398 Venous System of Didelphys Marsupialis 
attachment of the intestines. In the writer’s estimation its absence is 
more likely related to the circumstance that the postcava in marsupials 
is closely applied to the ventral surface of the aorta at the point from 
which the posterior mesenteric artery should arise, and may thereby 
prove a hinderance to the development of this artery. 
ON THE PRESENCE OF A BIFURCATED PosTCAVAL VEIN IN Didelphys. 
In about forty-two (42) per cent of the adult opossums examined by 
the writer, as shown in the following table, the postcaval vein was either 
bifureated as far craniad as the internal spermatic veins, or presented 
some indications of an incomplete fusion between the two vessels which 
form the posteava caudal to the internal spermatic veins. 
Type III. 
| Type I. | Type II. A. B C Bove! 
| Ge Pl Ce G5 CSOs Sion ee 
| r i 
Posteava bifurcated as far 
craniad as the Vv. sper- | | 
MENA 55 Ganuocagunodead es es Uesaitmad I 2 4 1 ] 21 
| 
Postcava partially bifurcated) | 
Candad at Wr spermatice: |i.) eq) eee.) a) Pie) socal ieee 5 
Foramen in postcava at level, | 
of Vv. spermatice, and | 
postcava bifurcated caudad | | | 
OfSAMe near kee te Fey See ee ei eareliedouiimcwle an |) =| 9 
Foramen in postcava through | | | | 
which an A. spermatica | | 
PASSES. eee er ce eat Ne Neate lal 2 a 
TRE RE iss) SEE eT 3. HON ie mab 
GEIS es chaceyc citenssas = —— 2 
aoe 3 2 1 re) 6 . 
In twenty-one (21) opossums (8 males and 13 females) the posteava 
was bifurcated as far craniad as the internal spermatic veins and it is 
important to note that this is as far craniad as the bifurcation reached 
writer (Text Fig. VI). In Didelphys the anterior pair of spermatic arteries are not, as 
arule, as large as the posterior pair although they may attain this size during the 
breeding season. In most cases the anterior spermatic arteries do not extend as far 
as the ovaries or testes but anastomose with the posterior pair of spermatic arteries 
as represented in Text Fig. V of Petrogale (right side), The two pairs of spermatic 
arteries are represented in Fig. 23, Plate V and in Text Figs. VI, VII and IX, 
