DEVELOPMENT OF THE VASCULAR SYSTEM. 



801 



HEPATIC CIRCULATION during the 

 latter part of foetal life. 1. Portal vein. 

 2. Umbilical vein. 3 Left branch of um- 

 bilical vein. 4. Eight branch of umbili- 

 cal vein. 5. Ductus venosus. 6. Hepatic 

 vein. 



Fig. 308. 



them passes through the left branch Fig. 307. 



(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 directly 

 onward through the ductus venosus 

 (5) and reaches the hepatic vein with- 

 out having passed through any part 

 of the capillary plexus. 

 ' This condition of the hepatic cir- 

 culation continues until birth. At 

 that time, two important changes 

 take place. First, the placental cir- 

 culation is cut off; and secondly, a 

 much larger quantity of blood than 

 before begins to circulate through the 

 vessels of the lungs and the intestine. 



The superabundance of blood, previously coming from the placenta, is 

 now diverted to the lungs ; while the intestinal canal becomes the sole 

 source of supply for the hepatic venous 

 blood. The following changes, there- 

 fore, take place at birth in the vessels 

 of the liver. (Fig. 308.) First, the um- 

 bilical vein shrivels and becomes con- 

 verted into a solid cord ( 2 ). This cord 

 may be seen, in the adult condition, 

 running from the internal surface of the 

 abdominal walls, at the umbilicus, to 

 the longitudinal fissure of the liver. It 

 is then known under the name of the 

 round ligament. Secondly, the ductus 

 venosus also becomes obliterated. 

 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 left branch (* ) the course of 

 the blood is reversed. This was for- 

 merly 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 from right to left, to be distributed to the capillary vessels 

 of the left lobe. 



According to Guy, the umbilical vein is completely closed at the end 

 of the fifth dav after birth. 



Adult form of HEPATIC CIRCU- 

 LATION. 1. Portal vein. 2. Oblite- 

 rated umbilical vein, forming the round 

 ligament ; the continuation of the dot- 

 ted lines through the liver shows the 

 situation of the obliterated ductus 

 venosus. 3. Hepatic vein. 4. Left 

 branch of portal vein. 



