. A laboratory manual and text-book of embryology. Embryology. 3i4 HISTOGENESIS to a position between the neural tube and myotomes. In this position the ganglion crest forms a band of cells extending the whole length of the spinal cord and as far cranially as the otic vesicles. At regular intervals in its course along the spinal cord the proliferating cells of the crest give rise to enlargements, the spinal ganglia (Fig. 340). The spinal ganglia are segmentally arranged and con- nected at first by bridges of cells which later disappear. In the hind-brain region certain ganglia of the cerebral
. A laboratory manual and text-book of embryology. Embryology. 3i4 HISTOGENESIS to a position between the neural tube and myotomes. In this position the ganglion crest forms a band of cells extending the whole length of the spinal cord and as far cranially as the otic vesicles. At regular intervals in its course along the spinal cord the proliferating cells of the crest give rise to enlargements, the spinal ganglia (Fig. 340). The spinal ganglia are segmentally arranged and con- nected at first by bridges of cells which later disappear. In the hind-brain region certain ganglia of the cerebral nerves develop from the crest but are not seg- mentally Eig. 302.—Three stages in the development of the ganglion crest in human embryos (after von Lenhossek in Cajal). a, ectoderm; b, neural tube; c, mesodermal segment; G, ganglioblasts. The Differentiation of the Afferent Neurones.—The cells of the spinal ganglia differentiate into (1) ganglion cells and (2) supporting cells, groups which are comparable to the neuroblasts and spongioblasts of the neural tube. The neuro- blasts of the ganglia become fusiform, develop a primary process at either pole and thus these neurones are of the bipolar type. The centrally directed processes of the ganglion cells converge and by elongation form the dorsal roots. They penetrate the dorso-lateral wall of the neural tube, bifurcate and course cranially and caudally in the marginal layer of the spinal cord (Fig. 300, d). By means of branched processes they anastomose with the neurones of the mantle layer. The peripheral processes of the ganglion cells as the dorsal spinal roots join the ventral. 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 Prentiss, Charles William, 1874-1915. Philadelphia, London, W. B. Saunders
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