常见例句The yolk sac is gradually vascularized.卵黄囊逐渐被血管化了。The gonads form from a group of large granulated yolk sac cells which invacle the germinal ridges.性腺是由一群大的颗粒的卵黄囊细胞入缀生殖峭而形成。 返回 vitelline sac