Teiary stem villi consists of:-
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.
Central core of cytotrophoblast covered with synctiotrophoblast
Central core of extra-embryonic mesoderm covered by central cyto- and peripheral synctio- trophoblast
Central maternal blood vessels surrounded by mesoderm and trophoblast
Central fetal blood vessels surrounded by mesoderm and trophoblast
Embryology and Histology