THE MAMMALIAN VENA CAVA POSTERIOR 19 



or more (fig. 7) of the subcardino-posterior cardinal anasto- 

 moses (Subc.Pc.Anast., fig. 1) caudal to the renal level, be- 

 tween the right subcardinal (Subc.) and the right posterior 

 cardinal , veins (A, fig. 1). The left sex vein of the cat is 

 formed by the subcardinal plexus of the left sex gland (S.V.), 

 by a left subcardino-posterior cardinal anastomosis (Subc.Pc. 

 Anast. Sin., fig. 1), and by a segment of the left posterior 

 cardinal vein (D, fig. 1). At the renal level the latter joins 

 the left subcardino-posterior cardinal anastomosis (Subc.Pc. 

 Anast.) which, after atrophy of the left side of the renal 

 collar (Sub c.Sprc. Anast. Sin.), becomes the proximal portion 

 of the left renal vein of the adult. Figure 5, which represents 

 a stage of development in which the left side of the renal 

 collar has completely disappeared (Sub c.Sprc. Anast.), makes 

 plain the composition and the relations of the left sex vein 

 in the adult cat. Figure 5 should be compared with figure 3, 

 in which is present the left side of the renal collar. 



Type A was found by Darrach in twenty-two, or 3.6 per 

 cent, of the 605 adults examined. It has been figured as occur- 

 ring in the cat by Hochstetter ('93) and Gage ('98); in the 

 cat and the rabbit by Graves and Davidoff ( '22) ; and in man 

 by Hochstetter ('93), Huntington ('07), Kolisko ('09), MIM! 

 Gladstone (11). 



2. Persistence of right posterior ranlum! niul rif/lif 



supracardinal veins. Right periureteric venous 



ring present, through which ureter passes 



Type AB (A and B in fig. 1). Figures 9 and 10, cat (Darrach Series) 



This interesting variant (figs. 9 and 10) shows a condition 

 in which the right ureter passes through a periureteric venous 

 ring. The dorsal circumference of this venous ring is 

 formed by the right supracardinal vein: its ventral circum- 

 ference, which receives the right sex vein, is formed by the 

 right posterior cardinal. As shown in the composite dia- 

 gram (fig. 1), the periureteric venous ring is due to the per- 

 sistence of A and B ; the common trunk cranial to the venous 

 rin.ir, between the ring and the renal veins ( /M'.), IIMS resulted 



