Chap, ii.] fbe Diaphragm* 159 



mis, and is inferted into the lower edge of the cartikges 

 of the third, fourth, and fifth ribs. Its effedt is to de- 

 prefs thefe cartilages and the extremities of the ribs, 

 to contract the cavity of the thorax, and therefore to 

 afiifl in expiration. 



The moft important mufcle of the thorax, however, 

 Hill remains to be confidered. The diaphragm is a 

 broad and ftrong mufcle, which divides the cavity of 

 the abdomen from that of the thorax. It is placed 

 very obliquely between thefe two cavities, its anterior 

 connection being much higher than its pofterior. Its 

 middle part is forced up by the vifcera of the abdomen, 

 fo as to form an arch. The diaphragm, at its anterior 

 part, arifes from the upper and internal part of the 

 cnfiform cartilage, and from the cartilages of the fixth, 

 feventh, and all the inferior ribs. The mufcular por- 

 tions arifing from all thefe points converge towards a 

 common center, where they terminate in a broad trian- 

 gular tendon. This being directed downwards and 

 backwards is attached to a mufcular fubflance, which 

 arifes by eight heads from the fecond, third, and fourtii 

 lumbar vertebrae. There are feveral pafTages through 

 the diaphragm, which muft not be pafled over in filence. 

 Among the mufcular portion? which proceed frum the 

 lumbar vertebras, are openings through which pafs the 

 aorta, the thoracic duel:, the vena azygos, and the 

 two great intercoftal nerves. The mufcular fibres, 

 which proceed from the lumbar vertebrae, run ob- 

 liquely upwards and forwards, and form in the 

 middle two flefhy columns, which decuflate, and leave 

 an oval fpace between them for the paflage of the 

 cefophagus and eighth pair of nerves. Towards the 

 right fide of the broad tendon, which forms the middle 

 of the diaphragm, there is a large quadrangular open- 

 ing, through which the vena cava pafles to arrive at 



the 



