THE DIAPHRAGM. 553 



right cms is the larger of the two and arises tendinous from 

 the sides and anterior surface of the four upper lumbar ver- 

 tebraB and their intervertebral ligaments; the left crus, being 

 the smaller, comes from the two upper vertebra}. Both crura 

 ascend and are connected upon the last dorsal vertebra by 

 a tendinous cord, semilunar in shape, which arches over the 

 aorta and thoracic duct. A little above this point the crura 

 approach each other and decussate, and pass on to be in- 

 serted into the notch and posterior margin of the central 

 cordiform tendon. The greater and lesser muscles of the 

 diaphragm have their attachments completed by the liga- 

 mentum arcuatum, which extends from the transverse pro- 

 cess of the first lumbar vertebra, and body of the second, to 

 the twelfth rib. To the upper margin of this tendon the 

 diaphragm is attached, and to its lower margin the psoas 

 magnus muscle, and under it is placed the sympathetic 

 nerve. The diaphragm contains three large openings ; one, 

 for the aorta, thoracic duct, and great splanchnic nerves, is 

 a long elliptical foramen, situated between and behind the 

 crura, and in front of the bodies of the last dorsal and three 

 upper lumbar vertebra?. The second opening is about three 

 inches above and to the left of the aortic. Its form is that 

 of a long oval, situated in the posterior part of the muscle, 

 between the spine and notch of the tendon, the decussa- 

 ting fasciculi forming its parietes and separating it from 

 the aortic. The oesophagus and eighth pair of nerves pass 

 through this foramen. The third opening is for the vena 

 cava ascendens. It is a large foramen a little higher than 

 the oesophageal, situated to the right and in the back part 

 of the cordiform tendon. It is something of a quadrilateral 

 figure, having its margins tendinous all round, with fasci- 

 culi passing upon the vein above and below, and thus afford- 

 ing an arrangement by which it is kept constantly open, 

 and all interruption to the circulation prevented. 



The blood-vessels of the diaphragm are the phrenic, the 

 first branches of the aorta after entering the abdomen, the 

 internal mammary, intercostals, and branches from the re- 

 nal and lumbar arteries. The veins open either into the 



