202 THE MECHANISM OF 



tion, and action from the first to the twelfth ; to describe the 

 action and movement of each would cause the student to be lost 

 in detail. It is enough, in the writer's opinion, to -recognise that 

 in the thorax there are two parts which are functionally inde- 

 pendent ; these are (1) the upper mechanism connected with the 

 expansion of the upper lobe of the lung (the part above the great 

 fissure), consisting of the second, third, fourth, and fifth ribs, and 

 their attached muscles ; and (2) the lower mechanism, consisting 

 of the sixth, seventh, eighth, ninth, and tenth ribs, and their 

 attached muscles, designed for the expansion of the lower lobe. 

 In this lower mechanism the diaphragm is the dominating part. 

 The lower set of ribs is specially adapted to act with the diaphragm ; 

 they are an intrinsic part of the diaphragmatic mechanism. The 

 floating ribs, the eleventh and twelfth, and in 40 per cent, of bodies 

 the tenth also belongs to this group, are, from a functional point 

 of view, essentially a part of the abdominal wall ; their articula- 

 tions and movements are peculiar. The peculiar shape and action 

 of the first rib has already been described. In the writer's opinion 

 it is necessary, for a full analysis of the respiratory movements 

 in health and in disease, to distinguish four parts in the costal 

 series (1) The first rib, part of the thoracic operculum ; (2) the 

 upper costal series (second to fifth) ; (3) the lower costal 

 series (sixth to tenth), an intrinsic part of the diaphragmatic 

 mechanism ; (4) the floating series, functionally a part of the 

 abdominal wall. 



THE RESPIRATORY MOVEMENTS OF THE LOWER COSTAL SERIES 



The muscles and movements of the lower series are totally 

 different from those of the upper. The dominating muscle is the 

 diaphragm ; the other muscles are so arranged in their attach- 

 ments as to act either as synergic muscles (the ilio-costalis, the 

 external intercostals, the interchondrals) or as antagonists (the 

 external oblique, the internal oblique, the internal intercostals, 

 and the transversalis). The ribs of the lower series are articulated 

 to the spinal column in such a manner that the lateral and anterior 

 part of each moves outwards more than the one above it during 

 inspiration. The spinal part of each (50 to 70 mm. in length) 

 the part to which the erector spinse is attached rotates and 

 actually moves forwards (sternal-wards) during inspiration. The 



