DEVELOPMENT OF THE HEPATIC CIRCULATION. 677 



Fig. 265. 



as follows : A certain quantity of venous blood still enters through 

 the portal vein ( i ), and circulates in a part of the capillary system 

 of the right lobe. The umbilical vein (a), bringing a much larger 

 quantity of blood, enters the liver also, a little to the left, and the 

 blood which it contains divides into three principal streams. One 

 of them passes through the left branch (3) into the capillaries of the 

 left lobe ; another turns off through the right branch (4), and, join- 

 ing the blood of the portal vein, circulates through the capillaries 

 of the right lobe ; while the third passes directly onward through 

 the venous duct (5), and reaches the hepatic vein without having 

 passed through any part of the capillary plexus. 



This condition of the hepatic circulation continues until birth. 

 At that time, two important changes take place. First, the pla- 

 cental circulation is altogether cut off; and secondly, a much larger 

 quantity of blood than before begins 

 to circulate through the lungs and 

 the intestine. The superabundance 

 of blood, previously coming from the 

 placenta, is now diverted into the 

 lungs ; while the intestinal canal, en- 

 tering upon the active performance of 

 its functions, becomes the sole source 

 of supply for the hepatic venous 

 blood. The following changes, there- 

 fore, take place at birth in the ves- 

 sels of the liver. (Fig. 265.) First, 

 the umbilical vein shrivels and be- 

 comes converted into a solid rounded 

 cord (i). This cord may be seen, in 

 the adult condition, running from the 

 internal surface of the abdominal 

 walls, at the umbilicus, to the longi- 

 tudinal fissure of the liver. It is then 

 known under the name of the round 



ligament. Secondly, the ductus venosus also becomes obliterated, 

 and converted into a fibrous cord. Thirdly, the blood entering the 

 liver by the portal vein (i), passes off by its right branch, as before, 

 to the right lobe. But in the branch (4), the course of the blood is 

 reversed. This was formerly the right branch of the umbilical 

 vein, its blood passing in a direction from left to right. It now 

 becomes the left branch of the portal vein ; and its blood passes 



Adult form of HEPATIC CmcrLA- 

 TIOS. 1. Portal vein. 2. Obliterated 

 umbilical vein, forming the round liga- 

 ment; the continuation of the dotted 

 lines through the liver shows the situa- 

 tion of the obliterated ductus venosus. 

 3. Hepatic vein. 4. Left branch of portal 

 vein. 



