. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. METAMORPHOSIS OF THE INTER-BRAIN VESICLE, 297 thickening. The cell-multiplication here is so rapid that each lateral wall is converted into a large ovoid mass of cells with intermingled bands of fibers, the optic thalamus. The roof of the inter-brain vesicle, in notable contrast with the lateral walls, remains extremely thin throughout the greater part of its extent (Fig. 144). From the back part of the roof, at a point immediately in front of the lamina quadrigemina of the mid-brain, a divertic
. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. METAMORPHOSIS OF THE INTER-BRAIN VESICLE, 297 thickening. The cell-multiplication here is so rapid that each lateral wall is converted into a large ovoid mass of cells with intermingled bands of fibers, the optic thalamus. The roof of the inter-brain vesicle, in notable contrast with the lateral walls, remains extremely thin throughout the greater part of its extent (Fig. 144). From the back part of the roof, at a point immediately in front of the lamina quadrigemina of the mid-brain, a diverticulum grows out and becomes metamorphosed into the pineal body. With this exception, the roof of the vesicle remains a single layer of epithelium, just as in the case of the roof of the after- brain. This epithelial layer adheres closely to the pia mater, which covers it in common with the other parts of the brain. As the fore-brain expands, it covers the inter-brain, the under surface of the cerebral hemispheres of the former being closely applied to the roof of the latter. As a con- sequence, the pia mater on the under surface of the fore- Fig. 150.—Brain of fetus of three months, enlarged. The outer wall of the right hemisphere has been removed; LH, left hemisphere; CS, part of corpus striatum ; FS, site of fossa of Sylvius; V, vascular fold of pia mater which has been invag- inated through the mesial wall of the hemisphere; Mb, mid-brain; C, cerebellum; M, medulla oblongata. brain is brought into contact with and adheres to the pia covering the roof of the inter-brain. Thus the thin epithelial roof of the inter-brain becomes closely united with the two layers of the pia mater to form the velum interpositum or tela choroidea anterior or superior of adult anatomy. Ob- viously, the edges of the velum interpositum rest upon the optic thalami, and its piamatral layers are continued into the. Please note that these images are extracted from scanned page images that may have
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