RESPIRATION 



35 



change in pressure? It depends upon the situation of 

 the lungs in the body. If we disregard the legs, arms, 

 and head, the body is like a barrel. The hollow space 

 inside contains various organs busy with the life proc- 



Fig. 20.— Front view of trachea and its branches. Ep., Epiglottis; Lar. t Larynx; 

 Th., Thyroid Cartilage; Or., Cricoid Cartilage; R., Ring of Cartilage; B.I., 

 Left bronchus ; C, Chest wall and ribs. (From Fitz.) 



esses. In higher animals this cavity has a partition 

 stretched across it. This partition regulates to a great 

 extent the pressure in the lungs. It is not an immov- 

 able partition, but one that is capable of a great deal of 

 activity. It is made of a muscle called the diaphragm 

 in which the fibers are arranged like the radii of a 



