No. 399.] FREQUENCY OF ABNORMALITIES. 195 
The foramen, which, in both cases, was situated near the 
juncture of the external and internal iliac veins, was complete, 
so that the artery could be dissected away from the vein with- 
out injuring the latter. After passing through the foramen 
the artery naturally lies dorsad ‘of the vein, but in its subse- 
quent course assumes its usual position at the side of the 
vein. 
Two cases were met with, in which the left internal iliac 
artery passed through a foramen in the left common iliac vein. 
Since there is no essential difference between any of these four 
cases, so far as the character and relative position of the foram- 
ina are concerned, Fig. 8 will serve as a description for all. 
Treadwell! has described an abnormality as occurring in the 
cat somewhat similar to these four cases described above, but 
on account of the poor condition of his preparation, he was 
unable to locate accurately the exact position of the foramen. 
An examination of his figure leads the writer to the conclu- 
sion that his preparation is similar, in every respect, to that 
represented above by my Fig. 8. 
The two cases in which a lumbar ártery passed through a 
foramen in the postcaval vein resemble those mentioned above, 
so far as the completeness of the foramina is concerned, and, 
therefore, need no further mention. It is interesting to note, 
however, that in each instance the vein was penetrated by the 
same lumbar artery, the artery situated just cephalad of the 
ilio-lumbar artery. 
(6) Foramina, when present, were not exclusively connected 
with the transference of arteries. In three cats both obturator 
nerves (18), Fig. 5, were found to pass through foramina situ- 
ated at the point where the external and internal iliac veins 
unite, 
The foramina in each instance were complete, and, as in the 
Case of the arteries, the nerves were easily dissected away 
without injuring the veins.? 
! Anat. Anz., Bd. xi, p. 717 
* Ogle (Journ. of Anat. and Phys., vol. xxix) describes a case as occurring in 
man, in which the left hypoglossal nerve pierced the wall of the left vertebral 
