696 



REPRODUCTION. 



placental blood reaches the heart without passing through the hepatic 

 capillaries. This canal is the Ductus venosus. 



The ductus venosus is formed by a dilatation of one of the hepatic 

 capillaries (Fig. 244), which is thus converted into a wide branch of 

 communication between the umbilical vein below and the hepatic vein 

 above. The circulation in the liver, at this period, is as follows : A 

 certain quantity of venous blood still enters through the portal vein (,), 

 and circulates in a part of the capillary system of the right lobe. The 

 umbilical vein ( 2 ) enters the liver a little to the left, bringing a larger 

 quantity of blood, which divides into three principal streams. One of 



FIG. 244. 



FIG. 245. 



HEPATIC CIRCULATION during the latter 

 part of foetal life. 1. Portal vein. 2. Um- 

 bilical vein. 3. Left branch of umbil- 

 ical vein. 4. Eight branch of umbilical 

 vein. 5. Ductus venosus. 6. Hepatic 

 vein. 



ADULT FORM OF HEPATIC ( 'i 



1. Portal vein. 2. Obliterated umbilical 

 vein, forming the round ligament; tlip 

 continuation of the dotted lines through 

 the liver shows the situation of the ob- 

 literated ductus venosus. 3. Hepatic vein. 

 4. Left branch of portal vein. 



them passes through the left branch of the umbilical vein ( 3 ) into the 

 capillaries of the left lobe ; another turns off through the right branch 

 ( 4 ), and, joining the blood of the portal vein, circulates through the 

 capillaries of the right lobe ; while the third passes through the ductus 

 venosus ( 5 ) to the hepatic vein without traversing any part of the 

 capillary plexus. 



This form of the hepatic circulation continues until birth. At that 

 time, two important changes take place. First, the placental circula- 

 tion is cut off; and secondly, a much larger quantity of blood than 

 before is supplied to the lungs and the intestine. The superabundant 

 blood, previously circulating in the placenta, is now diverted to the 

 lungs ; while the intestinal canal becomes the only source of venous 

 supply for the hepatic blood. The following changes, therefore, take 

 place in the liver (Fig. 245). First, the umbilical vein shrivels and 

 becomes impervious. It remains in this condition, in the adult, as the 

 round ligament ( 2 ), extending from the inner surface of the abdominal 

 walls, at the umbilicus, to the longitudinal fissure of the liver. Secondly, 



