yolk sac

Từ điển WordNet v3.1 - WordNet Dictionary

noun

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