Stage III parturition, fetal membranes at vulva, mare
Courtesy of Dr. Patricia Sertich.
Most of the time (~80%), the umbilical cord causes inversion of the chorioallantois so that the shiny gray surface of the allantois is on the outside of the expelled membranes. The amnion is seen between the allantois and the mare's tail. It is also normal for the red velvety chorion to be on the outside of the expelled membranes.