A<TTOX OF THE DIAPHRAGM. 361 



is only a thickened piece of the fascia covering that muscle, and 

 extends from the first lumbar transverse process to the last rib. 



AI :/-/"/vx. There are three large openings ; one each for the aorta, Apertures 

 the vena cavn, and the oesophagus ; with some smaller fissures for ar 

 nerves and vessels. 



The opening for the aorta (k) is rather behind than in the diaphragm, For the 

 for it is situate between the pillars of the muscle and the spinal ac 

 column : it transmits the aorta, the thoracic duct, and the large 

 azygos vein. 



The opening for the oesophagus and the pneumo-gastrie nerves (i) For gullet 

 is above and slightly to the left of the aortic aperture : it is placed aD 

 in the muscular part of the diaphragm, and is bounded by the fibres 

 of the pillars as above explained. 



The opening for the vena cava (foramen quadratum ; h) is situate 

 between the middle and right divisions of the central tendon ; and 

 its margins are attached to the vein by tendinous fibres. 



There is & fissure (j) in each pillar for the three splanchnic nerves ; Fissures in 

 and through that in the left cms the small azygos vein also passes. 



Action of the diaphragm. By the contraction of the muscular fibres 

 in inspiration the tendon, particularly its lateral parts, is moved 

 downwards, and the arch of the diaphragm lessened. During relaxa- 

 tion in expiration, the centre of the muscle is elevated, and the 

 height of the vault increased owing to the elasticity of the lungs, and 

 the pressure of the viscera below, which are forced upwards by the 

 action of the abdominal muscles. In forced expiration the muscle Hei |^ t in 

 reaches as high as the fourth rib on the right side, and the fifth on expiration. 

 the left, close to the sternum. 



In the descent of the diaphragm, the parts of the tendon move Central part 

 unequally, in consequence of differences in their relations, and in least ; 

 the length and direction of the fleshy fibres connected with them. 

 Thus, the central lobe, above which the heart is placed, moves least ; 

 while the lateral lobes, which are below the lungs descend more 

 freely. It is estimated that the central lobe of the tendon moves left part 

 downwards in full inspiration about two-fifths of an inch, the right 



lobe twice as much, and the left lobe one inch. (Hasse). fufun? i 



Keith is of opinion that an important part of the action of the tion. 

 crura, the fibres of which pass into the central part of the tendon, 

 is to render tense, and depress the attached fibrous pericardium, 

 and to exercise a pull upon the aorta of the lungs, which are held to 

 the upper surface of the tendon of the diaphragm by the broad 

 ligament of the lung. 



With the movement of the diaphragm the size of the cavities of Effect on 

 the abdomen and thorax are altered. By its descent the thorax abd^me^ 

 is enlarged and the abdomen diminished ; and the viscera in the on viscera, 

 upper part of the latter cavity, viz., liver, stomach and spleen, are 

 partly moved from beneath the ribs. By its ascent the cavity of 

 the thorax is lessened, and that of the abdomen is restored to its 

 former size ; and the displaced viscera return to their usual place. and on 

 By the contraction of the fibres the aperture for the oesophagus will apertures. 



