. Analysis of development. Embryology; Embryology. ^y^ ^i =^^^7""^ W-^^ K^ ] ^^k ^MXf >-N 'S It ''^^^^ M^'^ ^s Fig. 138. Shape of neural tube under different conditions (from Holtfreter, '34). A, Solid neural mass developed in explantation: nuclei of gray matter crowded near the surface; white matter in the interior. B, Neural tube surrounded by mesenchyme: shape cylindrical with central lumen; nuclei massed at the inner (free) surface. C, As5Titaxia dorsalis (failure of the tube to close); thinning of the floor of the tube in contact with the notochord; gray matter along the free
. Analysis of development. Embryology; Embryology. ^y^ ^i =^^^7""^ W-^^ K^ ] ^^k ^MXf >-N 'S It ''^^^^ M^'^ ^s Fig. 138. Shape of neural tube under different conditions (from Holtfreter, '34). A, Solid neural mass developed in explantation: nuclei of gray matter crowded near the surface; white matter in the interior. B, Neural tube surrounded by mesenchyme: shape cylindrical with central lumen; nuclei massed at the inner (free) surface. C, As5Titaxia dorsalis (failure of the tube to close); thinning of the floor of the tube in contact with the notochord; gray matter along the free surface. D, Neural tube underlain by muscula- ture; lumen eccentric at far side; white matter at near side. E, Neural tube underlain by notochord; normal appearance; slit-shaped lumen, oriented towards notochord. /, Limien; m, mesenchyme; c, noto- chord; s, segmented musculature. transient incompatibility (or disaffinity) be- tween the two groups. Thus, visible move- ments and shaping processes appear as the observable results of more intimate physico- chemical distinctions within the prospective neural system. Early Morphogenesis of Brain and Cord. The gross shapes of the early brain and cord, respectively, are anticipated in the proportions of the neural plate, whose wide anterior part, upon folding upward, forms the large vault of a brain ventricle, while the narrower posterior part encloses the narrow lumen of the central canal of the spinal cord. The shape of the canal varies with the details of the folding process (Fig. 138). Uni- form curling of the plate would leave a holds the midline firmly anchored as a hinge about which the flanks of the plate fold up (Weiss, '50c). A similar fibrous plane seems to define the border between the alar and basal plate cell masses; as the latter grow and bulge, it gives rise to the lateral sulcus. Because of their importance for the later regular distribution and group- ing of cell cokmins, svich tangible traces of early subdivisions w
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
