OF MUSCULARITY AND ELASTICITY 



81 



FIG. 24. 



from the spring of the bow, the extremities of the 

 bow drawing obliquely on the string. 



To free breathing, it is necessary that the ribs 

 shall approach each other, and this is performed 

 by certain Intercostal muscles (or muscles play- 

 ing between the ribs), and now we can answer 

 the question, why are the fibres of these muscles 

 oblique ? 



Let us suppose this figure to represent two ribs 

 with thin inter- 

 vening muscles. 

 If the fibres of 

 the muscle were 

 in the direction 



A, across, and 



perpendicular to the ribs ; and if they were to 

 contract one third of their length, they would not 

 close the intervening space they would not ac- 

 complish the purpose. But being oblique, as at 



B, although they contract no more than one third 

 of their length, they will bring the ribs C, D 

 together. By this obliquity of the intercostal 

 muscles, they are enabled to expand the chest 

 in inspiration, in a manner which could not be 

 otherwise accomplished. 



In the greater number of muscles the same 

 principle directs the arrangement of the fibres; 

 they exchange power for velocity of movement, 

 by their obliquity. They do not go direct from 



