THH EEASON WHY. 225 



1 Tliou hast clothed me with skin and flesh, and hast fenced me with bones and 

 sinews." JOB xi. 



tendons fastened at the ends of the fingers, contract, and by 

 becoming shorter, draw the fingers upward, and towards the 



944. Why can we throw lack the fingers after they have 

 teen raised? 



Because the muscles at the back of the arm, whose tendons are 

 attacked to the back of the fingers, contract and restore them 

 to their former positioa. 



945. What degree of strength do the muscles possess ? 



The degree of strength of a muscle depends upon the healthy 

 condition of the muscle, the amount of stimulus which it receives at 

 the time of exertion, and the manner in which its powers are 

 applied. 



The great muscle of the calf of the leg has been found, when 

 removed from a dead body, to be capable of sustaining a weight 

 equal to seven times the weight of the entire body 



But the contractile power of the living muscles is very great: 

 the thigh bone has frequently been broken by muscular contractions 

 in fits of epilepsy. And in cases where there has been a dislocation 

 of the thigh, the head ofthe thigh-bone being thrown out of its 

 socket, (Fig. 56) it has been found necessary to employ strong 

 ropes, attached to a wheel turned by several hands, in order to 

 overcome the contraction of the excited muscles, and to enable the 

 operator to restore the bane to its place. 



946. What is the stimulus which sets the muscles in 

 action ? 



The muscles are excited to action by the nerves, which they 

 receive from the spinal cord. 



047. Why does it require the influence of the ^oitt to set 

 the arms in motion ? 



Because the muscles which form their mechanism are voluntary 

 muscles that is, they are subject to the will of man, and j 



