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



been derived from, the left posterior cardinal (D in fig. 1), 

 instead of from the left supracardinal vein (C in fig. 1). 

 This is evident from the fact that the left ureter passes dor- 

 sal to the left cava and emerges between the aorta and the 

 caval vein. On the right side the cava is normal, having been 

 derived from the right supracardinal vein (B in fig. 1), as 

 is indicated by the relation which the ureter bears to the 

 right caval vein. 



Darrach found only two examples of Type BD in his series 

 of 605 adult cats, and both of these are shown here in figures 

 46 and 47. So far as we know, Type BD has not hitherto 

 been described for cat or for man. 



In figure 46, the right supracardinal and the left posterior 

 cardinal veins are of equal caliber. As no communication 

 exists between the iliac veins of opposite sides, each cava 

 starts as a direct continuation of the common iliac vein. In 

 figure 47, the right supracardinal forms the larger of the two 

 caval veins. It starts from the iliac confluence and ascends 

 on the right side of the aorta, passing ventral to a large 

 aberrant renal artery. The left posterior cardinal, the 

 smaller of the two caval veins, starts from the left iliac vein 

 and ascends at first dorsal and then ventral to the ureter, to 

 join the right cava, ventral to the aorta, approximately at 

 the level of the renal veins. In both instances the sex veins, 

 except for their duplicity on the left side, present normal 

 relations to the caval veins. 



Figures 48 and 49 represent, respectively, the right and 

 the left sides of a reconstruction of the veins in a 23-mm. 

 cat embryo. As shown in the figures, the right supracardinal 

 (Sprc.Dext., fig. 48) and the left posterior cardinal veins 

 (Pc.Sin., fig. 49) are the only vessels (cavae) concerned in 

 returning blood to the intersubcardinal anastomosis (Int. 

 Subc.Anast., fig. 49) from the iliac veins. The type of vena 

 cava represented at this stage of development is, therefore, 

 Type BD a condition which may have been only transitory 

 in character or, if development had proceeded, might have 

 been carried into the adult stage. This 23-mm. cat embryo 



