202 



RESPIRATION. 



" At the base of the thorax, the diaphragm s is subtended 

 in the form of an arch." The central part is tendinous, and has 

 an irregularly quadrilateral opening rather to the right, for the 

 transmission of the vena cava, which adheres to its margin 

 and is thus kept open. From this tendinous centre, muscular 

 fibres proceed in all directions, and the anterior and lateral are 

 inserted into the ensiform cartilage and six lowest ribs and 

 their cartilages, while the posterior fibres converge into two 

 great bands, called pillars of the diaphragm, which run down- 

 wards and are inserted by means of two tendons into the three 

 first lumbar vertebrae. At their origin they leave an oval 

 opening between them for the passage of the oesophagus and 

 pneumo-gastric nerves, each bunch sending a bundle across to 

 the other in order to complete the opening behind. More pos- 

 teriorly, near their termination in tendon, they leave a para- 

 bolic opening for the aorta, vena azygos, and thoracic duct. 



a, central tendon. 



4, surrounding muscle. 



c, crura. 



d, tendons of crura. 



e, opening for vena cava. 



f, opening for oesophagus. 



g, space for aorta. 

 h, ossa ////. 



When the fibres contract, the diaphragm descends, chiefly at 

 its sides, and ceases to be vaulted, and the cavity of the chest 

 lengthens. It is the lateral portions only which in ordinary in- 

 spiration sensibly descend. 



8 " Haller, Icon. Anat. fascic. 1. tab. i. 



B. S. Albinus, Tab. muscuhr. tab. xiv. fig. 5, 6, 7. 



J. G. Rbderer, De arcubus tendineis muscul. progr. 1. Getting. 1760. 4to. 



Santorini, Tab. Posth. x. fig. 1." 



