The =posterior vena cava= (V. cava caudalis) returns almost all of the
blood from the abdomen, pelvis, and pelvic limbs. It is formed by the
confluence of the right and left common iliac veins at the fifth lumbar
vertebra, above the terminal part of the aorta and chiefly to the right
of the median plane.
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.
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 downward along the
inner border of the right lobe and the parietal surface of the liver,
largely embedded in the gland substance, and passes through the foramen
venæ cavæ of the diaphragm. It then runs forward and somewhat downward
between the mediastinal lobe and the main mass of the right lung at the
upper margin of a special fold of the right pleura, accompanied by the
right phrenic nerve, and opens into the posterior part of the right
atrium. It receives the following tributaries:
1. The =lumbar veins= (Vv. lumbales) correspond to the arteries. Five
pairs usually empty into the vena cava. Sometimes the corresponding
veins of opposite sides unite to form a common trunk. The first
communicate with the vena azygos.
2. The =spermatic veins= (Vv. spermaticæ internæ) (Fig. 450) accompany
the arteries of like name. In the spermatic cord they form the
pampiniform plexus 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.
2_a_. 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.
3. The =renal veins= (Vv. renales), satellites of the arteries, are of
large caliber and thin-walled. The right vein passes inward 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 inward 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 open directly into the vena cava.
4. The =hepatic veins= (Vv. hepaticæ) 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 vessels open into the vena cava just before it leaves the
liver, and numerous small ones discharge into its embedded part.
5. The =phrenic veins= (Vv. phrenicæ), 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 as it lies in the caval opening.
In some cases there is a small middle sacral vein (V. sacralis media),
a satellite of the artery. It opens into the angle of junction of the
common iliac veins or into one of the latter.