158 STUDIES IN ADVANCED PHYSIOLOGY. 



veins, unite to form the descending vena cava. Into the 

 descending vena cava there opens usually right close to the 

 heart the large azygos vein, which brings the blood from 

 the back body wall to the heart. Into the right auricle 

 itself open several coronary veins. The blood is returned 

 from the limbs through the external saphenous vein and the 

 internal crural vein. These unite on entering the pelvic 

 region into the external iliac vein, which then joins with 

 the internal iliac vein, returning the blood from the pelvic 

 region to form the right or left common iliac vein as the 

 case may be, which then unite and form the ascending 

 vena cava. Into the ascending vena cava the large renal 

 veins pour the blood which has just been through the kid- 

 neys, while close to the heart several hepatic veins enter 

 it, bringing the blood which has just passed through the 

 liver. In the lumbar region branches connect the ascend- 

 ing vena cava with the azygos vein, thus enabling blood 

 from that region to reach the heart by either of two chan- 

 nels. 



THE PULMONARY CIRCULATION. 



The circulation of the blood through the lungs for pur- 

 poses of purification is designated by a special name, and 

 is called the pulmonary circulation. This consists of a 

 pulmonary artery springing from the right ventricle and 

 leading to the two lungs, and the pulmonary veins, from 

 three to five in number, which bring the blood back to the 

 left auricle after its oxygenation in the capillaries of the 

 lung. 



THE PORTAL CIRCULATION. 



In enumerating the veins which empty into the ascend- 

 ing vena cava, one is at first surprised that there are no 

 veins from the stomach, spleen, pancreas, or intestines. 

 The blood, however, which has been carried to these 

 organs is gathered up in a special vein called the portal 

 vein, which is, therefore, of course, made by the conjunc- 

 tion of the gastric vein, the splenic vein, the pancreatic 

 vein and the intestinal veins. This portal vein carries all 



