536 THE COMMON ILIAC VEINS. 



vein. It is obvious that .this condition would result from the foregoing variety if the vein of 

 the right side were obliterated. (J. Walter, " Ueber die partielle Verdoppelung der Vena cava 

 inferior," in " Beitrage zur Morphologic," &c., Stuttgart, 1884 ; A. Robinson, " Abnormalities 

 of the Venous System and their Relation to the Development of the Veins," in " Studies in 

 Anatomy," the Owens College, 1891.) 



In cases of transposition of the viscera, without other abnormality (p. 386), the inferior 

 vena cava is of course on the left side of the aorta throughout. 



In a few instances the inferior vena cava, instead of ending in the right auricle of the 

 heart, has been seen following the course of the right, or even of the left, azygos vein, passing 

 through the diaphragm by the side of the aorta, and ascending through the posterior media- 

 stinum, to join the superior vena cava. which therefore returns the blood from nearly the 

 whole of the body. In these cases the hepatic veins do not join the inferior cava, 

 but form a trunk which opens into the right auricle at the usual place of termination of that 

 vessel. In this variety it may be supposed that the normal inferior cava has not been 

 developed, and that the blood is returned from the lower part of the body by a persistent 

 cardinal vein. 



Supernumerary renal vein* are occasionally met with, but not so frequently as super- 

 numerary arteries ; and one of these vessels on the left side may open into the corresponding 

 azygos vein, as may also the spermatic or suprarenal vein. In rare cases a left renal vein has 

 been observed entering the common iliac vein ; this may also be explained as the persistence 

 of a portion of the left cardinal vein distal to the junction of the renal vein. 



The hepatic veins have been seen opening independently by one or two trunks into the 

 right auricle ; and a single hepatic vein has been found to end in this way, or in the left 

 auricle (Breschet), or in the right ventricle of the heart, where its orifice was guarded by a 

 valve (Rothe). 



COMMON ILIAC VEINS. 



The common iliac veins are formed on each side by the confluence of the external 

 and internal iliac veins. Extending from the base of the sacrum upwards to near 

 the junction of the fifth with the fourth lumbar vertebra, at a point a little to the 

 right of the middle line, the two common iliac veins unite to form the inferior vena 

 cava. The right vein is shorter than the left, and is nearly vertical in its direction. 

 The right vein is placed behind, and then to the outer side of its artery ; while the 

 left vein is to the inner side of the left common iliac artery, and then passes behind 

 the right. These veins are usually destitute of valves, but in a few instances one 

 has been met with (Friedreich). 



LATERAL TRIBUTARIES. The ilio-lumbar vein collects branches from the 

 hinder part of the abdominal wall, from the muscles of the back, and from the 

 spinal canal, and emerges from beneath the psoas muscle to enter the lower part of 

 the common iliac vein. It communicates above with the lumbar, and below with 

 the lateral sacral veins. 



The middle sacral veins, two in number, ascend on the front of the sacrum 

 with the middle sacral artery, and join above into a single vessel which opens into 

 the left common iliac, or occasionally into the angle of union of the two large veins. 

 They anastomose freely with the lateral sacral veins, and by smaller branches with 

 the veins of the rectum. 



Varieties. The common iliac vein is sometimes divided into two vessels for a portion of 

 its extent. Absence of the common iliac vein of one or both sides has been met with, the 

 left external and internal iliac veins being continued upwards to enter the commencement of 

 the inferior cava, or (in one case) the two internal iliac veins being joined into a common 

 trunk which unites with the right and left external iliac veins to form the vena cava 

 (Gruber). 



VEINS OF THE LOWER LIMB AND PELVIS. 



The veins of the lower limb are divisible into two sets, those of the one being 

 deeply seated, those of the other running in the superficial fascia. All the veins of 

 the lower limb are provided with valves, and these are more numerous than in the 

 veins of the upper limb. The deep veins have more valves than the sub- 

 cutaneous set. 



