146 



OUR BODIES AND HOW WE LIVE 



FIG. 90. 



204. The Veins. The veins are the return pipes that 

 bring the blood Back to the heart. They generally lie 

 near the surface of the body, just beneath the skin. We 

 may see them in almost any part of the body. Unlike 

 the arteries, which gradually grow 

 smaller and smaller, the veins, start- 

 ing from the capillaries, grow larger 

 and larger. 



The veins of the legs pass upwards, 

 becoming gradually larger by the addi- 

 tion of other branches in the abdomen, 

 until at last all the united branches 

 are joined in one great vein, which 

 empties into the right auricle of the 

 heart (Sec. 202). 



The venous blood from the head 

 B, longitudinal section of and the arms empties into the right 



a vein, showing the valves -11 ^11 



closed< auricle by another large vein. 



As we have learned, the four pul- 

 monary veins carry the arterial blood from the lungs to the 

 left auricle (Sec. 202). 



The veins are abundantly supplied with little pouch- 

 like folds or pockets which act as valves to prevent the 

 backward flow of the blood. If we press the fingers 

 along one of the veins in the arm, towards the hand, we 

 shall see a number of little knots or swellings here and 

 there along the vein. These indicate the position of the 

 valves. 



The blood thus forced back fills the little pockets in the 

 vein. Take away the finger and the knots will at once 

 disappear, because the blood is left free to flow towards 

 the heart. 



