THE ABDOMEN 



759 



diameter of each half of the thorax. .The diaphragm also elevates 

 the lower ribs, except the last. 



Metastemum 



Stemal Origin 



Central Tendon 



Caval Opening 



CEsophageal 

 Opening 



Ltgamentum Arcuatum •'' 

 Externum 



Quadratus Lumborum ^ 



Ligamentum Arcuatum Internum ' 



Psoas Magnus 



Right Cms Intervertebral Disc 



Fig. 325. — The Diaphragm (Inferior View). 



The muscular fibres pass in an arched manner upwards and inwards to the 

 central tendon, upon which they converge from all points. The stemal 

 portion is separated on either side from the costal portion by a small interval 

 occupied by areolar tissue, through which the superior epigastric vessels and 

 some of the superficial lymphatics of the upper surface of the liver pass. 

 Above and below this interval are the pleura and peritoneum respectively. 

 In this situation a diaphragmatic hernia may take place, involving one or 

 other of the abdominal viscera. Between the lowest costal fibres and the 

 corresponding external arcuate ligament there is sometimes another areolar 

 interval of small size. The crura are strong, thick musculo-tendinous 

 bundles disposed verticallj', the left being the smaller, shorter, and more 

 posterior of the two. Each crus is fleshy externally, and strongly tendinous 

 internally, the lower extremity of each being entirely tendinous. On a level 

 with the lower border of the body of the twelfth thoracic vertebra the inner 

 tendinous fibres of the crura are connected by a fibrous band, called the 

 middle arcuate ligament, which lies in front of the aorta. The muscular 

 fibres of the crura pass upwards in a diverging manner to be inserted into the 

 posterior border of the central tendon. The innermost muscular fibres on 

 either side, reinforced by fibres springing from the middle arcuate ligament, 

 decussate before reaching the central tendon and enclose between them the 

 oesophageal opening. In the decussation the bundle derived from the right 

 crus passes in front of th t from the left, which latter is of small size. 



The central tendon is also called the cordiform or trefoil tendon. 

 It is much elongated from side to side, convex in front, and con- 



