306 RESPIRATION. 



without any misgiving as to the infliction of suffering, by re- 

 moving the integument and superficial layer of muscles so as 

 to expose the ribs and intercostal spaces. 



The first lesson to be learnt relates to normal breathing. It 

 it seen that so long as air enters the chest freel} r , and the res- 

 piratory apparatus is not interfered with, there is no appreci- 

 able expansive movement of the ribs, and the intercostal mus- 

 cles, in so far as they are visible, do not contract. Dyspnoea 

 may now be produced, either by letting air into one or both of 

 the~ pleural cavities, by diminishing the opening by which the 

 chest communicates with the atmosphere, or by combining the 

 two methods. It is most convenient to begin with puncturing 

 one pleura. 



The effect of this operation is to increase the respiratory 

 movements, and to alter their character by bringing the tho- 

 racic muscles into action. The upper ribs, particularly the 

 second, third, and fourth, which were before motionless, move 

 upwards and outwards in each inspiration, while the external 

 intercostal muscles, and the intercartilaginous parts of the in- 

 ternal intercostal, are seen to grow hard in contraction at the 

 same moment. 



To produce a higher degree of dyspnoea, the other pleura 

 may be opened; the principal effect observed is that the upward 

 and outward movement of the upper ribs is increased, and that 

 the scaleni, which were before inactive, now begin to contract 

 in concert with the external intercostals. These muscles, 

 although from their anatomical arrangement they must act as 

 elevators of the ribs, cannot be shown to be so experimentally ; 

 for there is no appreciable diminution of the costal movement 

 when they are divided. 



The function of the external intercostals and intercartilagi- 

 nous muscles, having been proved by direct observation in the 

 manner above described, at a very early period in the history 

 of physiology, has never been seriously disputed. This is not 

 however the case as regards the interosseous part of th.e internal 

 intercostals that part of those muscles which is covered by the 

 external intercostals. In the rabbit, the interosseous intercos- 

 tals differ from the intercartilaginous, both in being less oblique 

 and in being somewhat thinner. The experimental evidence 

 as to their function is negative that is to say, it can be shown 

 tha 4 they do not contract with the external muscles, but it 

 cannot be shown that they act antagonistically to them. It 

 admits of demonstration as regards any of the lower ribs, from 

 the fourth to the eighth or ninth, that if all the muscles at- 

 tached to it from above are removed, excepting the external 

 intercostals and the levatores costarum breves (muscles which 

 connect each transverse process with the rib next below it, and 

 can be seen to contract with the external intercostals), the rib 



