THE CHEST. 99 



phragm, a somewhat fan-shaped muscle that forms the 

 floor of the chest cavity. It takes its origin from the 

 ensiform cartilage, the six or seven lower ribs and their 

 cartilages, and from the upper three or four lumbar 

 vertebrae, that is, from the whole of the internal circum- 

 ference of the thorax, and is inserted into the central 

 cordiform tendon. It has several large and several 

 small openings for the aorta, the esophagus, the venae 

 cavse, the thoracic duct, and various nerves, and its 



FIG. 38. Interior view of the diaphragm. (Leidy.) 1-3, The three lobes 

 of the central tendon, surrounded by the fleshy fasciculi derived from the inferior 

 margin of the thorax; 4, 5, the crura; 6, 7, the arcuate ligaments; 8, aortic orifice; 

 9, esophageal orifice; 10, quadrate foramen; 11, psoas muscle; 12, quadrate 

 lumbar muscle. 



surfaces are covered by serous membranes, by the two 

 pleurae and the pericardium above and by the peritoneum 

 below. It partially supports the heart and lungs. Con- 

 vex toward the chest, it becomes flattened in contraction 

 and so increases the capacity of the chest. It aids in all 

 expulsive acts, as sneezing, coughing, laughing, urinat- 

 ing, defecating, vomiting, and childbirth. Hiccough is 

 spasm of the diaphragm. 



The arteries of the chest are the intercostal branches 



