116 MECHANISM OF THE MUSCLES. 



the muscle seems to act of its own accord ; this Is 

 about all the explanation our knowledge of the subject 

 at present enables us to give ; except that there are 

 little shining threads, called the nerves, and which 

 are fine branches of the spinal marrow or brain, that 

 enter into all the muscles, r and which, if divided or 

 injured, the muscle is deprived of all its power. 

 When the muscle shortens, it swells. If we bend the 

 arm, and grasp it at the same time, a little above the 

 elbow, we feel a swelling under the hand ; — the mus- 

 cle, which contracts, and produces the flexure, being 

 situated in that part of the arm. 



T. As you have a clear idea, I perceive, of 

 a muscle, we will look at some of the examples of 

 Creative skill and design in this part of our structure. 

 If an artist were to contrive a machine with wires 

 and strings to produce an imitation of our motions, 

 how would he apply his apparatus to effect opposite 

 movements with the same part ? — to make the arm, 

 for example, move backward and forward ? 



A. Wherever a string was employed to pull for- 

 ward any part, there would be a corresponding one 

 on the opposite side to draw it back ; and all the 

 strings would be divided into pairs for this purpose. 

 It is exactly the same in the living structure. The 

 muscles are in pairs. To move the arm forward 

 there is a muscle before ; to move it backward there 

 is a muscle behind. It were difficult to conceive 

 what could be more expressive of design. 



B. In the five hundred and twenty-seven muscles, 

 therefore, we have as many separate arguments of 

 design, as there are pairs, into which the muscles 



