THE VERTEBRATE BODY 



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on either side of the chest. The bronchi branch and rebranch within 

 each lobe of the lungs and finally end in a cluster of alveoli. 



Our method of getting air into our lungs is quite different from that 

 of the frog. By raising the ribs and lowering the diaphragm we are 

 able to increase the size of the chest cavity. When this is done the lungs 

 expand and the pressure of the outside atmosphere forces air through 

 the nose or mouth to fill the extra space in the lungs which has been 



Fig. 23.7. Diagram to illustrate the method of respiration in man. When the chest is 

 expanded the chest cavity becomes larger and the lungs expand to fill it ; this draws 

 the air in through the nostrils. When the diaphragm is lowered the chest cavity also 

 becomes larger with a corresponding expansion of the lungs. Most persons use a 

 combination of the two methods in normal respiration. 



