INTERCOSTAL MUSCLES 



97 



Inspiration, caused by the elevation of the ribs and depression 

 of the diaphragm. 



The intercostal muscles fill up the spaces between the ad- 

 jacent ribs. They are arranged in two sets, external and internal, 

 eleven pairs of each. 



Expiration, caused by the slackening of the muscles, the 

 weight of the thorax, and the elasticity of the lungs. The 

 triangularis sterni is a special depressor of the ribs, and some 

 anatomists consider the internal intercostal muscles to be so 

 also. 



Internal Mammary 

 Artery 



External Intercostal Muscle 



Interchondral Part 



cf Internal 

 Intercostal Muscle 



External Intercostal Muscle 



Interosseous Part of Internal 

 Intercostal Muscle 



FIG. 37. INTERCOSTAL MUSCLES. 



