yolk sac vitelline sac umbilical vesicle vesicula umbilicus
yolk_sac%1:05:02:: vitelline_sac%1:05:00:: umbilical_vesicle%1:05:00:: vesicula_umbilicus%1:05:00::
membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional