APPLIED PHYSIOLOGY 



stretched like rubber bags, when air is blown through the 

 trachea, and will contract to their former size when the air 

 has been let out. 



339. The chest or thorax. The lungs are covered by 

 the ribs, which are hinged to the spinal column behind, 

 and to the breastbone in front, so as to form a bony frame- 



Diagram of the air sacs in a man's lung. 



a smallest bronchial tube. 



b a"collection of air sacs cut lengthwise. 



c air sacs cut across. 



d connective tissue between the air sacs. 



Diagram of a frog's 

 lung. 



work inclosing a cavity called the chest or thorax. The 

 floor of the thorax is formed by a muscle called the 

 diaphragm, which is attached to the lower border of the 

 ribs, and arches upward. It is lined with a smooth and 

 shining serous membrane like peritoneum, called the 

 pleura. Each lung is covered with pleura also. 



340. Inspiration and expiration. Muscles connect and 

 cover the ribs. They raise the ribs and expand the chest. 

 The diaphragm flattens its arch and makes the chest 



