THE VEINS 



THE Veins convey the blood from the capillaries of the different parts of the 

 body toward the heart. They consist of two distinct sets of vessels, the pulmonary 

 and systemic veins, and an appendage to the systemic, the portal system. 



The Pulmonary Veins are concerned in the circulation of the blood through the 

 lungs. Unlike other vessels of this kind, they contain arterial blood, which they 

 return from the lungs to the left auricle of the heart. 



Ftc,. 489. Valves of a vein. In the lower part 

 of the figure are seen the parietal valves; the 

 upper part shows the mouth of a vein guarded 

 y a valve. (Poirier and Charpy.) 



FIG. 490. Collateral anastomosis of veins. The arrows 

 indicate the direction of the flow of blood (schematic). 

 (Poirier and Charpy.) 



The Systemic Veins are concerned in the general circulation; they return the 

 r enous blood from the body generally to the right auricle of the heart. 



The Portal Vein and its radicles constitute the portal system. The portal system 



in reality an appendage to the systemic venous system, and is confined to the 

 ibdominal cavity, returning the venous blood from the viscera of the digestive 

 ystem, and carrying it to the liver by a single trunk of large size, the portal vein. 

 This vessel ramifies in the substance of the liver and breaks up into a minute 

 letwork of capillaries. These capillaries then re-collect to form the hepatic veins, 

 )y which the blood is conveyed to the inferior vena cava. 



The veins, like the arteries, are found in nearly every tissue of the body. They 

 jommence by minute plexuses which receive the blood from the capillaries. The 



(707) 



