38 CHARLES F. W. McCLURE AND GEORGE S. HUNTINGTON 



('65), Harrison ('39), McWhinnie ('40), Oberndorfer ('03), 

 Paterson ('01), Quain ('44), Waring ('94), and Zum- 

 stein ('95). 



Type C and Type BC are the variants of the vena cava 

 inferior which occur most frequently in adult man. 



14. Persistence of left supracardinal and left posterior 



cardinal veins. Periureteric venous ring present 



on left side, through which ureter passes 



Type CD (C and D in fig. 1) 



No instance has thus far been described, either in the adult 

 cat or in man, in which the left supracardinal and the left 

 posterior cardinal veins have alone persisted to form a 

 periureteric venous ring on the left side. Type CD is a 

 mirror picture of Type AB (fig. 9), with the venous ring on 

 the left instead of the right side. Two cases have been 

 described in mammals in which a periureteric venous ring 

 was present on the left side but in combination, however, 

 either with a supracardinal or with a supracardinal and a pos- 

 terior cardinal on the right side. The two cases referred to 

 were described, respectively, by Hochstetter ('93) in Erina- 

 ceus europaeus (Type ABCD) and by Metcalf ('18) in the 

 cat (Type BCD). (See figure 17 of the present monograph, 

 in which Metcalf 's figure has been reproduced.) While the 

 presence of a periureteric venous ring on the left side is of 

 rare occurrence in the adult cat, it is always present in the 

 embryo (fig. 45), and is therefore potential for the adult. 



15. Persistence of left posterior cardinal vein 



Type D (D in fig. 1). Figure 53, cat (Darraeh Series) 



Type D is a mirror picture of Type A, in which the cava is 

 formed by the right posterior cardinal vein. Type D repre- 

 sents a case in which, caudal to the renal level, the cava is 

 single, and lies on the left side of the abdominal aorta, with 

 the left ureter passing between the aorta and the caval vein 

 (fig. 53). The position which the left ureter bears to the cava 

 indicates that the latter was derived from the left posterior 

 cardinal vein. 



