Teiary stem villi consists of:-: (A) Central core of cytotrophoblast covered with synctiotrophoblast, (B) Central core of extra-embryonic mesoderm covered by central cyto- and peripheral synctio- trophoblast, (C) Central maternal blood vessels surrounded by mesoderm and trophoblast, (D) Central fetal blood vessels surrounded by mesoderm and trophoblast
Answer is D. Secondary villi:- contains a central core of primary (extra embryonic) mesoderm and is covered by cyto- and syncytio- trophoblast cells. Teiary villicontains fetal blood vessels invading the extra embryonic mesoderm and is covered by trophoblastic cells.