230 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



sinus venosus (Fig. 187). The liver is developed between and 

 around the vitelline and umbilical veins, near their termination 

 in the sinus venosus. The veins are broken up and a fine 

 intra-hepatic venous network takes their place. Thus it comes 

 about that the vitelline veins are transformed into the veins of 

 the portal and hepatic circulation. All the foetal and umbilical 

 blood is at first poured through the liver. 



azy. vein 



rt. umb. 



rt. i//f.__^ 



inf. uen. cau. 



ductus uen. — ■ 



in transv. fis] 

 of liver J 



portal vein 



;\ /Lvein of Marshall 



stomach 



remnants of left umb. 



rt. uit. vein -■ 



left uit. vein 

 part disappears 

 left umb. vein 



rt. umb. vein (disappears) 

 duodeno-jej. pleure 



left vit. vein. 



left vit vein 



sup. mesent. vein 



Fig. 18S. — Diagram showing the Formation of the Ductus Venosus, and the fate of 

 the Umbilical and Vitelline veins. The arrows show the parts of the Vitelline 

 Veins which become the Portal Vein. 



The Ductus Venosus is a new channel formed between the 

 uppermost of the anastomoses between the right and left vitelline 

 veins and the sinus venosus whereby the greater part of the 

 umbilical blood is short-circuited to the heart without passing 

 through the liver. It appears after the liver bud has broken up 

 the vitelline venous trunks (Fig. 188). After birth, when a 

 short circuit is no longer required between the foetal circulation 

 and heart, it becomes reduced to a fibrous cord. It occupies the 

 posterior part of the longitudinal fissure of the liver and lies 

 within the hepatic attachment of the gastro-hepatic omentum. 



