392 Venous System of Didelphys Marsupialis 
found in Petrogale and other marsupials than those of any of the other 
Types. In each ease the affluent veins of the postcava unite to form the 
latter on the ventral surfaces of the arteries, but the manner in which 
the union takes place is not the same. In Petrogale, etc., two Vv. ilace 
communes unite to form the postcava (Text. Fig. VI), while in Didelphys 
it is usually formed through the union of a V. iliaca interna communis 
with one (Fig. 4) or both (Figs. 2 and 3) of the Vv. iliace externe. 
It is worthy of notice in this connection that in Petrogale, etc., a 
Truncus hypogastricosacralis” and two Vy. iliace communes are the 
rule, while in Type I the reverse conditions usually prevail, namely, a 
V. hypogastricosacralis and two Aa. iliace communes. 
One of the most interesting as well as remarkable features of this and 
all of the other Types is the number of variations that occur within the 
Type. Figs. 1, 2, 3 and 4 represent the most common of the variations 
that were met with under Type I, but by no means include them all.” 
Type IT.—Includes those cases in which the Vv. iliace interne 
unite with the Vv. iliace externe to form the postcava, dorsal 
to the Aa. iliace communes or dorsal to the aorta. 
Twenty-seven examples of this Type were met with distributed among 
nine males and eighteen females. 
See Figs. 6, 7, 8, 9 and 10 (ventral views), Plate les 
Two principal sets of variations were met with within this Type: 
First, in which the internal iliac veins join both the right and left 
external iliac veins to form common iliac veins. In this set of variations 
the internal iliac veins may (Figs. 6 and 7) or may not (Fig. 8) anas- 
tomose with each other ventral to the A. sacralis media before joining 
the external iliac veins. The internal iliac veins may also, at the point 
where they join the external iliac veins, be subequal (Figs. 6 and 8) or 
very unequal (Fig. 7) in calibre. In the latter case (Fig. 7) the blood 
from the internal iliac veins is returned to the postcava chiefly through 
the right common iliac vein. 
Second, as in Figs. 9 and 10, in which the internal iliac veins anasto- 
mose with each other ventral to the A. sacralis media and then open by 
16In the wombat dissected by the writer, two common iliac arteries instead of a 
Truncus hypogastricosacralis Were present. 
In a few individuals examined (Fig. 3) the spermatic artery (A.s.i.p.) arose by a 
single trunk from the right side of the aorta apd soon divided into three branches. 
Two of these ran to the ovaries in the usual manner. The third, however, extended 
caudad on the ventral surface of the posteava and then divided, on each side, into 
two branches which ran respectively to the psoas muscle (ps.) and the bladder (bl.) 
The last mentioned branch followed the ureter. 
