192 



ADVANCED PHYSIOLOGY 



contract and lift the ribs, the chest cavity is enlarged and as 

 a result air will be drawn in to fill the enlarged space. This 

 forcing of the air into the lungs is called an inspiration. When 

 later the ribs fall downward again the chest cavity is con- 

 tracted and the air is forced out, producing an expiration. 

 It is a muscular effort to raise the ribs and inspire air, but they 

 fall back, in part at least, of their own weight. 



FIG. 102. DIAGRAM 



Illustrating the mechanism of diaphragm breathing. It represents the lungs of soi 

 small animal in a closed bell glass. As the rubber membrane below is pulled dc 

 enlarging the cavity, air rushes in through the tube that represents the tracl 

 and the lungs enlarge. (Tigerstedt) 



Diaphragm Breathing. When at rest the diaphragm is m 

 stretched across the bottom of the thoracic cavity in a flat 

 plane, but arches upwards on all sides; Fig. 46, page 89. 

 Its shape thus causes it to project into the thorax and decrease 



