130 Mr. Le Gros Clark on the Mechanism of Respiration. 



not entirely, correspond with that of the elevation of the anterior attach- 

 ment of the rib ; so that the pectoral fibres will not be appreciably shortened, 

 and consequently cannot materially assist in the inspiratory effort. If we 

 ascend a step higher, to the fifth rib, it would appear that tbe pectoral 

 fibres will rather resist than assist in the act of inspiration ; still more is 

 this the case nearer to the clavicle. 



Fig. 2. 



When the arms are raised above the head, the great pectoral muscles 

 would have an undoubted action in elevating the ribs ; but such a position is 

 never assumed, even in disease, for the purpose of assisting inspiration. 



19. Indeed the same may be said of the serratus magnus and pectorales 

 as of the intercostals and other muscles credited with agency in respiration, — 

 that their action must be studied in relation to that of other muscles, which 

 have an important influence in modifying or even in determining their 

 action ; and bearing this in mind, and for the reasons adduced, I think it 

 very questionable whether any of these muscles can exercise an influence, 

 except under special conditions and to a very limited extent, in the act of 

 inspiration. 



20. The conclusion to which the foregoing observations point is, that 

 the act of inspiration is, under all circumstances, essentially, perhaps 

 exclusively, dependent on the special muscles appropriated to this function — 

 muscles which are competent, without extraneous aid, to answer the appeal 

 made to them in emergencies as well as under ordinary circumstances. 



21. The action of the scalenus anticus, a powerful muscle, is essential 



