RESPIRATION. 



93 



of capillaries, and it is here the dark, impure blood, while 

 passing through, parts with the carbonic acid, and in return 

 receives from the air the required oxygen. As in the general 

 system, this network collects into larger vessels, and the 

 blood, now changed to a bright red color, passes on through 

 the pulmonary veins into the heart. 



FIG. 30. Outline of the Lungs, with the Larynx, Windpipe 

 and Bronchial Tubes. 



4. The Air Passages. Extending from the back of the 

 tongue to the root of the lungs are the air passages, through 

 which the air rushes in each act of breathing. The first part, 

 the trachea, is a single tube, which divides into two branches 

 at the lower part of the jieck, one for each lung. Each 



