No. 399. ] FREQUENCY OF ABNORMALITIES. 193 
which is considerably cephalad of the normal point, and to 
result in relatively long common iliac veins (2), Figs. 6, 7. 
The writer was at first inclined to regard these three cases 
as instances in which the posterior division of the left posterior 
cardinal vein, instead of the “Connecting branch," persists as 
the functional left common iliac vein, and for the following 
reasons : : 
1. Because in one instance (Fig. 7) the middle sacral vein 
(5) opens into the angle of union of two veins, as in those 
cases in which both posterior cardinal veins persist (Fig. 1). 
2. Because the left ilio-lumbar vein (6), in all three cases, 
opens into the left common iliac (2) and not into the common 
postcava (1), as is normally the case in the cat. (See Figs. 6, 7.) 
3. Because the functional left common iliac vein (2), in all 
three cases, unites with the corresponding vein of the opposite 
side in front of the middle of the sixth lumbar vertebra and, 
in this respect, resembles the left posterior cardinal vein (17) 
in Fig. 4, which persists there, in addition to a left common 
iliac vein (* Connecting branch "). *In other words, if the left 
common iliac vein (2) were absent in Fig. 4, the latter would 
resemble, so far as the veins are concerned, the conditions met 
with in Fig. 6. 
One marked difference exists, however, between the relative 
position of the left common iliac (2) in the three cases cited 
above and that of the left posterior cardinal vein (17) in Fig. 4. 
In the latter the vein lies ventrad of the aorta, the position it 
should normally assume were the vessel a persistent cardinal 
vein. In the three other cases, of which Fig. 6 is an example, 
the aorta (8) lies ventrad of the vein, which should not be its 
position unless a transposition of the vessel has taken place, a 
circumstance incapable of proof. "Whatever the significance of 
this abnormality may be, it is certainly worthy of mention, for 
it further emphasizes the fact that variations of the postcaval 
Vein and its tributaries are of unusual frequency in the cat. 
3. THe MippLE SacraL VEIN (V. sacralis media) AND ITS 
RELATIONS TO THE VEINS OF THE PELvic ReGion. — Much has 
already been said concerning this vein, but its variations are so 
Pronounced, that it seems best to specify them more in detail. 
