chorion One of the two membranes that surrounds the embryo. The chorion lies outside the amnion and is formed from trophoblast lined with mesoderm and becomes closely associated with the allantois. The blood vessels (supplied by the allantois) are concentrated in the region of the chorion that is attached to the wall of the uterus and develops into the placenta. Chorionic tissue may be removed for prenatal or antenatal diagnosis. See chorionic villus sampling. Related categories • ANATOMY AND PHYSIOLOGY • DEVELOPMENTAL BIOLOGY Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) |