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THE PORTAL VEIN 693 
The mode of origin is variable. In some cases there is a common trunk formed by the 
union of the two internal iliac veins so that the arrangement resembles the termination of the 
aorta. In other cases the internal iliac vein does not exist. Exceptionally there is a small middle 
sacral vein on the middle of the pelvic surface of the sacrum. It opens at the angle of divergence 
of the common iliac veins. 
It passes forward on the ventral face of the psoas minor to the right of the 
abdominal aorta. At the last thoracic vertebra it separates from the aorta and 
runs forward between the right crus of the diaphragm and the pancreas till it 
reaches the liver. Here it inclines ventrally along the medial border of the right 
lobe and on the parietal surface of the liver, largely embedded in the gland sub- 
stance, and passes through the foramen ven cave of the diaphragm. It then runs 
forward and somewhat ventrally between the intermediate lobe and the main mass 
of the right lung at the upper margin of a special fold of the right pleura, accom- 
panied by the right phrenic nerve, and opens into the posterior part of the right 
atrium opposite the fifth intercostal space. It receives the following tributaries: 
1. The phrenic veins (Vv. phrenicze), two or three in number, return the blood 
from the diaphragm. They are very large in comparison with the arteries, and 
join the vena cava at the foramen ven cave. 
2. The lumbar veins (Vy. lumbales) correspond to the arteries. Five pairs 
usually empty into the posterior vena cava. Sometimes the corresponding veins 
of opposite sides unite to form a common trunk. The first communicate with the 
vena azygos or hemiazygos, and the last usually enters the common iliac vein. 
3. The internal spermatic veins (Vv. spermatic interne) (Fig. 575) accompany 
the arteries of likename. In the spermatic cord they form a very rich network, the 
pampiniform plexus (Plexus pampiniformis) about the artery and nerves. Their 
termination is variable. The right one commonly joins the vena cava near the 
renal vein, often by a common trunk with the left one. Frequently the left vein 
joins the left renal, and sometimes the right one ends similarly. 
3a. The utero-ovarian veins are much larger than the preceding and are 
satellites of the arteries in the broad ligaments. The ovarian branch is plexiform 
near the ovary. The uterine branches form a rich plexus in the wall of the uterus. 
The trunk is very short and terminates like the corresponding vein of the male. 
4. The renal veins (Vv. renales), satellites of the arteries, are of large caliber 
and thin walled. The right vein passes medially and backward on the ventral face 
of the kidney, between the artery in front and the ureter behind. It joins the vena 
cava above the right adrenal. The left vein is somewhat longer. It passes medially 
at first like the right one, then bends around the posterior end of the adrenal, crosses 
the origin of the renal artery, and opens into the vena cava a little further back than 
the right one. They receive veins from the adrenals, but some adrenal veins (Vv. 
adrenales) open directly into the vena cava. 
5. The hepatic veins (Vv. hepatice) return the blood from the liver, and open 
into the vena cava as it lies in the groove in the liver. Three or four large veins 
open into the vena cava just before it leaves the liver, and numerous small ones 
discharge into its embedded part. 
Of the foregoing, the phrenic and lumbar veins are termed parietal radicles 
(Radices parietales), and the remainder are visceral radicles (Radices viscerales). 
THE PORTAL VEIN 
The portal vein (V. porte) is a large trunk which returns the blood carried to 
the viscera by the gastric, splenic, and mesenteric arteries; its average diameter is 
a little more than an inch (ca. 3 cm.). Its peripheral tributaries correspond closely 
with the branches of the arteries, but the trunks do so in part only. The vein is 
formed behind the pancreas and below the posterior vena cava by the confluence 
of the anterior and posterior mesenteric and splenic veins. It passes forward, 
