This is a specialized cell of the placenta (also a trophoblast) whose function is to attach the baby to the mother's uterus. It provides the anchor. It grows deeply into the lining of the uterus (decidua) and firmly attaches the placenta for the duration of pregnancy.

The cellular (inner) layer of the trophoblast, surrounds the inner all mass.

The cytotrophoblast (or layer of Langhans) is the inner layer of the trophoblast, interior to the syncytiotrophoblast.