THE MAMMALIAN VENA CAVA POSTERIOR 21 



3. Persistence of right posterior cardinal, r if/ fit supracardinal, 



and left supracardinal veins. Right periureteric 

 venous ring present, through which ureter passes 



Type ABC (A, B, and C in fig. 1). Figure 11, cat (Darrach Series) 



Figure 11 shows a case in which the vena cava posterior 

 is represented in the lumbar region by three para-aortic 

 channels, which enclose a right and a left venous ring. On 

 the right side the ureter passes through the ring, establishing 

 a typical periureteric venous ring. On the left side, however, 

 the ureter extends between the kidney and the bladder with- 

 out passing through the left venous ring. The relations which 

 the ureters bear to the venous rings clearly indicate that the 

 veins which form the rings have been derived from the right 

 posterior cardinal and the right and the left supracardinal 

 veins. The left para-aortic channel (left supracardinal 

 vein) joins the right supracardinal, dorsal to the aorta, at a 

 level somewhat caudal to that of the renal veins. This indi- 

 cates that only a caudal section of the left lumbar supracar- 

 dinal is concerned, and that by means of an intersupracanli- 

 nal anastomosis, at a low level, it has retained a connection 

 with the right supracardinal vein (I nt.Sprc.Anast., fig. 1). 



So far as we can determine, the example illustrated by 

 figure 11 is the only instance in which Type ABO has been 

 described in the adult cat or in any other mammal. 



4. Persistence of right posterior cardinal, right supracardinal, 



left supracardinal, and left posterior cardinal r< 

 Right and left periureteric reiioiix riiif/x i>n . tit , tin 

 which ureters pass 



Type A BCD (A, B, C, and D in fig. 1) 



So far as we are aware, no instance of Ti// Ah('I) has 

 rvrr been described, either for the adult cat or for man. The 

 only case we know in which this type has been found to occur 

 in an adult mammal is that described by Hochstetter for 

 Erinaceus europaeus ('93, Taf. XXIII, fig. 24). Since Type 

 ABCD uniformly occurs as a transitory stage in the develop- 



