Charles F. W. McClure 
195 
in the same (McClure, 03, Plates I, II and IV). The presence of a 
bifurcated postcava in the adult is easily explained on embryological 
grounds as the result of a non-fusion of the two veins (cardinal col- 
lateral) which normally form the postcava caudal to the spermatic veins. 
Text Figs. 14, 15, 16, 17 and 18 clearly show how variable the character 
RENAL OMPHALO 
MESENTERIC 
ARTERY 
LEFT 
RENAL 
~ARTERY 
RENAL 
RENAL 
VEIN 
AORTA 
POSTCAVA 
ANT. 
SPERMATIC 
ARTERY 
OF ADULT 2 
UROGENITAL 
ARTERY 
SPERMATIC 
CARDINAL 
COLLATERAL PEP 
CARDINAL 
URETER COLLATERAL 
POST CARDINAL COMMON 
ILIAC 
ARTERY 
EXT. ILIAC oY 
COMMON 
INT. ILIAC 
PUDENDO 
VESICALIS: 
INT. ILIAC 
CAUDAL 
Fie. 16. 
Ere. 16. 
OMPHALO 
RENAL MESENTERIC 
ARTERY ARTERY 
RENAL 
ARTERY 
RENAL 
AZYGOS 
POSTCAVA 
LEFT 
URETER UROGENITAL 
ARTERY 
POSTCARDINAL 
COMMON 
ILIAC 
RTERY 
EXT. ILIAC 
PUDENDO- 
PUDENDO EDEN 
Vesicnitic VESICALIS 
MEDIAL RING 
LATERAL RING 
CAUDAL 
ARTERY 
TATE. ALT = 
Reconstruction (slightly schematic) of the venous system of a 15 
mm. pouch young of Didelphys in which a postcava of Type II is already 
established. 
Hires 27. 
Ventral view. 
Reconstruction (slightly schematic) of the venous system of a 
15 mm. pouch young of Didelphys in which a postcava of Type lie Bwiseal: 
ready established. 
Ventral view. This figure also shows the ventral portions 
of the lateral rings into which the Vv. pudendovesicales open. 
of the fusion may be between the two cardinal collateral veins even 
before the adult stage is reached, as well as the formation of the for- 
amina, through which the posterior internal spermatic arteries pass. 
In the 17 mm. pouch young the cardinal collateral division of the 
