Figure 2. Drawings illustrate the embryologic development of the hepatic venous system. Initially, the vitelline veins (1) enter the embryo with the yolk stalk and anastomose with each other around the duodenum (2) before passing through the septum transversum (3) on their way to the sinus venosum (4). The umbilical veins (5) course on either side of the septum transversum and come into contact with the sinusoids. The proximal part of the left vitelline vein involutes, and all the blood coming from the left side of the liver is redistributed to the right vitelline vein. The entire right umbilical vein, part of the left umbilical vein, and the left sinus venosus also degenerate. In the final configuration of the fetal hepatic venous system, the left umbilical vein brings all the oxygenated blood to the embryo. The ductus venosus (6) connects the umbilical vein with the inferior vena cava (IVC) (7). The portal venous system (8) originates from a selective involution of the anastomotic network around the duodenum.