68 ANATOMY AND PHYSIOLOGY FOR NURSES 



that the action of these muscles should be studied closely, 

 making frequent reference to the illustrations. 



Muscles of the Thorax. The muscles of the thorax 

 are the external and internal intercostals , the infracos- 

 tales, the triangularis sterni, and the levator costarum; 

 of these, the most important are the intercostals. They 

 are all connected with the bony structure of the thorax, 

 and are all concerned in respiration. 



FIG. 36. The diaphragm, inferior surface: i, 2, 3, Central cordiform 

 tendon; 4, 5, crura ; 6, internal arcuate ligament; 7, external arcuate liga- 

 ment ; 8, aortic opening; 9, esophageal ; 10, opening for vena cava (Leidy). 



Diaphragmatic Region. The diaphragm is a thin, 

 musculofibrous septum, separating the thorax from the 

 abdominal cavity. It is divided into two parts a greater 

 and a lesser portion. It is convex toward the chest; its 

 circumference is connected with the ribs and the vertebrae. 

 It contains openings for the transmission of the aorta, 

 esophagus, vena cava, nerves, arteries, and veins. Action, 

 a muscle of respiration. 



