CONTENTS 



I. Foreword 5 



II. The normal and the atypical vena cava posterior (inferior) 7 



III. The supracardinal system of veins 7 



IV. A reconstruction of the axial veins in the lumbar region of a 16-mrn. 



cat embryo 8 



V. The composite ontogenetic venous plan of the cat 12 



VI. The atypical forms of the vena cava posterior in adult man and the 

 cat, interpreted on the basis of their development from a com- 

 mon ground plan, by selection of potentially available pathways 

 in the embryo 17 



1. Persistence of right posterior cardinal vein (Type A) 18 



2. Persistence of right posterior cardinal and right supracardinal 



veins. Eight periureteric venous ring present, through whifh 

 ureter passes (Type AB) 19 



3. Persistence of right posterior cardinal, right supracardinal, and 



left supracardinal veins. Bight periureterie venous ring 

 present, through which ureter passes (Type ABC) 21 



4. Persistence of right posterior cardinal, right supracardinal, left 



supracardinal, and left posterior cardinal veins. Right and 

 left periureteric venous rings present, through which ureters 

 pass (Type ABCD) 21 



5. Persistence of right posterior cardinal, right supracardinal, and 



left posterior cardinal veins. Right periureteric venous ring 

 present, through which ureter passes (Type ABD) 22 



6. Persistence of right posterior cardinal and left supracardinal 



veins (Type AC) 23 



7. Persistence of right posterior cardinal, left supracardinal, and 



left posterior cardinal veins. Left periureteric venous ring 

 present, through which ureter passes (Type ACD) 24 



8. Persistence of right and left posterior cardinal veins (Type AD) -' 



9. Persistence of right supracardinal win. Normal vena eava 



posterior (inferior) in the cat and in man (Type B) 27 



10. Persistence of right and left supracardinal veins (Type BC) .. 31 



11. Persistence of right and left supracardinal, and left posterior 



cardinal veins. Periureteric venous ring present on left side, 

 through which ureter passes (Type BCD) 35 



12. Persistence of right supracardinal and left posterior cardinal 



veins (Type BD) 



13. Persistence of left supracardinal vein (Type C) 37 



14. Persistence of left supracardinal and left posterior cardinal 



veins. Periureteric venous ring present on left side, through 

 which ureter passes (Type CD) 



15. Persistence of left posterior cardinal vein (Type D) 38 



3 



