yolk sac

汉语翻译

英语解释：

名词 yolk sac:

1. membranous structure that functions as the circulatory system in mammal embryos until the heart becomes functional
   同义词：vitelline sac, umbilical vesicle, vesicula umbilicus
2. membranous structure enclosing the yolk of eggs in birds reptiles marsupials and some fishes; circulates nutrients to the developing embryo