ACTION OF THE SCALENI. 373 



thorax, from the mode of articulation and direction of the 

 ribs, which are somewhat rotated as well as rendered more 

 horizontal. 



Perhaps there is no set of muscular actions to which as 

 much observation and speculation have been devoted as those 

 concerned in respiration ; and the actions of the muscles 

 which are attached to the thorax are so complex and difficult 

 of observation that the views of physiologists concerning 

 them are still somewhat conflicting. "While some adopt the 

 opinion of Haller, 1 that the first rib is almost fixed and im- 

 movable, others contend, as did Magendie, that it is the 

 most movable of all. 2 With regard to this point there can 

 now, it seems, be no doubt. By putting the thumb and fin- 

 ger on either side of the neck over the scaleni, we can dis- 

 tinctly feel these muscles contract with every tolerably deep 

 inspiration (a movement which Magendie proposed to call 

 the respiratory pulse, loo. cit.) ; and it is further evident 

 that though in the male, in ordinary respiration, the sternum 

 is almost motionless, in the female, and in the male in deep 

 inspirations, the sternum is considerably elevated and pro- 

 jected, particularly at its lower part. This latter movement 

 increases the antero-posterior diameter of the thorax, and can 

 be measured with an appropriate instrument. The elevation 

 of the sternum is necessitated by its close and almost im- 

 movable connection, through its short cartilage, with the 

 first rib. 



The action of the scaleni, while it is inconsiderable in 

 ordinary respiration in the male, in all cases renders the first 

 rib practically a fixed point, from which those intercostal 

 muscles which raise the ribs can act. 



Intercostal Muscles. Concerning the mechanism of the 

 action of these muscles, there is great difference of opinion 

 among physiologists ; so much, indeed, that the author of a 



1 Elementa Physiologies, Lausanne, 1761, tomus iii., p. 23. 

 3 Precis filetnentaire de Physiologic, tome ii., p. 317. 



