umbilical vesicle(n = noun.animal) vesicula umbilicus, vitelline sac, yolk sac - membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional;
is a kind of sac

blastodermic vesicle, seminal vesicle, umbilical, umbilical cord, umbilical hernia, umbilical vein, vesicle