The origin of placental septa and the orifices of spiral arteries have been the subject of great controversy. The anatomy of the venous drainage has also been the subject of much discussion. The intrusive cells in the lumen as described by C. Friedlander were intensively studied by J. D. Boyd and W. J. Hamilton using their large collection of uterine specimens with the placenta in situ. The delivered placenta and fetal membranes were for many years the commonest method of obtaining material for the study of spiral artery pathology, and there were large discrepancies between the findings in this material. The method of placental bed biopsy produced useful material, but nevertheless was criticized by Hamilton and Boyd. The spiral artery anatomy as well as the vascular pathology were only revealed after studying uteri with in situ placentae pregnancy that compromise both maternal and fetal health.