INSPIRATORY MUSCLES. 



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INSPIRATORY MUSCLES. 



The act of inspiration is not performed by any single muscle ; 

 indeed, even the most gentle and quiet respiration requires the 

 coordinated action of many sets of muscles. Most of these mus- 

 cles have other duties to perform besides helping to produce res- 

 piratory movements. 



FIG. 150. 



Diagram of a section made vertically from side to side through the tho- 

 racic and part of the abdominal cavities to show the position of the dia- 

 phragm, which is indicated by the dark line (D D) placed on the parts of 

 the muscle that descend in inspiration. p. Pericardial cavity. L. Liver. 

 s. Stomach. K. Roots of lungs cut through. 



Those which are strictly inspiratory in their function are : 



1. The Diaphragm with its accessory Quadratus Lumborum 



to fix its origin from the last rib. 



2. Levatores costarum (including the scaleni) with their ac- 



cessory intercostals, which act chiefly as regulators. 



3. The Serratus posticus superior. 



tThe Diaphragm is the most important inspiratory muscle. It 

 s the only one muscle which unaided can keep up the necessary 

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