44 ANATOMY. 



The apex is the point at the front part of the lung. 



The base rests against the diaphragm. 



The bronchi are subdivided until they are very small and 

 are then called bronchioles. Each bronchiole terminates in a 

 very small cavity made by a lot of air cells opening together. 

 These cells have very thin walls and are separated by loose con- 

 nective tissue, in which minute blood vessels are located. Blood 

 is then separated from the air by only a very thin membrane. 



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