Human Embryology and Teratology
Teaching text 18: Formation of the placenta 5: Anchoring villi
Cytotrophoblast cells of the villi break through the syncytial layer in several places and spread between this layer and the decidua. An external cytotrophoblastic shell (the early basal plate) arises, which surrounds the entire trophoblast. The mesenchymal villous cores then lengthen and become anchored to the decidua as anchoring villi. They connect the chorionic plate with the basal plate.