A membranous appendage of the embryos of mammals, birds, and reptiles, -- in mammals serving to connect the fetus with the parent; the urinary vesicle.
a small, vascularized membrane between the chorion and amnion of the fetus; serves as an early site for blood formation
An extraembryonic membrane of reptiles, birds, and mammals. Saclike outgrowth of tissue that extends outward from the gut of a developing embryo. In mammalian embryos it is situated between the chorion and amnion and functions in respiration, excretion, and nutrition.