282 RESPIRATORY MOVEMENTS OF MAMMALS. 



movement of the diaphragm ; and in the second, by that of 

 the ribs. 



331. i. The diaphragm, in a state of rest or relaxation, 

 forms a high arch, which rises into the interior of the chest, 

 as at <7, fig. 163 ; but when it contracts, it becomes much 

 natter (though always retaining some degree of convexity 

 upwards), and thus adds considerably to the capacity of the 

 lower part of the chest. The under side of the diaphragm is 

 in contact with the liver and stomach, which, to a certain 



c a h 



Fig. 163. THORAX OP MAN. 



degree, rise and fall with it. It is obvious that, when the 

 diaphragm descends, these organs, with the abdominal viscera 

 in general, must be pushed downwards ; and as there can be 

 no yielding in that direction, the abdomen is made to bulge 

 forwards when the breath is drawn-in. On the other hand, 

 when the contraction of the diaphragm ceases, the abdominal 

 muscles press back the contents of the abdomen, force up the 



