MUSCULAR CONTRACTION 



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thing takes place as when we raise our own forearm. This 

 action is performed by means of the biceps muscle which 

 arises from the scapula and is inserted into the fore-arm. 

 When the latter is raised we feel a lump rise on the front of 

 the upper arm due to the thickening of the biceps. 



Fig. 17. — Diagram of apparatus for demonstrating the contraction of the ga.stroc- 

 nemius muscle. 

 A, upright bearing two adjustable horizontal arms. To the upper of these (B) is fi.xed 

 by a clamp, the femur 0^). having the gastrocnemius i^sfr) in connection with 

 it. To the lower arm (C) is fixed alight lever (L) moveable in a vertical plane, 

 and ha\-ing the tendon of insertion of the muscle attached to it by a thread. 

 The dotted lines show the form of the gastrocnemius and the position of the le%er 

 during contraction of the muscle, sc. iiz'. the sciatic nerve. 



This shortening and thickening of the muscle is termed 

 a contraction. Do not fail to notice that this word is used 

 in a special sense. When we say that a red-hot bar of iron 

 contracts on cooling we mean that it becomes smaller in all 

 dimensions — undergoes an actual decrease in bulk. But in 

 muscular contraction there is no alteration in bulk : the 



