Fetal Membrances and Surface

Abstract

The peripheral membranes and fetal placental surface are continuous, and most processes are seen in both. The layer of membrane closest to the fetus is amnion. External is the chorion, which is minimal on the peripheral membranes and more extensive on the disk. The remnant of the yolk sac lies between the amnion and chorion (Figure 4.1). The chorion is continuous with all the villous tissue. There is close proximity of the surface membranes to the maternal blood of the intervillous space, while the peripheral membranes abut the decidua and its blood vessels. This relationship permits maternal cells access to the membranes.