Fig. 139). Thus we may distinguish a central process and a peripheral process from each neuroblast, the former grow- ing towards and the latter away from the neural tube (Fig. 139). In other words each ganglionic neuroblast is bipolar, as contrasted w^ith the unipolar medullary neuroblasts. The central axone enters the dorsal zone of the neural tube, and the peripheral one grows out into the surrounding Fig. 141. —Transverse section through the spinal cord of a 9-day chick, prepared by the method of Golgi. (After Ramon y Cajal.) Col., Collaterals, d. R., Dorsal root. G., Gray matter. Gn., Ganglion. Nbl. 4, Neuroblast of the ventral horn (motor), v. R., Ventral root. W., White matter. In the course of the later development the cell-body moves to one side so that the central and peripheral branches appear nearly continuous (Fig. 141). Farther shifting of the cell-body produces the characteristic form of the ganglionic nerve-cell with rounded body provided with stem from which the central and peripheral branches pass off in opposite directions. The central process enters the marginal velum near its dorsal boundary and. 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 Lillie,
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