The parabiliary venous system.

The parabiliary venous system originates from the pancreatico-duodenal and pyloro-duodenal veins, runs along the common bile-duct and the hepatic artery, and divides in the liver hilum into a venous network within the hilar plate. Embryologically, this system, apparently independent of the portal vein, develops together with the bile-ducts and the hepatic artery: these three structures are within the substance of the vasculo-biliary sheaths, and the whole complex invades the liver well after the distribution of the portal vein has been established. It should be pointed out that segments I and IV also appear rather late. Seventy-four specimens with injection of the system have been studied. The hilar plexus sends branches to the veins of the segments adjacent to the hilum. Some vessels directly supply the inferior surface of the quadrate lobe or the caudate lobe, or the left lobe. In 46.50% of specimens, part of the cystic veins are anastomosed with the parabiliary system.