. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. THE DEVELOPMENT OF THE BRAIN. 289 ventral wall of the secondary hind-brain, is a second well- marked angularity. This is the pontal flexure. Its con- vexity projects forward. A third bend, the nuchal flexure, is a less pronounced curvature at the juncture of the after-brain with the spinal part of the neural tube. The Metamorphosis of the Fifth Brain-vesicle.— The fifth brain-vesicle, the caudal division of the primary hind-brain, differentiates into the structures which surround the lower half
. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. THE DEVELOPMENT OF THE BRAIN. 289 ventral wall of the secondary hind-brain, is a second well- marked angularity. This is the pontal flexure. Its con- vexity projects forward. A third bend, the nuchal flexure, is a less pronounced curvature at the juncture of the after-brain with the spinal part of the neural tube. The Metamorphosis of the Fifth Brain-vesicle.— The fifth brain-vesicle, the caudal division of the primary hind-brain, differentiates into the structures which surround the lower half of the fourth ventricle, these structures con-. Fig. 144.—Diagram of a sagittal section of the brain of a mammal, showing the type of structure and the parts that develop from the several brain-vesicles (modified from Edinger). stituting the myelencephalon (Fig. 144). The histological changes correspond essentially with those that occur in the spinal segment of the neural tube, the nerve-cells and fibers and the neuroglia resulting from the differentiation of the original ectodermic epithelium of which the wall of the tube is composed, and the connective-tissue stroma growing into these from the surrounding mesoderm. There is a marked disproportion between the rate of growth of the tube in different parts of its circumference. The great thickening of the ventral and lateral walls produces the several parts of the medulla oblongata. In the dorsal wall 19. 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 : W. B. Saunders Company
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