EXPIRA TION. 



173 



room for themselves by pushing out the soft front wall 

 of the abdomen, which therefore protrudes. 



22. The Combined Action of the Diaphragm and of the 

 Muscles which Raise the Rihs is such as to considerably 

 increase the chest-cavity. This is illustrated in Fig. 47. 

 In B are shown the size and form of the thoracic 

 cavity, and the position of the diaphragm, after an expi- 



FIG. 47. Diagrams showing' the form and size of the chest and abdomen during 

 inspiration, A, and expiration, B. C, chest-cavity; D, diaphragm; E, spinal col- 

 umn; F, collar-bone; 6V, sternum; A6, abdomen; G, hip-bone; //, coccyx. 



ration. A represents the chest and diaphragm at the 

 end of an inspiration. 



23. Expiration. In expiration, the chest-cavity is di- 

 minished, and air driven out of the lungs. It is ordina- 

 rily brought about without muscular work. The mus- 



22. What is the result of the combined action of the diaphragm and 

 the. muscles raising the ribs during inspiration ? 



23. What happens during expiration? How is it ordinarily brought 

 about ? Explain ? 



