CIRCULATION OF THE BLOOD. 103 



capillaries, in every part of the body. From these vessels the 

 blood flows into the minute extremities of the veins, and 

 thence into the larger branches, and finally into the great 

 vena cava, which pours the blood into the right auricle of 

 the heart. 



22*2. The arteries carry the nutritious blood to support the 

 life of the textures. If they are wounded, serious conse- 

 quences follow, and they are not very readily healed. They 

 are therefore placed deeply within the flesh, where they are 

 protected from injury. Some of them approach the surface, 

 and their pulsations can be felt at the wrist, and at the sides 

 of the neck, and on the temple. 



223. The veins carry the impure and wasted blood. They 

 suffer less, and are more easily healed, than the arteries when 

 injured. Their great trunks are placed* near the great arte- 

 ries, but their branches are situated nearer to, and more of 

 them on, the surface, than the arterial branches. They are 

 seen on the back of the hand and on the arms ; and sometimes 

 they enlarge and become very troublesome on the skin of 

 the lower limbs. Bleeding is usually performed by opening 

 a vein of the arm*. 



224. The blood passes out from the left side of the heart 

 through the arteries to the body, and returns through the 

 veins to the right side of the heart. These two sides are 

 separated by an impassable wall, (Fig. VIII. c.) Before 

 the blood can reach the left side of the heart, it must pass 

 through the lungs. This passage of the blood through the 

 lungs constitutes what is called the pulmonary circulation. 



225. The pulmonary artery passes out from the right ven- 

 tricle, (Fig. VIII. 6,) and divides into two branches, (Fig. 

 VIII. k, &,) one of which goes to the right lung, and the 

 other to the left lung. These divide, and finally spread their 

 minute branches throughout the substance of the lungs. 

 The pulmonary veins begin very minute in all the parts of 

 the lungs, where the little arteries terminate. These little 

 vessels unite again and again, until they form one large vein 



