. Embryology. Embryology; Embryology; genealogy. INTERVILLOUS PaQ^\ CHORIONIC VILLUS. Fig. 174. Primitive-streak stage in human development. The primitive streak is shown in longitudinal section, and the head process extends forward under the presumptive neural plate. The amnion encloses an amniotic cavity above the blastoderm. Below it a flat sheet of endoderm is continuous with the yolk sac and a small posterior diverticulum is the allantois. Mesoderm surrounds the yolk sac and the amnion and extends around the inner surface of the chorion. The early embryo, amnion, and yolk sac are thus sus
. Embryology. Embryology; Embryology; genealogy. INTERVILLOUS PaQ^\ CHORIONIC VILLUS. Fig. 174. Primitive-streak stage in human development. The primitive streak is shown in longitudinal section, and the head process extends forward under the presumptive neural plate. The amnion encloses an amniotic cavity above the blastoderm. Below it a flat sheet of endoderm is continuous with the yolk sac and a small posterior diverticulum is the allantois. Mesoderm surrounds the yolk sac and the amnion and extends around the inner surface of the chorion. The early embryo, amnion, and yolk sac are thus suspended by a stalk of mesoderm, the body stalk. The outermost extraembryonic membranes have differentiated into a spongy layer, the syntrophoblast, and a compact layer, the chorion. The latter becomes convoluted and together with the mesoderm forms chorionic villi. Blood vessels from the embryo invade the mesoderm within the chorionic villi, and blood sinuses filled with maternal blood develop in the synthrophoblast. 269. 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 Barth, Lester G. (Lester George), 1905-1979. New York, Dryden Press
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