ACTION OF THE INDIVIDUAL RESPIRATORY MUSCLES. 215 



spiration. (d) If, on a preparation of the chest, the ribs be elevated, 

 with widening of the intercostal spaces, as occurs during an inspiratory 

 movement, then all those muscles may be regarded as elevators of the 

 ribs whose origin and insertion approach each other. Hence, only 

 these muscles can be designated as muscles of inspiration. From this 

 point of view the scalene muscles, the long and short elevators of the 

 ribs, and the posterior superior serratus are to be recognized as un- 

 doubted inspiratory muscles. They are also to be considered as the 

 muscles having the greatest influence on the ribs during inspiration. 



Of the intercostal muscles, according to this experiment, only the 

 external and the intercartilaginous portions of the internal can be desig- 

 nated as inspiratory muscles. The remainder of the internal (the parts 

 covered by the external) are lengthened during elevation of the ribs, 

 and shortened when the ribs are lowered. As a muscle always exhibits 

 its activity by shortening, the internal intercostal muscles have been 

 regarded as depressors of the ribs (that is, as expiratory muscles). 



Fig. 8 1, I, shows that when the rods a and b, representing the depressed ribs, 

 are elevated, the interspace (intercostal space) must become wider: ef >cd. On 

 the left side of the figure it may be seen that when the rods are elevated, the line 

 g h, representing the external intercostal muscles, is shortened (i k < gh) , while 1 m, 

 representing the internal intercostals, is lengthened (1 m < o n). Fig. 81, II, 

 shows that the intercartilaginous muscles, designated by g h, and the external 

 intercostal muscles, designated by 1 k, are shortened by elevation of the ribs. 

 The latter position of these muscular fibers may be represented by the shortened 

 diagonals of the dotted rhomboids. 



The controversy over the mechanism of the intercostal muscles dates back 

 to ancient times: Galen (131-203 A. D.) regarded the external intercostal muscles 

 as inspiratory and the internal as expiratory muscles. Hamburger (1727), fol- 

 lowing Willis' investigations, agreed with this view, and also recognized the inter- 

 cartilaginous muscles as inspiratory muscles. A. v. Haller, who was Hamburger's 

 direct opponent, considered both internal and external intercostals as muscles of 

 inspiration; while Vesalius (1540) regarded them both as expiratory muscles. 

 Masoin and R. du Bois-Reymond admitted the latter view, but only for forced 

 respiration. Finally, Landerer, who observed that the upper two or three inter- 

 costal spaces became narrower during inspiration, believed that both sets were 

 active during both inspiration and expiration. As they hold the ribs together, 

 they have the sole function of transmitting the traction imparted to them simply 

 through the chest-walls. They would, therefore, remain active even when the 

 distance between their points of insertion becomes greater. 



After mature consideration of all the conditions, Landois was unable to accept 

 any of these views unconditionally. It is obvious that the external intercostal 

 and intercartilaginous muscles can" act together only during inspiration, while the 

 internal can be active only during expiration (the latter statement having been 

 confirmed by Martin and Hartwell in dogs by means of vivisection) ; but elevation 

 and depression of the ribs are not the chief results attained by the action of these 

 muscles. It was rather Landois' opinion that the chief purpose of the external 

 and intercartilaginous muscles is to counteract the inspiratory widening of the 

 intercostal spaces and the synchronous increase in the elastic traction of the lungs. 

 The function of the internal intercostal muscles is to offer resistance to the ex- 

 piratory distention that occurs during, forced expiratory efforts, as in coughing. 

 Without muscular resistance the intercostal tissues would be so stretched through 

 the uninterrupted traction and pressure that regular respiratory movements would 

 become impossible. 



The lesser pectoral (and the greater anterior serratus ?) is capable of 

 assisting in the elevation of the ribs only when the shoulders are held 

 in a fixed position, partly through a firm propping up of the arms, and 

 partly by the rhomboid muscles, as is instinctively done by dyspneic 

 patients. 



