membranous structure that functions as the circulatory system in mammal embryos until the heart becomes functional
同义词：yolk sac??/??vitelline sac??/??vesicula umbilicus
英汉双解词典包含3185865条英汉词条，基本涵盖了全部常用单词的翻译及用法，是英语学习的有利工具。