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A TEXTBOOK OF PHYSIOLOGY 



they come together. In people with ill-developed chests there is but 

 little movement here. The posterior part of the apex of the lung is 

 but little affected by the movement of the operculum, its expansion 

 being secured by diaphragmatic breathing. 



The Movement of the Upper Ribs. It is on these that most 

 of the observations upon rib movements and the action of the 

 intercostal muscles have been made. During inspiration, both sets of 

 intercostal muscles act together, and draw up the upper ribs towards the 

 operculum, which acts as a fulcrum. During expiration, the lower set 

 of ribs are fixed, and act as fulcrum, and the upper set are drawn down 

 toward them by the intercostal muscles. This view of the action of 

 the intercostals is not accepted by everyone. There is some experi- 

 mental evidence to show that the external intercostal muscles act 

 during inspiration. The fibres slant from above downwards and for- 



VII Cer* Vert- 

 Neck of I'tRib 

 Apex of Lung - 

 l*!Rib(inspir.)-- 



2 nd Rib 



Ma n ub. (inspirj 

 Manub.fexp.) 

 StMan.Jt. 



St.Man.Jt. 



Lungdnsp.)- 



FiG. 152. DIAGRAM TO SHOW RESPIRATORY MOVEMENTS OF THE FIRST PAIR OF RIBS 

 AND MANTBRIUM STERXI AND THE EFFECT OF THESE MOVEMENTS ON THE EXPAN- 

 SION OF THE APEX OF THE LUNG. (Keith.) 



wards, and. shortening, raise the ribs. The fibres of the internal 

 intercostals. on the other hand, slant from above downwards and 

 backwards, and. shortening, lower the ribs. The two, acting together, 

 make rigid the thoracic wall. The intercartilaginous fibres act with 

 the external intercostals. 



The Movement of the Lower Ribs. The purpose of the movement 

 of the lower ribs is to expand the lower lobe of the lung. The dia- 

 phragm i* the chief muscle concerned, aided by the ilio-costalis, and 

 the external intercostals, and the interchondral muscles. The an- 

 tagonistic muscles are the external oblique, the internal oblique, 

 and the trajisversalis. During inspiration, owing to the mode of 

 articulation of the ribs, the lateral and anterior part of each moves 

 outwards more than the one above. At the same time, the lower ribs 

 are raised, together with the sternum, so that the net result of the 

 lower rih movement is to increase the transverse and back-to-front 



