MECHANICAL PHENOMENA OF RESPIRATION. 291 



form neither of these two functions: their principal office 

 being to complete the wall of the thorax by filling up the 

 intercostal spaces. It may be asked, however, if this could 



cases of progressive atrophy reported by Duchenne, that no men- 

 tion is made of the levatores costarum (surcostaux) , a subject on 

 which physiologists disagree as much as on that of the intercostals. 

 Duchenne gives no opinion either way, and it appears probable 

 that we shall be right in supposing the continuance of respiration 

 to be due to the persistence of these muscles. 2. They are both 

 expiratory: Vesalius, Diemerbrock, Sabatier. This is the opinion 

 held by Beau and Maissiat : according to them the intercostal 

 muscles come in play, especially when complex expiration takes 

 place (as in screaming or coughing) ; at such times, in vivisection, 

 the fibres of these muscles straighten and become tense, while in inspi- 

 ration they are depressed and look inwards towards the lung. These 

 physiologists adduce, in favor of their theory, an argument drawn 

 from comparative physiology: " The respiration of birds is known 

 to differ from that of the mammalia; expiration in birds is the 

 active, and inspiration only the passive, result of the elasticity of 

 the ribs, which spread apart, after having been pressed together by 

 the action of the expiratory muscles. Consequently, the intercos- 

 tal muscles, which exist in birds as well as in the mammifera, are 

 affected only in expiration. We cannot believe that those muscles 

 which are expiratory in birds are inspiratory in the mammifera." 

 3. The external intercostal muscles are expiratory, and the internal 

 inspiratory : Galien, Bartholin. 4. The external intercostal muscles 

 are inspiratory, and the internal expiratory : Spigel, Vesling, 

 Hamberger. This opinion is principally founded on study of 

 Hamberger's diagram (see Fig. 78, and his explanation, given 

 in the text). It has been somewhat modified by Sibson: " The 

 external intercostal between the thoracic set of ribs are through- 

 out inspiratory ; those portions between their cartilages are 

 expiratory, between the diaphragmatic set of ribs they are 

 inspiratory behind, expiratory at the side and in front, and be- 

 tween their cartilages they are inspiratory ; between the inter- 

 mediate set of ribs they are for the most part slightly inspiratory 

 between the ribs, and expiratory in front between the cartilages." 

 (" Mechanism of Respiration: Philosophical Transactions," 1847). 

 Though this theory seems to involve us in confusion and trifling 

 distinctions, if considered in a general point of view, we shall find, 

 with Hermann, that it leads to a simpler conception than at first 

 appears: " The external muscles are inspiratory in the bony parts 

 of the ribs, and the internal in the cartilaginous. As, however, 

 this is almost the chief action of the two directions of the fibres, the 

 intercostal may, in general, be classed among the inspiratory muscles " 

 (Hermann). 5. The external and internal intercostal are at once 

 inspiratory and expiratory : Mayow, Magendie. 6. The two inter- 

 costal muscles are passive in the movements of inspiration and expira- 



