[Morphology and distribution of venous openings in the human placenta]

A human in situ placenta of the fourth lunar month was totally serial sectioned and light microscopically examined with following results: 1. 252 venous openings had been found. 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 is a large part of the placenta with most of veins, the so called venous ring, lying between the central part and the marginal lake. b) in the central parts are remarkably less, venous openings as in the venous ring. c) the vessels lie together in groups. 4. only few veins have direct connection with the marginal lake, they have a regulation basin function to equalize the different intervillous blood pressure. 5. there is no topographic relationship between venous openings and plaental septa; although sometimes veins could be found in the near or at the vase of placental septa. 6. the venous endings possess according to their localization different structures: a) in the central parts often narrow, chimney- like endings connected with a venous lake, b) in the venous ring many uncharacteristic forms: broad shaft- like endings, hook- like endings and also multiple openings of one single vein. c) near the marginal lake the vessels run stretched out parallel to the basal plate, partly terraced one upon another. 7. valves do not exist.