214 



MUSCLES OF THE TRUNK AND CHEST. 



crura ; between which an interval is left for a transit of the 

 aorta {Fig 2\ . 5), the vena azygos, the thoracic duct, and 

 sympathetic nerve. Between the two, and rather to the left 

 and centre, is situated a third opening, formed by the decus- 

 sation of the fibres of the crura, through which pass the 

 oesophagus and the par vagum nerve {Fig 21 . 6) . 



FIG 21. 



THE DIAPHRAGM. 



1, 1, 1, The cordiform, or tendinous 



portion. 



2, 2, 2, Tlie great muscle. 



3, The left crus. 



4, The right crus. 



5, The aorta, piercing the left or 



superior opening. 



6, The oesophagus, coming through 



the middle opening. 



7, The inferior, or right foramen, 



for the vena cava to pass 

 through. 



8, The sacro-lumbalis muscle. 



Vessels and nerves of the diaphragm. — The aorta, in its 

 passage between the crura, gives a branch or tw^o to this 

 muscle; besides which, it receives other rami from the 

 arteries of the ribs and the pectorals. Its veins, or sinuses, 

 are much larger than its arteries ; to obviate the effects 

 of pressure during its motions, being formed flat without 

 valves ; and finally pour their contents into the vena 

 cava, being the last veins that empty into that trunk. 

 The phrenic nerves arise from filaments given from the 

 fourth, fifth, sixth, and seventh cervicals : other small 

 branches are likewise given off from the surrounding gan- 

 glia, which, uniting with it, tend to make it an organ of 



