156 ELEMENTS OF MAMMALIAN ANATOMY. 



bar muscles empty into the vena cava a centimeter or more 

 cephalad to the large common iliacs. The union of the com- 

 mon iliac veins collecting the blood from the hind-limbs and 

 the pelvic region, and the caudal vein, forms the begin- 

 ning of the postcava. 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 intestines; the g astro splenic, 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 pancreato- 

 duodenalis, from the pancreas and duodenum. The last 

 three may empty directly into the portal vein or into 

 one of the three branches first named (Fig. 76). 



The superior vena cava extends from the union of the 

 brachiocephalic veins to the right auricle. Three im- 

 portant veins empty into the precava: the azygos, col- 

 lecting 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 vertebrarterial canal of the 

 first six cervical vertebrae. The left vertebral vein is a 

 tributary of the left brachiocephalic (Fig. 76). 



The brachiocephalic vein is formed by the union of the 

 subclavian and the external jugular. Sometimes the ver- 

 tebral vein joins also in the union instead of emptying 



