A morphological study of the development of the human liver. II. Establishment of liver parenchyma, extrahepatic ducts and associated venous channels

The establishment of liver parenchyma, extrahepatic ducts and associated venous channels were examined in serial sections of 100 human embryos representative of Horizons XI through XVII. The liver parenchyma first begins to develop from the cephalic end of the hepatic diverticulum in embryos between the 20‐ and 25‐somite stage. The parenchyma develops as cords from the walls of the diverticulum which anastomose around isolated endothelium‐lined spaces (blood islands) in the septum transversum. As growth and anastomoses of the parenchymal cords continue, the isolated endothelium‐lined spaces form an interconnecting capillary bed which interdigitates with the developing parenchymal cords. The larger omphalomesenteric veins develop simultaneously with the parenchyma and are continuous with the smaller venous channels which interdigitate with the parenchymal cords. These larger developing veins become surrounded by the developing parenchymal cords. As the parenchymal cords branch from the cephalic end of the diverticulum, that portion of the diverticulum becomes reduced to a small tubular structure, the common hepatic duct, which is always continuous with the parenchyma. As the cephalic portion of the original diverticulum is reduced in size, there is a localized outgrowth from the ventral wall of the caudal end of the original diverticulum. This localized outgrowth becomes the cystic duct and gallbladder. The remainder of the caudal segment of the diverticulum elongates to become the common bile duct. The ventral pancreas develops as a localized outgrowth from the dorsal wall of the common bile duct.