THE THORAX. 



353 



the two upper : both blending with the anterior common ligament of the spine. 

 These tendinous portions of the crura pass forward and inward, and gradually 

 converge to meet in the middle line, forming an arch, beneath which passes the 

 aorta, vena azygos major, and thoracic duct. From this tendinous arch muscular 

 fibres arise, which diverge, the outermost portion being directed upward and 

 outward to the central tendon ; the innermost decussating in front of the aorta, 

 and then diverging, so as to surround the O3sophagus before ending in the central 

 tendon. The fibres derived from the right crus are the most numerous and pass 

 in front of those derived from the left. 



The Central or Cordiform Tendon of the Diaphragm is a thin but strong 

 tendinous aponeurosis, situated at the centre of the vault formed by the muscle, 



Open 



FIG. 216. The Diaphragm. Under surface. 



immediately below the pericardium, with which it is partly blended. It is shaped 

 somewhat like a trefoil leaf, consisting, of three divisions, or leaflets, separated 

 from one another by slight indentations. The right leaflet is the largest; the 

 middle one, directed toward the ensiform cartilage, the next in size ; and the 

 left, the smallest. In structure, the tendon is composed of several planes of 

 fibres Avhich intersect one another at various angles, and unite into straight or 

 curved bundles an arrangement which affords it additional strength. 



The Openings connected with the Diaphragm are three large and several 

 smaller apertures. The former are the aortic, the oesophageal, and the opening 

 for the vena cava. 



The aortic opening is the lowest and the most posterior of the three large 



apertures connected with this muscle, being at the level of the first lumbar 



vertebra. It is situated slightly to the left of the middle line, immediately in 



front of the bodies of the vertebrae ; and is, therefore, behind the Diaphragm, not 



2:5 



