chorionic mesenchymal villus
The first generation of a tertiary villus that is derived from a syncytial sprout by the invasion of the mesenchyme, in which blood vessels differentiate through vasculogenesis, and gradually transforms into a new immature intermediate villus. A chorionic mesenchymal villus has a thick trophoblastic covering, and cytotrophoblast cells are interposed between syncytium and the trophoblastic basal lamina over 50–100% of the surface. The stroma is characterized by loosely arranged collagen fibers that enmesh mesenchymal and some villous macrophages. The fetal capillaries are poorly developed.