The chorion lies closest to the placenta. The chorionic sac encompasses the fetus and the amnion and is covered with chorionic villi until the 8th week. After the 8th week, these villi are ...

In its early life, the placenta is called a chorion because it is formed from the chorionic villi - finger-like growths which develop on the fertilised egg to help it implant in the wall of the ...

The outer membrane (chorion) and trophoblast layer of the placenta are derived from the trophoectoderm of the blastocyst cells. Other extra-embryonic tissues, including the amnion (inner membrane ...