98 ANATOMY AND PHYSIOLOGY 



separating the abdominal and thoracic cavities. The central 

 portion is aponeurotic, serving for the insertion of the remaining 

 or muscular portion. 



Origin. i. By two vertical bundles at the sides of the lumbar 

 vertebrae. These vertical portions are the crura of the diaphragm. 

 Their fibers turn forward, crossing and interlacing before they end 

 in the central tendon. 2. From arches of lumbar fascia and the 

 lower boundary of the thorax (seventh to twelfth ribs and xiphoid 

 appendix) . 



Insertion. In a flat central tendon, shaped like a clover leaf, 

 near the center of the dome. The lateral portion of the muscle arch 

 is higher than the central, forming a cupola on each side. 



FIG. 82. THE DIAPHRAGM, INFERIOR SURFACE. 



e i, 2, 3, Tendinous leaflets; 4, muscle fibers; 5, 6, 7, tendinous arches; 8, 10, fibers 

 arising from vertebrae; n, aorta a large artery; 12, esophagus, leading to stomach; 

 13, opening for vena cava. (Potter's Compe'nd of Anatomy.} 



Action. When the diaphragm contracts it becomes flattened, 

 pressing upon the abdominal organs; when it relaxes, it springs 

 back to its dome-shape, as high as the fourth or fifth rib, pushing 

 gently against the lungs. (See p. 121.) 



Nerve. Phrenic and lower intercostal. 



Special points. This muscle ^forms the floor of the thorax, and 

 at the same time the roof of the abdomen (convex floor, concave 

 roof). There are three openings in it at the back part for the 



