30 CHARLES F. W. McCLTJRE AND GEORGE S. HUNTINGTON 



the case of the variant shown in figure 31, the cranial half 

 of the left lumbar supracardinal forms the major portion of 

 the left renal vein, which, caudal to the renal level and dorsal 

 to the aorta, joins the caval vein. In this connection it is 

 interesting to examine the conditions shown in figure 35. In 

 this case, if the right renal vein were to give up its connec- 

 tion with the cava at the renal level, the right supracardinal, 

 into which the right sex vein opens, would then function as a 

 renal vein and, through its intersupracardinal anastomosis, 

 would have the same relations to the sex vein, the aorta, and 

 the vena cava, as does the left renal vein in figure 31. An 

 essentially similar accessory left renal vein opening into the 

 caval vein has been described by Watt ( '20). 



Another example of an atypical left renal vein is shown in 

 figure 32. In this case, in addition to a right and a left renal 

 vein that are typical in all respects in their relations to the 

 cava and the sex vein, there is present an accessory left renal 

 vein. On emerging from the left kidney, this accessory renal 

 vein passes caudad and mesad to open into the cava, ventral 

 to the aorta, at the point where the cava is joined by the 

 common iliac veins. Since a typical renal vein is present on 

 the left side, it is evident that this accessory renal vein can- 

 not have been derived from the renal veins, which in the 

 embryo open into the renal collar (McClure and Butler, '25). 

 The only available embryonic pathways which could be re- 

 tained in the formation of this accessory renal vein are the 

 cardinal collateral (C.C., figs. 1, 4, and 5) and the left sub- 

 cardinal veins (Subc., fig. 1). The manner in which its con- 

 nection with the kidney came about is still problematical, 

 although no doubt can exist ab6ut its cardinal collateral 

 origin (C.C., fig. 1) in the region where, ventral to the aorta, 

 the accessory renal vein opens into the caval vein. 



