Early placentation in the dusky leaf monkey (Presbytis obscura).

Implantation in the dusky leaf monkey, Presbytis obscura, is superficial; the placenta is of the double discoid villous haemochorial type. Immediately prior to implantation the thick endometrium contains highly active uterine glands. There is an early uterine epithelial proliferation at the implantation site but no stromal decidual response. The fetal villi are evenly spread over that part of the chorion in contact with the endometrium and consist of a mesenchymal core covered by an inner layer of cytotrophoblast and an outer layer of syncytiotrophoblast. The endothelial cells of the maternal vessels undergo swelling before disruption of the vessel walls and the establishment of a circulation through the intervillous spaces.