THE HUMAN HAND ; A SCHOOL LESSON 35 



free to move yields to the pull and changes its position. 

 When you bend your finger or your arm, you do so by 

 the help of masses of fleshy fibres, which contract in con- 

 sequence of an impression received through a nerve, and 

 probably starting from the brain. Nerves of sensation 

 and nerves of motion are often both concerned in the 

 movements of a limb. If, for instance, I happen to put 

 my finger on a cinder which is so hot as to burn, I lift 

 the finger as quickly as possible. What happens is this. 

 A nerve of sensation conveys to the nerve-centres an 

 impression of pain ; the nerve-centres send an urgent 

 message along another nerve (a nerve of motion) to a 

 particular muscle, commanding it to contract. The 

 muscle contracts and the finger is raised. 



The fingers are capable of a number of distinct move- 

 ments. They can be bent (flexed), stretched (extended), 

 moved towards the middle line (adducted), or moved away 

 from it (abducted). The thumb and in a less degree the 

 fore finger can be moved in any of these ways independently, 

 but the remaining fingers are inclined to move together, 

 and do not easily move to any considerable extent one 

 by one. The playing of musical instruments, especially 

 the piano and violin, trains them to independent move- 

 ment. You will remark that you can flex the fingers 

 more powerfully than you can extend them, and the 

 same is true of other parts of the body also. When we 

 lie quite at our ease, as in bed, the limbs are a. little bent, 

 because the flexors are more powerful than the extensors. 

 In many animals the inequality is much more marked 

 than in man. 



Look at the front or palm side of your wrist, and you 

 will see two cords beneath the skin, which are evidently 

 concerned in flexion, for they stand out more plainly when 

 the hand is strongly bent. In a thin arm other cords can 

 be made out besides the two just mentioned. All these 

 are flexors of the wrist and hand. Deeper in the wrist 

 and palm, so that they can only be seen by dissection, are 



