[Distribution of the chorionic vessels of the human placenta and their arteriovenous crossings (author's transl)].

We examined 100 selected placentas concerning architecture and distribution of the vessels of the chorionic plate. The eccentric insertion of the umbilical cord as well as the mixed type of distribution of the chorial arteries and equal areas of arterial blood supply were found to be most frequent. In no case the anastomosis of Hyrtl was absent. A marginal and a very eccentric cord were more frequent in combination with a mixed and magistral type of distribution of the vessels that the lesser eccentric and the central type of insertion. There was no significant correlation between insertion of the cord and the infants' birth weight. Arteries pass over the veins when they cross. Serial sections of 15 crossing vessels have been examined, one specimen was reconstructed graphically. When crossed by major arteries the veins bypass below whereas small arterial branches override larger veins not affecting their course. The cross-like vessels are wrapped up in connective tissue and anchored to the chorion plate. There are equivalents in the morphology of the vessels of the chorion and the retina. Both vessel systems are embedded in hollow bodies exposed to an inner pressure, however, sharing a common media, the crossing artery and vein of the retina represent a more intense anatomical unity. The connective mesenchymal frame of the crossing vessels of the choroin plate, the thickened arterial wall-segments and the venous wall-sectors let functional valves suspect as is known from other areas of blood supply.