450 



applied to the bones. It is evident that if a similar process 

 were carried on with the cassava press, and the central 

 portion forcibly distended, the supports at either end would be 

 drawn powerfully towards each other. Substitute the muscle 

 for the press, and the bones for the poles, and this is muscular 

 action. 



Here we have a diagram which speaks for itself, as far as 

 muscular action is concerned, but there is another point to 

 which we shall presently pass. 



The muscle of the arm is seen running along the bone, 

 passing over the elbow, where it is held down by a tendinous 

 band, and, by its contraction, enabling the arm to be bent so as 

 to uphold a considerable weight. The mechanical analogy 



HUMAN ARM. STEELYAED. 



between this arrangement and the common Steelyard is too 

 evident to need any explanation except inspection of the 

 diagram. 



There is, however, another point which is worthy of con- 

 sideration. The muscle does not proceed at once from the 

 shoulder to the wrist, but passes under the tendinous band 

 above mentioned, and so produces a change of direction when 

 the arm is bent. 



There is a more complicated arrangement of a similar 

 character in the human hand, a diagram of which is given in 

 the left-hand figure of the accompanying illustration. 



The fingers are, of course, moved by a set of tendons, and 

 the muscles, from which these tendons spring, are attached to 

 the fore-arm (I purposely omit the scientific titles, though 

 they would be much easier to write). Any of my readers can 

 prove this for themselves. 



