THE MAMMALIAN VENA CAVA POSTERIOR 15 



These Types are as follows (see A, B, C, and D, in fig. 1) : 



1. Type A, persistence of right posterior cardinal vein (A). 



2. Type AB, persistence of right posterior cardinal (A) 

 and right supracardinal (B) veins. Bight periureteric ve- 

 nous ring present, through which ureter passes. 



3. Type ABC, persistence of right posterior cardinal (A), 

 right supracardinal (B), and left supracardinal (C) veins. 

 Right periureteric venous ring present, through which ureter 

 passes. 



4. Type ABCD, persistence of right posterior cardinal (A), 

 right supracardinal (#), left supracardinal (C), and left pos- 

 terior cardinal veins (D). Right and left periureteric venous 

 rings present, through which ureters pass. 



5. Type ABD, persistence of right posterior cardinal (A), 

 right supracardinal (B), and left posterior cardinal veins 

 (D). Right periureteric venous ring present, through which 

 ureter passes. 



6. Type AC, persistence of right posterior cardinal (.4), 

 and left supracardinal veins (C). 



7. Type A CD, .persistence of right posterior cardinal (J.), 

 left supracardinal (C), and left posterior cardinal veins (D). 

 Left periureteric venous ring present, through which ureter 

 passes. 



8. Type AD, persistence of right (A) and left (D) posterior 

 cardinal veins. 



9. Type B, persistence of right supracardinal vein (B) to 

 form the lumbar division of the posterior vena cava. Normal 

 cava. 



10. Type BC, persistence of right (B) and left (C) supra 

 cardinal veins. 



11. Type BCD, persistence of right (B) and left supracar- 

 dinal (C), and left posterior cardinal veins (Z>). Left peri- 

 ureteric venous ring present, through which ureter passes. 



12. Type BD, persistence of right supracardinal (B) and 

 left posterior cardinal veins (D). 



13. Type C, persistence of left supracardinal vein (C). 



