1. 鳥、爬虫類、有袋動物とある魚類の卵黄を包む脊椎組織(membranous structure enclosing the yolk of eggs in birds, reptiles, marsupials, and some fishes)
2. 心臓が機能するまでに哺乳動物の胎児の循環器官として機能する膜構造(membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional)