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Venous System of Didelphys Marsupialis 
In all marsupials hitherto examined, with the possible exception of 
Petaurus taguanoides (Hochstetter, 93), the postrenal division of the post- 
cava lies ventral to the aorta and, in this respect, forms an exception 
to the conditions met with in other mammals in which a single postcava 
is normally present. This unique position assumed by the postcava in 
marsupials was apparently first observed by Owen in 1866 in the wombat 
and kangaroo, although it is due to Hochstetter’s more recent investiga- 
tions that it may be regarded as characteristic of the marsupials in 
general. 
In its position, ventral to the aorta, 
the postrenal division of the postcava of 
Didelphys marsupialis agrees with that 
of other marsupials. It differs from 
these, however, in one particular feature, 
namely, in the variable manner in 
which: its posterior tributaries 
(Vv. ilhace) unite to form the post- 
cava. 
In order to understand these remark- 
able variations in Didelphys it will be 
necessary first to consider the anatomy 
of the postrenal division of the postcava 
in other marsupials where, so far as 
known to the writer, its mode of origin 
is uniform. 
In a wombat (Phascolomys mitchellt) 
and a wallaby [Petrogale (spec.?) ] 
Fic. VI. Postrenal division of the 
posteava of Petrogale (spec.?). Ven. recently dissected by the writer the post- 
tral view. : : 
A.i.e., A. iliaca externa; A.ii., A. CAVa Was formed, in each animal, 
iliaca interna; A.m., A. mesenterica; ° Te *7: 
Ao., aorta: A.r., A.tenalis: A.s.ia.A. through a union of the Vv. iliace com- 
spermatica interna anterior; A.s.i.p., 7 8 : : i : 
A. spermatica interna posterior: aere munes (V.i. c. in Text Fig. VI), which 
posteava; T.hs., Truncus hyp: gastri- nese 
cosacralis; V.ie., V. iliaca’ externa: 00k place ventral to the arteries. Also, 
vali’ Visp ey terna: Venez’ in each animal, between the Truncus 
hypogastricosacralis (T. hs.) and the A. 
renalis (A. r.) the postcava was situated in the middle line and ventral to 
the aorta (Ao.). In Petrogale the Vv. spermatice interne (V. sp. i.) 
opened into the posteava, as in Didelphys, slightly caudad of a point mid- 
way between the Vv. renales (V. r.) and the Vv. iliace communes 
(V.i.¢.). In the wombat, however, the spermatic veins opened into the 
posteava slightly caudad of the renal veins.“ Whether this connection, 
In the wombat the spermatic arteries also arose in the neighborhood of the 
kidneys. 
