136 THE HUMAN BODY. 



fibres present in a section made across the long axes of the 

 fasciculi, the greater the load that can be lifted or the other 

 resistance that can be overcome. On the other hand, the 

 extent through which a muscle can move a weight in- 

 creases with the length of its fasciculi. A muscle a foot in 

 length can contract more than a muscle six inches long, and 

 so would move a bone through a greater distance, provided 

 the resistance were not too great for its strength. But if 

 the shorter muscle had double the thickness, then it could 

 lift twice the weight that the longer muscle could. We 

 find in the Body muscles constructed on both plans; some to 

 have a great range of movement, others to overcome great 

 resistance, besides numerous intermediate forms which 

 cannot be called either long and slender or short and thick;, 

 many short muscles for example are not specially thick, 

 but are short merely because the parts on which they 

 act lie near together. It must be borne in mind, too, that 

 many apparently long muscles are really short stout ones 

 those namely in which a tendon runs down the side or 

 middle of the muscle, and has the fibres inserted obliquely 

 into it. The muscle (gastrocnemius) in the calf of the leg 

 for instance (Fig. 50, b) is really a short stout muscle, for 

 its working length depends on the length of its fasciculi 

 and these are short and oblique, while its true cross-section 

 is that at right angles to the fasciculi and is very large. The 

 force with which a muscle can shorten is very great. A 

 frog's muscle of 1 square centimeter (0.39 inch) in section 

 can just lift 2800 grams (98.5 ounces), and a human muscle 

 of the same area more than twice as much. 



Muscular Elasticity. A clear distinction must be made 

 between elasticity and contractility. Elasticity is a physi- 

 cal property of matter in virtue of which various bodies 

 tend to assume or retain a certain shape, and when re- 

 moved from it forcibly, to return to it. When a spiral 

 steel spring is stretched it will, if let go, "contract" in a 

 certain sense in virtue of its elasticity, but such a contrac- 

 tion is clearly quite different from a muscular contraction. 

 The spring will only contract as a result of previous distor- 

 tion; it cannot originate a change of form, while the tnus- 



