98 RESPIRATION 



The opening for the oesophagus is surrounded with muscular fibres, 

 by which it is partly closed when the diaphragm contracts in inspiration, 

 as the fibres simply surround the tube and are not attached to its walls. 



The opening for the aorta is bounded by the bone and aponeurosis 

 posteriorly, and in front, by a fibrous band to which the muscular fibres 

 are attached, so that their contraction has a tendency rather to increase 

 than to diminish the calibre of the vessel. 



The opening for the vena cava is surrounded by tendinous structure, 

 and contraction of the diaphragm, although it may render the form of 

 the opening more nearly circular, can have no effect on its size. 



13 



20 



Fi g- 33- Diaphragm (Sappey). 



I, 2, 3, central tendon; 4, right pillar; 5, left pillar; 6, 7, processes between the pillars; 8, 8, 

 openings for the splanchnic nerves ; 9, fibrous arch passing over the psoas magnus ; 10, fibrous arch 

 passing over the quadratus lumborum ; n, muscular fibres arising from these two arches ; 12, 12, mus- 

 cular fibres arising from the lower six ribs ; 13, fibres from the ensiform cartilage ; 14, opening for the 

 vena cava ; 15, opening for the oesophagus ; 16, opening for the aorta ; 17, 17, part of the transversalis 

 muscle; 18, 18, aponeurosis; 19, 19, quadratus lumborum; 20, 20, psoas magnus; 21, fourth lumbar 

 vertebra. 



In ordinary inspiration, the descent of the diaphragm and its ap- 

 proximation to a plane are the chief phenomena observed ; but as there 

 is some resistance to the depression of the central tendon, it is probable 

 that there is also a slight elevation of the inferior ribs. 



The phenomena referable to the abdomen which coincide with the 

 descent of the diaphragm can easily be observed in the human subject. 

 As the diaphragm is depressed, it necessarily pushes the viscera before 

 it, and inspiration is therefore accompanied with protrusion of the 

 abdomen. 



