part_of part of part of has_part has part has part develops_from develops from develops from has developmental contribution from has developmental contribution from cloaca endoderm renal system allantois A membranous sac that develops from the posterior part of the alimentary canal in the embryos of mammals, birds, and reptiles, and it is important in the formation of the umbilical cord and placenta in mammals[VHOG]. allantoic bud splanchnic layer of lateral plate mesoderm extraembryonic membrane