RESPIRATORY MUSCLES. 



335 



Diagram showing interval be- 

 tween the position of the dia- 

 phragm in expiration (e, e) and 

 inspiration (i, t). The increase 

 in capacity is shown by the white 

 areas. 



tion is aided by the abduction of the FIG. 151. 



floating ribs, which is accomplished by 

 the quadratic lumborum and the deep 

 dorsal muscles. 



In order that the diaphragm may 

 act to the best advantage, it is neces- 

 sary that its attachments be fixed by 

 the other muscles ; for when the quad- 

 ratus lumborum, levatores, and other 

 fixing muscles are not acting, the lower 

 floating ribs are drawn in by the dia- 

 phragm, and the power of that muscle 

 is much diminished by the approxima- 

 tion of its attachments. This may be 

 seen in spinal injuries when the respi- 

 ration is carried on by the diaphragm 



alone. In these cases a circular furrow marks the line of attach- 

 ment of the muscle to the lower ribs and their cartilages, which 

 are drawn inward during each inspiration, the breathing being, 

 of course, purely abdominal in type. 



The Quadratus Lumborum, which passes from the pelvis to the 

 last rib, has, besides the action in aid of the diaphragm just men- 

 tioned, the power of drawing down the lower outlet of the thorax, 

 iii which it is helped by other abdominal and dorsal muscles. In 

 this action it may be regarded as the antagonist of the next 

 group. 



The Scaleni Muscles, which pass down from the lateral aspects 

 of the cervical vertebrae to the first two ribs, which they raise so 

 as to draw up the upper outlet of the thorax. The quadratus 

 and scaleni muscles thus act upon the thorax in the same way as 

 the hands when extending a concertina. 



The Levatores Costarum are small muscles, but on account of 

 their number, their aggregate force is much greater than is com- 

 monly thought. They are short, thick muscles, which pass ob- 

 liquely downward and outward from the transverse processes of 

 the dorsal vertebrae to the angle of the ribs. Their only action 

 is to raise the angle of the ribs, and thus diminish their anterior 



