Found 1 items, similar to yolk sac.
English → English (WordNet) Definition: yolk sac yolk sac n 1: membranous structure that functions as the circulatory system in mammal embryos until the heart becomes functional [syn: 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