THE MAMMALIAN VENA C'AYA POSTERIOR 27 



('93), and later by Gage ('98), and McClnre ('00). We know 

 of but one instance on record in which it has been found in 

 man. This is a case observed in an acardiac foetus by Glad- 

 stone (fig. 8, '12) and illustrated here by figure 25. 



9. Persistence of right supracardinal vein. Normal vena cava 

 posterior (inferior) in the cat and hi man 



Type B (B in fig. 1). Figures 26, cat (Darrach Series); 27, man (Flourens, 

 '36); 28, man (Huntington Collection); 29, man (Huntington Collection); 

 30, man (Vesalius, 1543); 31, man (Froriep, '95), and 32, man (Huntington 

 Collection) 



In both cat and man the type of vena cava posterior rep 

 resented by Type B is one in which, caudal to the renal veins, 

 the cava is single and lies on the right side of the abdominal 

 aorta. The right sex vein (V. spermatica interna) opens into 

 the cava, slightly caudal to the level of the right renal vein, 

 and the left sex vein into the left renal vein. On leaving the 

 kidney, the right ureter extends directly to the bladder with- 

 out passing between the aorta and the caval vein. Type B, in 

 both cat and man, is due to the persistence in the adult of the 

 right lumbar supracardinal vein (Sprc. B, fig. 1). 



The sex veins in the cat are formed by the posterior cardi- 

 nal and the subcardinal veins. An elongation of the right side 

 of the renal collar (Siibc.Sprc.Anast.Dext., figs. 1 and 4), to 

 the caudal border of which the posterior cardinal with its 

 sex-vein tributary is attached, accounts for the entrance of 

 the right sex vein into the cava, caudal to the level of the 

 right renal vein. In the cat, after the loss of the left side 

 of the renal collar (Subc.Sprc.Anast., figs. 1 and 5), the left 

 renal vein drains into the cava by the subcardino-posterior 

 cardinal anastomosis (Subc.Pc.Anast.}, to which the posterior 

 cardinal with its sex-vein tributary is attached. In this man- 

 ner may be explained the difference, which, in the cat, exists 

 on opposite sides in the relations which the sex veins bear i<> 

 the cava and to the left renal vein. 



McClure and Butler ('25) have recently shown that in man 

 the sex veins are derived exclusively from the subcardinal 

 veins and that each subcardinal, near the intennbcardinal 



