Umbilical part

The left branch of portal vein consists of two successive segments named according to their orientation in the human liver: the transverse part (Pars transversa) and the umbilical part (Pars umbilicalis). The latter, which curves toward the fissure of the round ligament, is so named because in the fetus it directly prolonged the umbilical vein (V. umbilicalis), whose extrahepatic portion, obliterated after birth, becomes the round ligament of the liver (Lig. teres hepatis). The boundary between the two parts of the left branch is marked by the fibrous remnant of the ductus venosus (Ductus venosus), which in the fetus connected the umbilical vein to the caudal vena cava. The distinction between the two parts is difficult in species where this fibrous remnant is itself barely distinguishable (e.g., Equidae).