When formation of the embryo has started it is covered with the amnion membrane (Mohan, Bajaj and Gundappa, 2018). This fills with amniotic fluid enabling the amnion to inflate becoming the amniotic sac delivering a protective environment for the progressing embryo (Mohan, Bajaj and Gundappa, 2018). The amnion, the chorion, the yolk sac and the allantois create a protective sac surrounding the embryo (Mohan, Bajaj and Gundappa, 2018).
The trophoblast creates the external layer of the blastocyst, giving the embryo supplements and giving rise to the external chorionic sac and the fetal part of the placenta (Mohan, Bajaj and Gundappa, 2018). The trophoblast encourages embryonic implantation by means of its inner layer of mononuclear cytotrophoblasts and its external layer of multinuclear cytoplasm, the syncytiotrophoblasts, this makes the early associations between the embryo and the maternal endometrium (Mohan, Bajaj and Gundappa, 2018).
