RESPIRATION 193 



it in any way, as, for example, by placing a heavy 

 poultice on the front of the chest. 



The elevation of the ribs is effected partly by the 

 scaleni and intercostals, partly by the diaphragm. The 

 normal condition of the latter is one of * arched tension,' 

 it being held up partly by its attachment to the peri- 

 cardium, partly by the pull exercised on it by the 

 elasticity of the lungs. It is the tension of the 

 diaphragm, indeed, which retains in the lungs their 

 supplemental air. As long as the ribs are fixed the 

 diaphragm cannot be pushed upwards, but if the 

 abdominal muscles pull the lower ribs inwards, then 

 the tension of the diaphragm is relaxed, and the 

 abdominal viscera, under the pressure of the abdominal 

 muscles, can drive it upwards and expel the supple- 

 mental air. 



The mode of action of the diaphragm is peculiar, and 

 has important bearings in disease.* The diaphragm is 

 to be regarded as a digastric muscle which takes origin 

 from the vertebrae behind, and is inserted into the lower 

 six ribs. Its central tendon rests upon the liver, which 

 acts as a sort of fulcrum, over which the muscle passes. 

 As the diaphragm contracts, the liver tends to be pushed 

 forwards and downwards ; but its movement in this 

 direction is frustrated by the anterior abdominal wall, 

 with the consequence that it forms a fixed point, over 

 which the ribs are pulled up. If the abdominal muscles 

 are badly developed, however, or if they have become 

 partially atrophied from practical disuse, as happens, 



* Keith, 'The Anatomy of Glenard's Disease,' London Hasp. 

 Gaz., 1902, ix. 55. 



13 



