r 44 ELEMENTS OF MAMMALIAN ANATOMY. 



iliacs. The union of the common iliac veins collecting the 

 blood from the hind-limbs and the pelvic region, and the 

 caudal vein, forms the beginning of the inferior vena cava. 

 The common iliac is formed by the union of the external 

 and internal iliac veins in the pelvis. The former is much 

 the larger of the two. 



The portal system begins with the veins collecting the 

 blood from the intestines, pancreas, spleen, and stomach, 

 and terminates where the hepatic veins enter the vena cava. 

 The inferior mesenteric vein collects the blood from the 

 large intestine; the superior mesenteric, from the small in- 

 testines; the gastrosplenic, from the spleen, stomach, and 

 pancreas; the coronary, from the lesser curvature of the 

 stomach; the gastro-epiploica, from the greater curvature 

 of the stomach; and the pancreatoduodenalis, from the pan- 

 creas and duodenum. The last three may empty directly 

 into the portal vein or into one of the three branches first 

 named (Fig. 78). 



The superior vena cava extends from the union of the 

 innominate veins to the right auricle. Three important veins 

 empty into the superior vena cava : the azygos, collecting 

 blood from the intercostal spaces; the sternal, lying on the 

 visceral surface of the sternum; and the right vertebral, 

 which, with its fellow, collects the blood from the deep 

 muscles and spinal cord in the region of the atlas, and after 

 making a strong anastomosis with the internal jugular vein, 

 descends in company with the vertebral artery through the 

 transverse foramina canal of the first six cervical vertebrae. 

 The left vertebral vein is a tributary of the left innominate 

 (Fig. 78). 



The innominate vein is formed by the union of the subcla- 

 vian and the external jugular. Sometimes the vertebral vein 

 joins also in the union instead of emptying into the superior 

 vena cava. The subclavian vein returns the blood from the 



