BREATHING.] 



PHYSIOLOGY, 



95 



This is what does take place in breathing or respira- 

 tion. Every few seconds, about seventeen times a 

 « minute, the diaphragm does descend, and a quantity of 

 \ air rushes into the lungs through the windpipe. This 

 is called inspiration. As soon as that has taken 

 place, the diaphragm ceases to pull downwards, the 



\ 





Fig, 12. — The Diaphragm of a Dog viewed from the Lower or 



Abdominal Side, 



y.C.f. the vena cava inferior; O, the oesophagus; Ao. the aorta j, tLe 

 broad white tendinous middle (B) is easily distinguished from the radiating 

 muscular fibres (A) which pass down to the ribs and into the pillars (C D) in 

 front of the vertebrae. 



