412 



PHYSIOLOGY 



CHAP. 



(c) The external intercostals are inapiratory, the internal are 

 expiratory, with the exception of the intercartilaginous portions 

 (Spigel, Vesling, Bayle, and Hamberger, Hutchinson, A. Fick, 

 Martin, and Hartwell). 



(d) The intercostals are of no great importance in regard to 

 the movements of the ribs ; they serve rather to regulate tension 



PIG. 178. Deep muscles of anterior wall of thorax, seen from behind. (Allen Thomson.) , 

 Posterior part of rnanubrium sterni ; b, b, clavicle ; i-ix, anterior part of ribs and carti- 

 lages ; 1, 1', M. sterno-thyroidei ; 2, 2', M. sterno-hyoidei ; 3, 3', M. triangulares sterni ; 4, 4, 

 upper part of transverse muscles of abdomen which meet at 4' 4' of linea alba posterior ; 5, 

 insertions of diaphragm on lower ribs, crossing fascia of transverse muscles ; 5' bundles of 

 diaphragm inserted into ensiform process 1 ; 6, 6', intercostales interni ; 7, 7, 7, intercostales 

 externi, exposed by removal of interni. 



in the intercostal spaces, and to reinforce them during inspiration, 

 impeding their retraction by the increased negative intrathoracic 

 pressure (Henle, Meissner, Briicke, von Ebner, Landois). 



Criticism of these several theories would necessitate a prolonged 

 dissertation, disproportionate to the true importance of the 

 arguments and the scope of this text-book. Here we can only 

 summarise the facts that appear of most importance, and may 

 determine our choice among so many opinions. 



