RESPIRATION IN MAN 183 



and their musculature as an individual part of the respiratory 

 mechanism. 



(11) The diaphragm acts as a true piston, moving the abdominal 

 contents downwards and forwards, the direction depending on the 

 type of respiration. The effect of its contraction depends on the 

 action of its antagonists. 



(12) That in describing the movements of the ribs it is neces- 

 sary to recognise at least two types, one representative of the 

 upper costal mechanism and the other of the lower or diaphrag- 

 matic mechanism. The movements of the lower set are correlated 

 with the action of the diaphragm ; those of the upper set work 

 independently of the diaphragm. 



(13) The floating ribs (eleventh, twelfth, and often the tenth) are 

 functionally parts of the abdominal wall. 



(14) The articulations, muscles, movements, and conforma- 

 tion of the ribs of the lower set differ widely from those of the 

 upper set. 



(15) The action of the intercostal muscles depends on the 

 antagonists brought into use. Some intercostal spaces are 

 widened and some diminished during inspiration, and the same 

 is true during expiration. 



(16) The levatores costaram have no action on the ribs ; they 

 are purely spinal muscles. 



In this article the writer proposes to summarise certain recent 

 papers dealing with the respiratory expansion and contraction of 

 the human lungs. The evidence contained in these papers is 

 derived from three sources : (1) From measurements of the res- 

 piratory movements of the body wall by photography, by X-rays, 

 by recording tambours, by direct measurements, or by tracings 

 taken with strips of lead moulded on the body. When possible the 

 writer has selected those observations which deal with the normal 

 unconscious respiratory movements rather than records made on 

 conscious subjects taking exaggerated breaths. (2) From observa- 

 tions on the anatomy of parts concerned in respiratory move- 

 ments, for whatever theory be adopted of these movements, it 

 must give a rational and complete explanation of the form and 

 arrangement of the structures concerned in them. (3) From clinical 

 observations made by means of percussion and auscultation. When 

 the evidence from these three sources is summarised it is found 



