THE integrity of the conceptus in man must depend directly upon the provision and maintenance of an adequate supply of maternal blood to the intervillous space. Until we understand how this supply is provided and maintained throughout all the changes in maternal haemodynamics accompanying uterine, placental and foetal growth, we are likely to comprehend little of the physiological interrelation between mother and foetus, and even less of placental pathology. To provide the necessary blood supply for the growing conceptus the maternal blood vessels have to undergo extensive adaptations and structural alterations. In any other situation these vessel changes would be regarded as pathological, but, in spite of their obvious importance, surprisingly little attention has been devoted to the arteries feeding the intervillous space and the veins draining blood from it.

The first histological studies of these vessels in late pregnancy appear to have been carried out by Friedlander (1870). He described large basophilic cells with single prominent nuclei in the wall of the arteries leading into the intervillous space and suggested that they were trophoblastic cells with power to invade and perforate the arterial wall. Schickele (1904) made essentially similar observations, and Frank1 and Stolper (1910) described thesevessels in pregnancy as being like hyaline tubes with large cells in their walls. Schwarz and McNalley (1923) considered that the entire wall of the vessel showed a diffuse thickening, and Williams (1931) described the appearance of fibrinoid and hyaline structures of bizarre outline in collapsed vessels. Over the last 20 yr there has been a revival of interest in the histological appearances of these vessels, but most authors (Hertig, 1945; Zeek and Assali, 1950; Dixon and Robertson, 1958, 1961; Marais, 1962a-f; Pinkerton, 1963; Jonas and Rewell, 1963) have concentrated their attention on these vessels in abnormal pregnancy.