yolk_sac
1. [ noun ] (anatomy,zoology) membranous structure that functions as the circulatory system in mammal embryos until the heart becomes functional
Synonyms: vesicula_umbilicus vitelline_sac umbilical_vesicle
Related terms: sac
2. [ noun ] (anatomy,zoology) membranous structure enclosing the yolk of eggs in birds reptiles marsupials and some fishes; circulates nutrients to the developing embryo
Related terms: sac