Meaning of yolk sac
— Embryol. Embryol.
- an extraembryonic membrane that encloses the yolk of eggs in birds, reptiles, and marsupials and that circulates nourishment from the yolk to the developing embryo.
- a similar membrane in placental mammals that encloses a mostly hollow space and loses its nutritive function entirely as the placenta develops.
- yolk sac (Thesaurus)