THE MAMMALIAN VENA CAVA POSTERIOR 33 



dorsal to the aorta, is determined in individual cases by the 

 level at which an intersupracardinal anastomosis (Int.Sprc. 

 Anast., fig. 1) has been retained. In the composite diagram 

 of the veins, figure 1, the line of development followed by 

 the left cava in figures 38, 39, and 40 is along C, which, at 

 different levels in individual cases, retains a connection, dor- 

 sal to the aorta, through an intersupracardinal anastomosis 

 (Int.Sprc.Anast.) with the right supracardinal vein (B}. 



The variants shown of Type B in figures 41, 42, and 43 

 differ from those just described only in the presence of an 

 additional anastomosis, dorsal to the aorta, at the iliac level 

 (left common iliac vein in fig. 41), or, at the level of the ilio- 

 lumbar veins (figs. 42 and 43), between the axial veins of 

 opposite sides. If an anastomosis between the veins had not 

 been established at the iliolumbar level in the variants shown 

 in figures 42 and 43, there would have resulted an elongated 

 left common iliac vein, similar to that seen in figure 40. 



A double or paired vena cava posterior in the lumbar 

 region (Type BC, fig. 1) is of relatively common occurrence 

 as a variant both in the adult cat and in man, and is a type of 

 cava normally met with in a number of mammalian forms. It 

 has been found to occur normally in the adult of Phoca com- 

 munis (von Baer, '35), Chalamydophorus truncatus (Hyrtl, 

 '55), Phoca (spec.?), Halichoerus truncatus (Burow, '38); 

 Phoca vitulina, Delphinium delphis, Dasypus setosus, Dasy- 

 pus novemcinctus, Manis gigantea, Erinaceus europaeus, 

 Pteropus edulis, Echidna setosa (Hochstetter, '93) ; Oryc- 

 teropus (Beddard, '09), and probably in the elephant (Hunt- 

 ing-ton and Mr< lure). 



In mammals other than man, a double posterior vena cava 

 has been described occurring as a variant in the dog by Kerk- 

 ring (1670); in the cat by Gage ('98), McClure ('00), Dar- 

 rach ( '07), Smallwood ( '06), and Metcalf ( '18) ; in Hylobates 

 by Keith ('96); and in Pidelpliys virginiana l>y McClnn- 

 ('03 and '06). 



Among the early anatomists who have described or figured 

 a double vena cava inferior as occurring in adult man are: 



MEMOIR 15 



