18.2:2 Extra-embryonic membranes include amnion, allantois, chorion, and yolk sac. 1. Amnion: The amnion contains fluid that bathes the embryo, cushions and protects it. 2. Allantois: This membrane gives rise to the urinary bladder; itc ollects embryogenic urine (the nitrogenous waste) produced by the kidneys . 3. The yolk sac: Many blood vessels develop from the yolk sac; it is the first site of blood cell formation.
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4. The chorion forms the fetal half of the placenta; chorionic villi increase the absorptive area of this membrane, and chorionic blood vessels connect with umbilical blood vessels