Fig. 6

Development of the portal vein. A Paired vitelline veins are connected by three anastomoses. The duodenum lies ventral to the intermediate anastomosis. The dorsal pancreatic bud arises ventrally to the left vitelline vein, and the ventral pancreatic bud arises contralateral and slightly caudal to the dorsal pancreatic bud. B Normal development of portal vein and pancreas. The lower part of the right vitelline vein and the upper part of the left vitelline vein disappear, and the intermediate anastomosis on the dorsal side of the duodenum forms the portal vein main trunk. As the duodenum rotates, the ventral pancreatic bud fuses behind the dorsal pancreatic bud. C Development of the prepancreatic postduodenal portal vein. The dorsal pancreatic bud arises on the dorsal side of the left vitelline vein, or arises caudal to the intermediate anastomosis, which results in the portal vein posterior to the duodenum but anterior to the pancreas. SV sinus venosus, d dorsal pancreatic bud, v ventral pancreatic bud, VV vitelline vein, UV umbilical vein, PV portal vein, PPPV prepancreatic postduodenal portal vein