Histological Classification of Placenta || Epithelio-chorial placenta

 Epithelio-chorial placenta

        The first type that is encountered with least modifications, is the epithelio-chorial placenta. This type of placenta is met with some ungulates and lemur. Here the allantois and chorion fuse together and are supplied jointly with allantoic vessels. 

        The allantoic-chorion membrane comes in contact with uterine lining and the chorionic villi fit into the pits in the uterine mucosa. Here there is simple application of chorion against the epithelium of uterus and hence the relationship is called the epithelio-chorial. The space between the chorion and uterine lining are filled with a fluid consisting of secretions and transudates. This fluid is called the "uterine milk." The nutrition and oxygen pass from maternal blood through this epithelio-choridal tissue Placentation in Mammals and then is fed to allantoic vessels. The waste products produced due to foetal metabolic activities are passed out through the same passage but in a reverse direction. 

        Thus, the allantois here is performing the function of an organ of respiration, excretion and nutrition. This type of placenta is also met with some reptiles and birds.