MOVEMENTS.] PHYSIOLOGY, 31 



something rise up. You feci the biceps getting 

 thicker as !^ is getting shorter in order to 

 bend the arm. 



The shortening does not last for ever. Sooner or 

 later the muscle lengthens again, getting thinner once 

 more, and so returns to its former state. The lengthened 

 condition of the muscle is the natural condition, the 

 condition of rest. The shortening or contraction 

 is aij effort which can only be continued for a certain 

 time. The contraction bends the arm, and as long 

 as the muscle remains shortened the arm keeps 

 bent ; but as the muscle lengthens, the weight of the 

 hand and fore-arm, if there is nothing to prevent, 

 straightens the arm out again. 



It is in the muscle alone, in the belly made 

 up of muscular fibres, that the shortening 

 takes place. The tendons do not shorten at all. 

 On the contrary, if anything they lengthen a little, 

 but only a very little, when the muscle pulls upon 

 them. Their purpose is to convey to the bone 

 the pull of the muscle. They are not necessary, 

 only convenient. It would be possible but awkward 

 to do without them. Suppose the fleshy fibres 

 of the biceps reached from the shoulder-blade to 

 the /ore-arm : you could bend your arm as before, 

 but it would be very tiresome to have the muscle 

 swelling up in the inside of the elbow, or on the top 

 of the shoulder : in either place it would be very much 

 in the way. By keeping the fleshy, the real contracting 

 muscle, in the arm, and carrying the thin tendons to 

 the arm and to the shoulder, you are enabled to do 

 the work much more easily and conveniently. 



Well, then, we have got thus far in understanding 



