104 THE MUSCLES. 



ton which is situated between the bone to be moved and the 

 centre of the body ; for example, the muscles which move the 

 head are situated on the neck ; those which move the arm are on 

 the shoulder; those which flex and extend the fore arm surround 

 the humerus, and those which flex and extend the fingers are 

 placed upon the fore-arm ; the same is true of the muscles of the 

 lower extremities. 



64. The muscles are divided into flexors, extensor^ rotators, 

 elevators, &c. according to the uses which they subserve. 



65. The contraction of the muscles is determined by the ac- 

 tion of the nervous system, and each muscle receives a nerve 

 which is ramified in its substance. 



66. This contraction is sometimes effected through the influ- 

 ence of the Will and sometimes independently of it. 



67. The muscles whose action is dependent upon the Will be- 

 long to the functions of relation, and those whose motions are 

 involuntary (the heart for example) belong to the functions of 

 vegetative life. 



68. The strength or power of a muscle depends partly upon its 

 volume, and partly on the manner of its attachment to the bone 

 which it moves. 



69. All things being in other respects equal, the strongest mus- 

 cles are the largest, and from exercise both their volume and 

 strength are at the same time increased. 



70 In the bodies of animals, the muscles and the bones are 

 generally placed unfavourably for the power of motion, but very 

 favourably for rapidity, as may be easily demonstrated by the 

 elementary principles of mechanism. 



71. The muscles not only serve to enable us to execute dif- 

 ferent motions, but they are also equally necessary to maintain 

 the moveable bortes in the positions proper to them, and their 

 action determines the attitudes. 



For example, the head by its own weight has a tendency to 

 fall forward, but the contraction of the muscles on the back of the 

 neck keep it erect 



64. How are the muscles divided? 



65. What determines the contraction of the muscles? 



. 06. Is muscular contraclion always the result of the influence of the will? 



67. To what principal functions do the muscles belong ? 



68. Upon what does the string 11 h or power of a muscle depend ? 

 6 f ). What is the effect of exercise upon the muscles ? 



70. Whether are the muscles and bones arranged more with a view to 

 power or rapidity ? 



71. Do the muscles serve any other purpose than to produce motion ? 



