254 



RESPIRATION 



every muscle is brought into play which by its contraction tends to elevate 

 the ribs and sternum or which will fix points against which these muscles 

 can act. This includes almost every muscle of the trunk and neck. 



Changes in the vertical diameter are due, first, to the contraction of the 

 diaphragm. This muscle has the shape of a flattened dome, its highest 



Esophagus 



Left subclavian artery 

 Left common carotid artery 

 Left superior intercostal vein 

 Left innominate vein 



Parietal pleura 

 (cut edge) 



Pericardium 



Parietal pleura 

 (cut edge) 



Aortic arch 



Pulmonary artery 

 Bronchus 



Pulmonary veins 

 Esophagus 



Diaphragm 



FIG. 229. Thorax from the Left, Showing Left Pleural Sac, and the Diaphragm. The lung is 



removed. 



point being the central tendon. While passive, its lower portions are in 

 apposition with the chest walls, figure 228, 7. On contraction, the dome is 

 pulled downward and the lower portion is pulled away from the chest walls, 

 the downward displacement varying from 6 to 12 mm. in normal respira- 

 tion, and in forced respiration may amount to as much as 45 mm. The 

 tendency of the diaphragm to pull the lower ribs and lower part of the sternum 



