346 APPENDIX. 



In whatever direction the limb is to be moved, the 

 movable point must necessarily be in the opposite direc- 

 tion ; the act of flexion requiring that it should be first 

 extended, and so the contrary. But when the flexors 

 and extensors are both in a state of tension, they mu- 

 tually counteract each other, and the limb is fixed. 



Every muscle, when it contracts, not only acts upon 

 the bone to which it is attached, but also on the antago- 

 nist, or opposite muscle, so that no one can act inde- 

 pendently of the other. 



Dr. Paley, in his Natural Theology, gives the follow- 

 ing familiar illustration of the action of the muscles : 

 " Every muscle is provided with an adversary. They 

 act like two sawyers in a pit, by an opposite pull ; the 

 nature of the muscular fibre being what it is, the pur- 

 poses of the animal could be answered by no other. 

 And not only the capacity for motion, but the aspect, 

 and symmetry of the body, is preserved by the muscles 

 being thus marshaled according to this order : for exam- 

 ple, the mouth is holden in the middle of the face, and 

 its angles kept in a state of exact correspondency, by 

 several muscles drawn against, and balancing each other. 

 In hemiplegia [paralysis of one side], when the mus- 

 cles of one side of the face are weakened, the muscles 

 on the other side draw the mouth awry." 



Contraction increases the Hardness of the Muscle. In 

 lifting a weight with the hand, the arm being extended, 

 the brachial muscle, situated between the elbow and 

 shoulder, acts with much force, and may be felt to in- 

 crease in size and hardness. This is the case with all 

 the muscles, when in a state of action, and those which 

 are most constantly employed, are increased in size and 

 firmness in consequence of such continued action. 

 Thus, the muscles of the right arms of blacksmiths are 

 always larger, and possess greater strength and density 

 than those of other men, in consequence of the continual 

 employment of this limb in their business. 



How is muscular contractihility shown by amputation ? What is said of 

 antagonist muscles ? What is the effect when antagonist muscles contract 

 at the same time? What is Dr. Paley's illustration of the action of the 

 muscles ? 



