THE THORAX 



1013 



the subcardina vein with the posterior cardinal vein, opposite the future 

 right renal vein. 



The right subcardinal vein becomes connected superiorly, behind the liver 

 and within the caval mesentery, with hepatic veins by means of a fusion 

 betsveen hepatic and subcardinal sinusoids. In this manner a venous channel 

 is formed, which leads to the common hepatic vein and thence to the heart. 

 The right subcardinal and posterior cardinal veins being in free commimica- 

 tion with each other, much of the venous blood from the caudal pjirt of the 

 body can flow through the new channel, formed in the caval mesentery by 

 the fusion of the hepatic and subcardinal sinusoids, into the common hepatic 



Posterior Cardinal Vein 



Fig. 418. — The Development of the Vena Cava Inferior (Early Stages). 

 Cardinal and Subcardinal Veins, etc. 



(Frederick T. Lewis, in the American Journal of Anatomy.) 



vein, and thence to the heart. The blood of the posterior cardinal veins can 



therefore now reach the heart through two channels — namely: (i) the upper 

 part of the right subcardinal vein, the new path within the caval mesentery, 

 and the common hepatic vein; and (2) the duct of Cuv-ier. The first channel 

 is taken by the blood of the lower parts of the posterior cardinal veins, and 

 the second channel by the blood from the upper parts of the posterior cardinal 

 veins, above the Wolffian bodies. 



The subcardinal and posterior cardinal veins of each side are divided into 

 two parts — lower and upper — by the great transverse pre-aortic anastomotic 

 vessel. The lower parts of the two subcardinal veins atrophy. The upper 

 part of the right subcardinal vein persists, and forms a portion of the 



