Fig. 1 Schematic drawing of the full-term tammar fetus and fetal membranes. All, allantois; Amn, amnion; AYS, avascular yolk sac; BOm, bilaminar omphalopleure (yolk sac); Ch, chorion; ST, sinus terminalis; TOm, trilaminar omphalopleure (yolk sac); VYS, vascular yolk sac.