Final answer:
When two fetal membranes adhere, they form the chorionic membrane, which develops into the chorion, integral in forming the fetal side of the placenta through the chorionic villi.
Step-by-step explanation:
Two fetal membranes, when they adhere, form the chorionic membrane, which is a precursor to the chorion. The chorion is significant in fetal development as it surrounds the embryo and, through the chorionic villi, forms the fetal portion of the placenta. The chorionic villi are projections of the chorionic membrane that penetrate the uterine lining, crucial for nutrient and gas exchange between mother and fetus.
The chorion is comprised of the syncytiotrophoblast, cytotrophoblast, and extra-embryonic mesoderm cells. Together, these components proliferate and form the chorionic villi. As development progresses, this membrane functionally integrates with the maternal endometrium to establish the placental interface that is vital for the growing embryo.