While at first the ductus venosus communicates throughout its entire length with the meshwork of the hepatic capillary system, a separation into two segments, _i. e._, ductus venosus proper and intrahepatic segment of umbilical vein, is established after the free communication with the left umbilical vein takes place. This condition is exhibited in Fig. 258, which represents the corroded venous system of the foetal liver, and in Fig. 259, showing an injected liver in the foetus at term. [Illustration: FIG. 258.--Corrosion preparation of venous system of human liver in foetus at term. (Columbia University Museum, No. 1834.)] [Illustration: FIG. 259.--Injected and hardened human liver from foetus at term. (Columbia University Museum, No. 1853.)] It will be observed that the umbilical vein on entering the liver gives off a large branch to the left lobe, and a smaller branch on the right side to the quadrate lobe, which act as the main venae advehentes of these portions of the liver. Arrived at the transverse fissure the umbilical vein divides into three branches, at right angles to each other. The left branch enters the left lobe, the right branch becomes directly continuous with the left main division of the portal vein, while the central branch, continuing the direction of the umbilical vein, passes dorsad, as the ductus venosus proper, to join the left hepatic vein close to its entrance into the postcava. =5. Changes Consequent upon the Establishment of Pulmonary Respiration.=--After birth the umbilical vein and its continuation, the ductus venosus, become obliterated, the former constituting the round ligament of the liver, the latter the ligament of the ductus venosus, both structures imbedded in corresponding portions of the sagittal fissure on the caudal and dorsal surfaces of the adult liver (Figs. 284 and 286). The lateral branches of the umbilical vein, however, in its course from the ventral margin of the liver to the transverse fissure (Fig. 258), remain pervious and are transferred to the portal circulation. [Illustration: FIG. 260.--Diagram of intrahepatic foetal venous circulation.] [Illustration: FIG. 261.--Diagram illustrating the changes in the intrahepatic venous circulation resulting from the cessation of the placental circulation at birth.]