RESPIRATION 109 



the external intercostal muscles are arranged obliquely between the ribs in 

 such a way that when the fibers shorten the ribs are drawn closer together. 

 Thus, all except the top ribs are raised, as the accompanying diagram 



FIG. 61 



Anterior view of the thorax. 

 FIG. 62 



Diaphragm as seen from below: 1, 2, 3, the three lobes of the central tendon connecting the 

 muscular fasciculi extending from the lower edge of the thorax, the crura (4, 5), and the arcuate 

 ligaments (6, 7); 8, aorta; 9, esophagus; 10, quadrate foramen; 11, psoas muscle; 12, quad- 

 ratus lumborum muscle. The convexity is upward. 



makes plain. The muscles which aid these intercostals are the levatores 

 costarum, the scaleni, and the serrati postici. The quadratus lumborum 

 connects the pelvis with the last rib, and by its tonic resistance holds the 



