Yolk sac and allantois · Yolk sac(卵黄囊) Respiratory Primitive gut Heart Liver bud 3rd week, Germ Cells Duodenum duct 3rd to 6th week Allantois-fE Blood island Hindgut 地Gog吨w Al| antos(尿囊) The placenta and the Umbilical cord Caudal extension of hindgut Uterus Allantoic A pairs Umbilical cord Bood Umbilical Allantoic V pairs arteries Connecting Umbilical cord Umbilical chorion Umbilical vessels veIn Placenta Fetal portion Maternal of placenta portion of 2A+1V placentaYolk sac and Allantois • Yolk sac（卵黄囊） – Primitive Gut – 3 rd week, Germ Cells – 3 rd to 6th week, Blood island • Allantois（尿囊） – Caudal extension of hindgut – Allantoic A pairs – Allantoic V pairs Umbilical vessels 2A+1V