CHAPTER IV 



ARE OUR MUSCLES REALLY INTERNAL-COMBUSTION 

 ENGINES ? 



We must now look more closely into the machinery of 

 a muscular engine. In the last two chapters we have been 

 merely counting over the number of these engines in the 

 human body, and noting how they set the bones in motion 

 when we walk. The engines set the limbs moving, just 

 in the same way as the internal-combustion engine of a 

 motor cycle makes the hind wheel go spinning round. 

 The muscular engine we are to choose for our present 

 purpose is one which everybody can study, namely, the 

 biceps muscle, placed in front of the right arm. It is not 

 difficult to feel it in action ; you have only to clasp the 

 part of the arm in which it lies with the left hand, and 

 then, as the elbow is bent and the right hand rises towards 

 the face, it is felt to become thicker, harder, and shorter. 

 That is what happens to every muscular engine when it 

 is set in motion. In the drawing shown in Plate II. the 

 biceps is seen stretched out and lying side by side with 

 other muscular engines, but in fig. 4 all of these have 

 been taken away, so that we may devote our attention to 

 the biceps alone. We must first look at the manner in 

 which it is fixed to the base or fulcrum from which it 

 exerts its power. We see that it is fixed by two heads — 

 hence its name. Both of these are attached to the shoulder- 

 blade or scapula, one just above the shoulder-joint, the 

 other to a finger-like process of bone called the coracoid. 

 Its tendon or piston cord ends in the forearm, being fixed 

 mainly to the radius, one of the two bones in the fore- 



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