422 



THE MUSCLES AND FASCIA 



The oesophageal opening (hiatus oesophageus) is situated at the level of the tenth 

 thoracic vertebra; it is elliptical in form, oblique in direction, muscular in structure, 

 and is formed by the decussating fibres of the two crura. It is placed above, and 

 at the same time anterior, and a little to the left of the aortic opening. It transmits 

 the oesophagus and vagus nerves and some small oesophageal arteries. The 

 anterior margin of this aperture is occasionally tendinous, being formed by the 

 margin of the central tendon. The posterior and lateral margins are thick and 

 the gullet is in contact with them for about half an inch. The right margin of the 

 oesophageal opening is particularly prominent and lies in the oesophageal groove 

 on the posterior surface of the left lobe of the liver. 



The opening for the inferior vena cava '(foramen venae cavae) is the highest open- 

 ing, being about on the level of the disk between the eighth and ninth thoracic 

 vertebras; it is quadrilateral in form, tendinous in structure, and is placed at the 

 junction of the right and middle leaflets of the central tendon, its margins being 

 adherent to the wall of the inferior vena cava. 



FIG. 317. The Diaphragm, viewed from below. (Testut.) 



The right crus transmits the greater and lesser splanchnic nerves of the right 

 side; the left crus transmits the greater and lesser splanchnic nerves of the left 

 side, and the vena azygos minor (inferior). The gangliated cords of the sympa- 

 thetic usually enter the abdominal cavity by passing behind the internal arcuate 

 ligaments. 



Serous Membranes. The serous membranes in relation with the Diaphragm are four in 

 number, three covering its upper or thoracic surface, and one its abdominal surface. The three 

 serous membranes on its upper surface are the two pleurae on either side and the pericardium, 

 which covers the middle portion of the tendinous centre. The greater portion of the under 

 surface of the Diaphragm is covered by the peritoneum. 



Nerves. The Diaphragm is supplied by the right and left phrenic nerves, derived from the 

 anterior primary divisions of the third, fourth, and fifth cervical nerves. The nerve filaments 

 which pass to the Diaphragm from the lower four intercostal nerves are sensor in function and 

 supply only the peritoneum. 



Actions. Each External intercostal muscle elevates the rib below. Owing to the oblique 

 axis of the costovertebral articulation, the curved obliquity of the ribs themselves, and the 



