THE MAMMALIAX VENA CAVA POSTERIOR 37 



is therefore another instance of the potential character of 

 the embryonic venous system in relation to the establishment 

 of atypical forms of caval veins. 



13. Persistence of left supracardinal vein 



Type C (C in fig. 1). Figures 50 and 51, cat (Darrach Series) 



The vena cava posterior represented by Type C is a mir- 

 ror picture of Type B. In Type C the vena cava is a single 

 vessel, situated on the left side of the abdominal aorta, de- 

 rived from the left embryonic supracardinal vein (Cm fig. 1). 

 As in all cases where the cava has been formed by a supra- 

 cardinal, the ureter in Type C lies entirely free of the caval 

 vein. The left sex vein opens into the cava caudal to the 

 renal level, and the right sex vein opens usually into the 

 right renal (fig. 50), though occasionally into the caval vein 

 (fig. 51). 



Figure 52 represents the left side of a reconstruction of 

 the veins in a 45-mm. cat embryo. It is an example of a case 

 in which the left supracardinal vein (Sprc., fig. 52) has per- 

 sisted to form the caval vein (Type C). It is of special inter- 

 est as evidence that the opening of the left sex vein into the 

 cava, caudal to the level of the renal veins (R.V.), has been 

 brought about by an elongation of the lateral portion of the 

 renal collar (Subc.Sprc.Anast.), to the caudal border of which 

 the posterior cardinal vein (Pc), with its sex-vein tributary 

 (S.V.), is attached. 



The presence of a left-sided vena cava posterior of Type C 

 is of relatively frequent occurrence in the adult cat. It was 

 found by Darrach ('07) in twenty-one cases (3.4 per cent) of 

 his series of 605 adults. Also, it has been observed in the 

 cat by Gage ('98), McClure ('00), and Hunt ('19); and in 

 Didelphys virginiana by McClure ('03 and '06). Among the 

 earlier anatomists a left vena cava inferior (Type C) was 

 observed in man by Wrisberg in 1778 and by Morgagni in 

 1779. In more recent times it has been described as occurring 

 in man by Berthel ( '01), Cameron ( '11), Frankel ( '10), Georg 

 ('06), Gerard ('08), Gladstone ('12), Grimsdale ('94), Gruber 



