238 THE ACTION OF THE INTERCOSTAL MUSCLES. 



raised, the intercostal spaces are widened. (6.) When the upper ribs 

 are raised, all the lower ribs and the sternum must be elevated at the 

 same time, because all the ribs are connected with each other by means 

 of the soft parts of the intercostal spaces, (c.) During inspiration, 

 there is an elevation of the ribs and a dilatation of the intercostal 

 spaces. (The lowest rib is an exception; during forced respiration, at 

 least, it is drawn downwards), (d.) If, on a preparation of the 

 chest, the ribs be raised as in inspiration, we may regard all those 

 muscles as elevators of the ribs, whose origin and insertion become 

 approximated. Everyone is agreed that the scaleni and levatores 

 costarum longi et breves, the serratus posticus superior, are inspiratory 

 muscles. These are the most important inspiratory muscles which 

 act upon the ribs. 



Intercostal Muscles. With regard to the action of the intercostal 

 muscles, there is a great difference of opinion. According to the 

 above experiment, the external intercostals and the intercartilaginous 

 parts of the internal intercostals act as inspiratory muscles, whilst the 

 remaining portions of the internal intercostals (as far as they are 

 covered by the external) are elongated when the ribs are raised, while 

 they shorten when the chest-wall descends. A muscle shortens only 

 during its activity. The internal intercostals were regarded by Ham- 

 berger (1727) as depressors of the ribs or expiratory muscles. 



In Fig. 106, I, when the rods, a and b (which represent the ribs) are raised, the 

 intercostal space must be widened (e/> c d). On the opposite side of the figure, 

 it is evident that when the rods are raised, the line, g h, is shortened (ik<:gh, 

 direction of the external intercostals) I m is lengthened (I m < o n, direction of 

 internal intercostals). Fig. 106, II, shows, that when the ribs are raised, the inter- 

 cartilaginei, indicated by g h, and the external intercostals, indicated by I k, are 

 shortened. When the ribs are raised, the position of the muscular fibres is 

 indicated by the diagonal of the rhomb becoming shorter. 



The mode of action of the intercostal muscles is an old story. Galen (131-203 

 A.D.) regarded the externals as inspiratory, the internals as expiratory. Hamberger 

 (1727) accepted this proposition and considered the intercartilaginei also as inspira- 

 tory. Haller took both the external and internal intercostals as inspiratory, while 

 Vesalius (1540) regarded both as expiratory. Landerer observing that the upper 

 two or three intercostal spaces became narrower during inspiration, regarded both 

 as active during inspiration and expiration. They keep one rib attached to the 

 other, so that their action is to transmit any strain put upon them to the wall of 

 the chest. On this view they will be in action, even when the distance between 

 their points of attachment becomes greater. Landois regards the external inter- 

 costals and intercartilaginei as active only during inspiration, the internal 

 intercostals only during expiration. [Martin and Hartwell exposed the internal 

 intercostals and observed whether they contracted along with the diaphragm, or 

 whether the contractions of these two muscles alternate. As the result of their 

 experiments, they conclude that "the internal intercostal muscles are expiratory 

 throughout their whole extent, at least in the dog and cat; and that in the former 

 animal they are almost ' ordinary ' muscles of respiration, while in the latter they 

 are 'extraordinary' respiratory muscles."] Landois is of opinion that the chief 



