{ ‖ } n.. (Anat.) A membranous appendage of the embryos of mammals, birds, and reptiles, -- in mammals serving to connect the fetus with the parent; the urinary vesicle. [ 1913 Webster ]
‖n. pl. [ NL. ] (Zool.) The division of Vertebrata in which the embryo develops an allantois. It includes reptiles, birds, and mammals. [ 1913 Webster ]