HUMAN PHYSIOLOGY 



CHAP. 



much larger round your chest is after you breathe in 

 (inhale) than after you breathe out (exhale). Now 

 measure once more after you have inhaled all you can 

 hold, and again after you have forced out all you can 

 possibly exhale. 



i 



...10 



u 



FIG. 21. Showing the heart and lungs in position in the thorax. (From 

 Huxley's " Elementary Physiology "): 1-12, ribs; s, breast bone ; c, c, car- 

 tilages of ribs ; c, collar bone ; /, lungs ; a, apex of heart ; peric, pericar- 

 dium, inclosing the heart. 



Every time the chest enlarges, air is pushed in 

 through the air passages to keep the lungs full. When 

 the muscles relax, the chest grows smaller, the lungs 



