OF CIRCULATION. 



193 



niesaraic which passed around the liver degenerates, and the 

 anterior portions of these veins become converted into the he- 

 patic veins, conveying blood from the liver to the sinus venosus. 

 In this process that portion of the omphalomesaraic vein between 

 the liver and the origin of the vitelline vein becomes twisted, so 

 as to surround the intestine in a spiral manner; and this portion 



AA 



SX. 



FIG. 204. Scheme of the circulation in a chick of the third day from below, 

 after Balfour from Wiedersheim. A A, aortic arches; Ao, dorsal aorta'; DC, ductus 

 Cuvierii ; //, heart; Lof, left omphalomesaraic vein; LofA, left omphalomesarnic 

 artery; A'O/, 7\OfA, right omphalomesaraic vein and artery; SCal r , anterior 

 cardinal vein; ST, sinus venosus; ST, sinus terminalis; VC<i, posterior cardinal 



persists throughout life as the portal vein which brings blood 

 from the intestine to the liver, while that part of the caudal 

 vein which lies in the intestinal region develops into the sub- 

 intestinal vein of the adult. The fate of the posterior part of 

 the caudal vein will be given below. 



The posterior cardinals at first extend back to the anterior 



