PORTAL SYSTEM 155 



behind the pancreas and the last part of the duodenum. The 

 right renal vein passes behind the duodenum. 



The Lumbar veins, of which there are four pairs, are formed 

 by tributaries from the lateral and posterior walls of the ab- 

 domen. They are also connected together by the azygos veins, 

 .anastomosing vessels passing upwards. 



The Spermatic or Ovarian veins are formed by the pampini- 

 form plexuses surrounding the testicles or ovaries. The vein 

 on the right side enters the inferior vena cava, that on the left 

 usually enters the left renal vein. 



The Common Iliac veins are formed by the union of the 

 external iliac and internal iliac veins opposite the brim of the 

 pelvis behind the internal iliac artery. They pass upwards and 

 inwards, and unite to form the inferior vena cava opposite the 

 fifth lumbar vertebra. 



Tributaries. External iliac. 

 Internal iliac. 



Ilio-lumbar, small veins from the iliac fossa and 

 adjacent parts. 



The Internal Iliac vein is formed at the upper border of the 

 great sciatic notch by the union of veins corresponding to the 

 branches of the internal iliac artery, except the ilio-lumbar 

 branches. It lies behind and slightly to the inner side of the 

 corresponding artery. 



The External Iliac vein is the continuation of the femoral vein, 

 :and commences on the inner side of the femoral artery. 

 Passing upwards and inwards along the brim of the pelvis, it 

 ends by joining the internal iliac to form the common iliac 



The Portal System. The portal vein is formed by tribu- 

 taries from the whole of the alimentary canal (except the lower 

 part of the rectum), the spleen and the pancreas, and conveys 

 the blood thus collected to the liver. The tributary veins corre- 

 spond at first with the arteries supplying these organs, but the 

 terminal veins differ somewhat. The inferior mesenteric vein 

 joins the splenic vein, and they join with the superior mesentric 

 Tein to form the portal vein. The portal vein is a short wide 

 vessel about three inches long, which commences behind the 



