194 FREDERICK TILNEY 



to bridge the gaps between the earlier and the later stages in 

 certain regions, in which its preservation permitted definite 

 conclusions. 



In a single adult specimen of Tragulus, McClure ('06) found 

 that the post-renal division of the post-cava was placed directly 

 in front of the aorta and formed by the union of the common 

 iliac veins, this union taking place ventral to the aorta. These 

 relations correspond to one of the three types of post-cava de- 

 scribed by him ('03) in Didelphis marsupialis and figured in 

 his plate 2 as no. 8. McClure concludes that this condition 

 allies the venous organization of Tragulus more closely to that 

 of the marsupials than to any of the known ruminants. In 

 a verbal communication to the writer, Dr. McClure states that his 

 earlier observations have been confirmed by the subsequent exami- 

 nation of three additional adult specimens of the animal. 



Beddard ('07) observed the same relations of the aorta, to the 

 post-renal segment of the post-cava in three adult specimens of 

 Tragulus. One male adult and three male fetuses in the Col- 

 umbia collection show the post-renal segment of the post-cava 

 directly in front of the aorta. The conditions in the adult speci- 

 men are illustrated in fig. 1. In Tragulus the axial venous chan- 

 nel from the confluence of the internal and external iliac veins 

 (fig. 1, 36 and 37) to the renal level consists of two parts; a, 

 the common iliac veins (fig 1, 38) (paired portion of the post- 

 cava, this latter term being used to keep the account in accord 

 with McClure's description) and b, the unpaired portion of the 

 post-cava, ventral to the aorta (fig. 1, 39). The unpaired por- 

 tion is 6.5cm. in length and extends from the confluence of the 

 common iliac veins to the renal anastomosis. The common 

 iliacs are 4.9 cm. in length and extend from the confluence of 

 the internal and external iliac veins to the paired portion of the 

 post-cava. Each common iliac vein receives the sex vein of 

 the corresponding side (fig. 1, 40). Tragulus differs, in this 

 respect, from the majority of marsupials in which the sex veins, 

 as has already been shown by Schulte ('07) and Schulte and 

 Tilney ('09), empty into the unpaired portion of the post-cava 

 or into the post-cava and left renal vein. 



