[Morphologic studies on the venous blood drainage of the human placenta]

A human in situ placenta of the eleventh week of pregnancy was totally serial sectioned and light microscopically examinated with following results: 1. 208 venous openings were counted 2. Venous drainage takes place over the whole basal plate 3. the venous openings are scattered in different regions a) mainly responsible for the venous drainage are the border parts of the placenta between central parts and the marginal lake b) the openings lie together in cricoid groups. This pleads for the existence of circulation units 4. there is no relationship perceptible between venous openings and placental septa 5. venous valves and arteriovenous anastomoses do not exist.