A

David

Darling

trophoblast

The trophoblast is the tissue that forms the wall of the blastocyst. At implantation the trophoblast forms two layers, an inner cellular layer (the cytotrophoblast) and an outer syncytial layer (the syncytiotrophoblast or plasmoditrophoblast), which erodes the maternal tissue and forms the chorionic villi of the placenta.