850 THE VASCULAR SYSTEM. 
iliae artery, and then upwards behind the peritoneum and in front of the psoas 
muscle and ureter. The veins of the right side, ike the corresponding spermatic 
veins, also pass behind the termination of the ileum and the third part of the 
duodenum ; whilst the left veins, near the brim of the pelvis, pass behind the com- 
mencement of the pelvic colon. 
The two veins on each side ultimately fuse together to form a single terminal 
vein which ends, on the right side in the inferior vena cava, and on the left side in 
the left renal vein. As the left ovarian veins ascend on the psoas they receive 
tributaries from the iliac and pelvic colon. 
THE ILIAG VEINS. 
The common iliac veins (Figs. 572 and 587), right and left, are formed by the 
union of the corresponding external and internal ilac veins. Hach commences 
opposite the brim of the pelvis, immediately behind the upper part of the internal 
iliac artery of its own side, and both vessels pass upwards to the right side of the 
body of the fifth lumbar vertebra, at the upper part of which, just behind and to 
the outer side of the right common iliac artery, they unite together to form the 
inferior vena cava. 
The right common iliac vein (vy. iliaca communis dextra) 1s much shorter than 
the left ; it passes in front of the obturator nerve and the ilio-lumbar artery, and 
at first behind and then somewhat to the outer side of the corresponding common 
ihac artery. 
The left common iliac vein (v. iliaca communis sinistra) is much longer than 
the right, and is also placed more obliquely. It passes upwards and to the right, in 
front of the body of the fifth lumbar vertebra, and across the middle sacral artery. 
For some distance it runs along the inner side of the left common iliac artery, and 
then passes behind the right common iliac artery. It also passes behind the 
mesentery of the pelvic colon and the superior hemorrhoidal artery. 
Tributaries.—Each common iliac vein receives the corresponding external and internal 
iliac veins and the ilio-lumbar vein. The left common iliac vein receives in addition the 
middle sacral vein. 
The iliolumbar veins (vv. ilio-lumbales) receive tributaries from the iliac fossa, from 
the lower parts of the spinal muscles, and from the spinal canal. There is a single vein 
on each side which accompanies the corresponding artery. It passes behind the psoas 
muscle and terminates in the common iliac vein. 
Middle Sacral Veins.—The ven comites of the middle sacral artery commence by the 
union of tributaries which issue from the venous plexus in front of the sacrum, through 
which they communicate with the lateral sacral veins and receive blood from the sacral 
part of the spinal canal. They unite above into a single stem (vy. sacralis media), which 
terminates in the left common iliac vein. 
The internal iliac vein (v. hypogastrica, Fig. 569) is a short trunk formed 
by the union of tributaries which correspond to all the branches of the internal 
iliac artery, with the exception of the hypogastric or umbilical branch. 
It commences at the upper border of the great sciatic notch, and ascends to the 
brim of the pelvis, where it unites with the external iliac vein to form the common 
iliac vein. It lies immediately behind and slightly to the inner side of the internal 
iliac artery, 1s crossed exte rnally by the obturator nerve, and is in relation internally, 
on the left side with the pelvic colon, and on the 1 ight side with the lower part of 
the ileum. 
Tributaries.—The tributaries, which are numerous, are conveniently divisible mto 
extra-pelvic and intra-pelvic groups. 
The extra-pelvie tributaries are all parietal, and include the obturator, internal pudic, 
sciatic, and gluteal veins. 
Obturator Vein (v. obturatoria).—This vein is formed by the union of tributaries 
which issue from the hip-joint and from the muscles on the upper and inner part of the 
thigh. It enters the pelvis through the obturator foramen, runs backwards along the 
lateral wall lying on the pelvie fascia immediately below the corresponding artery, and, 
passing between the internal iliac artery on the ‘outside and the ureter on the imeides 
terminates in the internal iliac vein. 
