At the end of the fourth week the yolk sac presents the appearance of a small pear-shaped opening ( traditionally called the " umbilical vesicle " ), into the digestive tube by a long narrow tube, the vitelline duct.
परिभाषा
membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional पर्याय: yolk sac, vitelline sac, vesicula umbilicus,
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