194 PRACTICAL ANATOMY. 



There are three important openings in the diaphragm: 

 1. The aortic, bounded posteriorly by the bodies of the 

 vertebrae, latterly and anteriorly by the crura, which are 

 continuous along their inner borders, forming a fibrous 

 margin or arch, beneath which passes the aorta. 2. The 

 O2sophageal opening, in front of the aortic, is elliptical in 

 form ; it is made by the decussation of the planes of 

 muscular fibres attached to the crura ; the muscular fibres 

 from the right crus pass to the left ; those from the left 

 cms pass to the right, and two inches in front of this 

 again decussate, making an elliptical opening for the 

 passage of the oesophagus and pneumogastric nerves. 

 This arrangement of decussating fibres makes a sphinc- 

 ter for the lower end of the oesophagus, or cardiac end 

 of stomach. 3. To the right of the cesophageal opening, 

 in the right leaflet of the central tendon, is the quadrate 

 opening for the passage of the ascending vena cava. It 

 is so constructed that traction on the tendon of the 

 diaphragm will enlarge it. The opposite is true of the 

 cesophageal opening. The diaphragm is supplied by the 

 two phrenic nerves from the cervical and brachial plex- 

 uses, arches well into the chest, but approximates a plane 

 when in a state of marked contraction. 



MUSCLES OF THE BACK. 



The muscles of the back are disposed in five layers. 



Muscles of the First Layer. 

 TRAPEZIUS. 



Origin Ligamentum nuchae, superior curved line of 

 occipital bone, spine of seventh cervical vertebra, 

 spines of all dorsal vertebrae. 

 Insertion Into upper border of spine of scapula 



outer one-third of posterior border of clavicle. 

 Nerve Spinal accessory. 



