DEVELOPMENT OF THE CIRCULATORY SYSTEM. 



227 



From the right cardinal vein are formed (1) the vena azygos 

 major ; (2) the post-renal part of the inferior vena cava (Fig. 186). 



The part above the entrance of the right renal becomes the 

 vena azygos major ; the part below, the inferior vena cava. 

 Hence it is that the origin of the vena azygos can commonly be 

 traced to the renal vein. The ascending lumbar vein, which also 

 ends in the vena azygos major, is, as already mentioned, a new 

 anastomotic channel. 



From the left cardinal arise (Fig. 186) — (1) Part of the left 

 superior intercostal vein ; (2) Left superior azygos vein ; (3) Left 



right duct of Cuuier 



sinus uenosus 



right jug- 



right card, veini- 



vena azyg. 



'. majr^. 



kidney— L 

 sperm, vein^ff^ 



inf. uen. cava, 

 (post-renal) 



leftjug. 



left card, vein 

 t~left sup. intercost 



left sup.uena azyg. 





± if 



right ext. iliac Sa /T^ f^^ '"*' " 



II I \U/*"~ 



left com. iliac 



4— kidney 



sperm, vein 



; 4— disappears 

 left card. 



iliac 

 int. iliac 



Fig. 186.-The Remnants of the Posterior Cardinal Veins in the Adult. The new 

 channels are shaded. (After Hoohstetter.) 



inferior azygos, which commences in the left renal vein, and also 

 receives the left ascending lumbar. The post-renal part of the 

 left cardinal disappears in higher mammals; occasionally it persists 

 in man and very frequently in the rabbit. 



