190 THE AMERICAN NATURALIST. [VoL. XXXIV. 
the right external iliac artery (9), Fig. 3, arises from the aorta. 
Although the connection of this third vessel with the middle 
sacral vein is abnormal, its relative position, and especially its 
connection with the right posterior cardinal at the above-men- 
tioned point, lead the writer to the conclusion that it is the 
* Connecting branch " (Verbindungsast) which normally grows 
between the veins of the left hind extremity and the right pos- 
terior cardinal vein, in correlation with the appearance of the 
permanent kidneys and the atrophy of the distal portion of 
the left posterior cardinal vein. This 
so-called ** Connecting branch," un- 
der normal conditions, becomes the 
left common iliac vein (V. iliaca 
communis sinistra) and returns the 
blood from the left hind extremity 
. to the postcaval vein. In this par- 
ticular instance, however, the vein 
does not connect with the veins of 
the left hind extremity, but arises 
from the middle sacral vein by 
means of two radicles that soon be- 
come confluent, Fig. 5 (2, sinistra). 
The significance of this unusual 
connection will be spoken of in con- 
i d E nection with the following topic. 
post. 18. N. obturatorius. For re- The second case met with by the 
maining numbers, see Fig. r. : 5 s i 
writer, in which the posterior car- 
dinal veins persist, together with the “ Connecting branch ds 
(V. iliaca communis sinistra), is represented by Fig. 4. 
In this instance the persistent left posterior cardinal vein 
(17) unites with the corresponding vein of the right side, oppo- 
site the middle of the sixth lumbar vertebra, and not, as in the 
preceding case, in the region of the kidneys. The left poste- 
rior cardinal is also here of less importance physiologically, as 
is indicated by its relative size, than either the right posterior 
cardinal or the left common iliac vein (2). It is evident, there- 
fore, that the bulk of the blood from the left hind extremity 
was carried to the common postcava, chiefly by the left common 
Sinistra. 
2 
