A PAIR OF LIVING BELLOWS 127 



which we have already looked at. In the forearm the 

 hinge or fulcrum is at the elbow-joint ; the weight is 

 placed in the hand ; the engines which work the lever are 

 the two brachial muscles — one placed in front of the arm, 

 the other behind it (fig. 7, p. 42). The 7th rib also has 

 its fulcrum, its engines and load. The backbone serves 

 as its fulcrum, but the attachment is of a peculiar kind — 

 one which has not been rightly explained before. The 

 whole of that part of a rib-lever which is situated in the 

 back of the body forms a fulcrum or axis round which 

 the front end of a rib is raised or lowered. The hinder 

 end of the 7th rib is held in position, firstly, by liga- 

 ments which tie it to the backbone ; secondly, by the 

 muscles which keep the spine erect ; they are attached to 

 the hinder segment of the 7th rib — as to all ribs — in such 

 a way that they fix it and maintain it in position when 

 the front part of a rib is ascending or descending. Thus 

 muscular engines are actually employed in holding or 

 balancing the axis on which a rib turns. 



Having seen how the 7th costal lever is joined to the 

 backbone, we turn to examine the engines which make 

 it move so that it expands and compresses the respiratory 

 bellows. In fig. 31 part of a sheet of muscle is repre- 

 sented as rising from the backbone and passing forwards 

 and downwards to catch hold of the 7th rib. This is 

 part of the muscular engine which raises the rib ; the 

 backbone is the fixed base from which it pulls. But 

 it will be noticed that certain lines cross the sheet of 

 muscle thus depicted (fig. 31) ; these are to indicate that 

 in reality the muscular sheet that lifts the 7th rib is 

 interrupted — is broken into short intercostal segments — 

 by the ribs immediately above the 7th. These ribs have 

 been plucked out from the sheet as it were. In reality 

 the muscular sheet which lifts the 7th rib is not a single 

 big engine but a string of engines, but as far as the pull 

 on the 7th rib is concerned the result is the same whether 

 there is one long or many short engines. Then in fig. 3 1 

 part of another muscular sheet is seen ascending to the 

 7th rib ; the fixed basis from which it acts is the pelvis ; 



