Two primordia contribute to the development of the liver (Figure 8.1). The parenchyma is entirely derived from the hepatic diverticulum while the stoma is derived from the septum transversum. The hepatic diverticulum appears as an outgrowth of the endodermal epithelium at the distal end of the foregut (future duodenum) and days 29 (stage 11).1 This outgrowth penetrates the septum transversum, that is, the mesodermal plate that separates the embryonic thoracic and abdominal cavities (Figure 8.1 A). The endodermal cells in the cranial part of the diverticulum that penetrate the septum transversum differentiate into hepatocytes and epithelial cells of the bile ducts. The mesenchymal cells of the septum transversum form the connective tissue elements of the hepatic stroma and capsule. The caudal part of the hepatic diverticulum, the portion that does not invade the septum transversum, forms the gallbladder, cystic duct, common bile duct, and ventral pancreatic anlage. As the liver rapidly grows during the weeks following the initial budding of the hepatic diverticulum, it separates from the residual mesenchyme of the septum transversum, which becomes the diaphragm. The portal vein is formed by week 7 of gestation as the paired vitelline veins unite and enter the developing porta hepatis. The primitive hepatic sinusoids are formed as the capillary plexus derived from the vitelline veins penetrate the developing hepatic sheets within the septum transversum. The vitelline veins emerge from the septum transversum and drain into the sinus venosus of the cardiac primordium. The left-sided vein degenerates, while the right vitelline vein forms the inferior vena cava, which thus receives the hepatic venous outflow.