ACTIOX OF INSPIRATORY MUSCLES. 313 



motion in the middle of tlieir arch ; and in the living subject, the ribs, in their 

 elevation, both rotate upon then- axis and bend u^jon themselves, instead of 

 describing a simple upward and downward movement like the bars, so that 

 it is impossible to di-aw any certain conclusion from such imperfect imitations 

 of the mechanism. On the whole, the deficiency of the external intercostal 

 muscles in front and of the internal behuid, in which situations they would have 

 acted as depressors, seems to point to a combined action of the muscles as eleva- 

 tors of the ribs in the manner maintained by Haller. This view is farther 

 supported by the result of experiments on the galvanic stimulation of the 

 intercostal muscles. Thus Duchenne found (Physiol, des Mouvements, &c., p. 

 647) that the direct galvanic stimulation of the external intercostal muscles 

 throughout the iifth space caused the lower ribs to rise ; towards the upper, and 

 likewise that the stimulation of the internal intercostal muscles in the inter- 

 cartHaginous part of the space also caused the lower rib to rise, and he fai-ther 

 found that when the galvanic stimtdus was so strong as to reach the mtercostal 

 nerve, and throw the whole of the internal as well as the external mtercostal 

 muscles into action, the lower ribs were still elevated. These results received 

 additional conhrmation from the pathological observation that in cases of 

 paralysis of the diaphragm and the auxiliary muscles of insphation the ribs were 

 raised by the sole action of the intercostal muscles, and that in other cases in 

 which the intercostal muscles were paralysed, while the diaphragm retained its 

 power, the expansion of the upper ribs was enthely abolished. 



Among the more recent anatomical wiiters, Henle inclines to Haller's view ; 

 Luschka refers to Budge's experiments on the muscles of Living animals, as 

 proving that the internal intercostal muscles elevate the ribs (Budge, '• Lehi-buch 

 der Physiologic des Menschen," Weimar, 1800, p. 70^. 



The levatores costarum have a similar action with the posterior fibres of the 

 external intercostal muscles, and ought therefore to be ranked among the agents 

 of inspiration. The scalene muscles also are usually believed to contril^ute, even 

 in normal and quiet inspiration, to the support and elevation of the first and 

 second ribs and it is obvious that the serratus posticus superior must have a 

 similar effect on those upper ribs to which it is attached. 



The action of the duipJn'agm is more easily understood than that of the inter- 

 costal muscles. By its contraction and descent its convexity is diminished, the 

 abdominal viscera are pressed do'miwards, and the thorax expanded vertically. 

 The fibres arising from the lowest ribs, beiug directed nearly vertically upwards 

 from their costal attachments^ must tend to pull those ribs upwards. Duchenne 

 has showTi that the contraction of the diaphragm by itself elevates and expands 

 the lower ribs, but only so long as the vault of the muscle is supported by the 

 abdominal viscera, for when they are removed it no longer has that action (op. 

 cit. p. G20). The serratus posticus inferior and quadratus lumborum muscles, by 

 opposing the diaphragm, and thus giving it a fixed point on which to descend, 

 become assistant muscles of inspiration. The anterior fibres of the diaphragm 

 being directed more horizontally towards the central tendon, oppose the forward 

 motion of the sternum ; hence the sternum becomes arched in patients long 

 subject to asthma. (Hutchinson, Article " Thorax,'' in Tocld s '' Cyclopasdia of 

 Anatomy and Physiology ; " Meyer, " Physiologische Anatomic.") 



In more forcible inspiration, and more especially in severe attacks of dyspnoea, 

 there are called into play other powerful muscles, to secure the rnsj)iratory action 

 of which a fixed attachment mr.st be provided by the supporo and elevation of 

 the shoulder and arm ; among these may be enmne'ated the serratus magnus and 

 pectoralis minor, acting from the shoulder, and the pectoralls major and latissimus 

 dorsi, acting from the raised aim, which together produce expansion and eleva- 

 tion of the ribs. 



Uxpirafion. — In normal and quiet expiration the diminution of the capacity 

 of the chest is mainly, if not wholly due to the return of the walls of the 

 chest to the condition of rest, in consequence of their own elastic re-action, and 

 of the elasticity and weight of the viscera and other parts displaced by inspira- 

 tion ; the lungs themselves, after distension by an-, exert considerable elastic 

 force, and no doubt the ribs and their cartilages react strongly by their elastic 



