Chorion bald - see Chorion smooth.
Smooth chorion (lat. chorion laeve) is one of the types of placenta in mammals. It is characterized by the fact that the villous chorion (a structure formed by trophoblast cells) fits tightly to the wall of the uterus without growing into its tissue.
Chorion smooth is found in horses, pigs, cetaceans and some other species. It provides a diffuse type of uteroplacental circulation, in which the mother’s blood washes the villous chorion, but does not directly contact the fetal blood. Nutrients and oxygen penetrate through the walls of the villi to the blood vessels of the fetus.