The amnion is the innermost membrane surrounding the amniotic cavity filled with fluid. It protects the embryo from drying out and shock. The chorion is the outermost membrane that forms the placenta connecting the mother and child. It has chorionic villi. The allantois and yolk sac are lower membranes that are part of the umbilical cord, with the allantois helping excretion and the yolk sac supplying nutrition to the embryo. The extra embryonic membranes form from the three germ layers, with the ectoderm forming the amnion, mesoderm forming somatic and splanchnic layers, and endoderm folding to form structures like the yolk sac and all

1. AMNION
 Innermost extra embryonic membrane.
 Made of ectoderm and somatic mesoderm.
 Surround amniotic cavity which is filled with amniotic
fluid.
 It continuously keep the embryo wet and don’t let it dry.
 It protect the embryo from shock.
 Amniotic fluid is taken for amniocentesis.

2. CHORION
 Outermost extra embryonic membrane.
 Made of tropoblast and somatic mesoderm.
 Has chorionic villi.
 Form placenta to connect mother and child.

3. ALLANTOIS
 Allantois is a lower side extra embryonic membrane.
 It is formed of endoderm and splanchnic
mesoderm.
 It is a part of umbilical cord.
 It helps in excretion of the embryo.

4. YOLK SAC
 Yolk sac is one lower side extra embryonic
membrane.
 It is formed of endoderm and splanchnic
mesoderm.
 It is a part of umbilical cord.
 It supply nutrition to the embryo.

5. FORMATION OF EXTRA EMBRYONIC MEMBRANE
 Three germ layers are ecto,meso and endoderm.
 Ectoderm expand to form amniotic cavity.
 Middle mesoderm fold to form somatic and splanchnic mesoderms.
 Somatic mesoderm cover the amniotic ectoderm.
 Further somatic mesoderm cover the amnion with a space called extra embryonic coelom below
trophoblast.
 Endoderm fold to form the embryonic gut, yolk sac and allantois.
 Splanic mesoderm cover the yolk sac and allantois.