164 



RESPIRATION. 



greater diversity than naturally exists in the modes of in- 

 spiration. 



From the enlargement produced in inspiration, the chest 

 and lungs return in ordinary tranquil expiration, by their elas- 

 ticity ; the force employed by the inspiratory muscles in dis- 



FlG. 64. 



FIG. 63 (after Hutchinson). The changes of the thoracic and abdominal walls of 

 the male during respiration. The back is supposed to be fixed in order to throw for- 

 ward the respiratory movement as much as possible. The outer black continuous 

 line in front represents the, ordinary breathing movement ; the anterior margin of 

 it being the boundary of inspiration, the posterior margin the limit of expiration. 

 The line is thicker over the abdomen^-eince the ordinary respiratory movement is 

 chiefly abdominal : thin over the chest, for there is less movement over that region. 

 The dotted line indicates the movement on deep inspiration, during which the ster- 

 num advances while the abdomen recedes. 



FIG. 64 (after Hutchinson). The respiratory movement in the female. The lines 

 indicate the same changes as in the last figure. The thickness of the continuous line 

 over the sternum shows the larger extent of the ordinary breathing movement over 

 that region in the female than in the male. 



tending the chest and overcoming the elastic resistance of the 

 lungs and chest-walls, being returned as an expiratory effort 

 when the muscles are relaxed. This elastic recoil of the rib- 

 cartilages, but also of the lungs themselves, in consequence of 

 the elastic tissue which they contain in considerable quantity, 

 is sufficient, in ordinary quiet breathing, to expel air from the 

 chest in the intervals of inspiration, and no muscular power 



