54 PHYSIOLOGY FOR THE LABORATORY. 



muscles. The band 3-4, running obliquely downward and 

 backward, represents the internal intercostal muscles. 



a. Stretch a band over the hooks 1-2. What change is 

 there in the position of the horizontal pieces of cardboard ? 

 What effect does the contraction of the external intercostal 

 muscles have on the ribs and on the chest cavity ? 



b. Remove the band from hooks 12 and stretch it over 

 hooks 3-4. What change is there in the position of the 

 pieces of cardboard? What is the effect of the contrac- 

 tion of the internal intercostal muscles? 



III. THE LATERAL ENLARGEMENT OF THE THORAX. 



In the body the ribs are curved, instead of being straight 

 as represented in Fig. 8, and as they rise during inspiration, 

 they also bulge outward, thus increasing at the same time 

 the lateral dimension of the chest cavity. 



