MUSCLES 37$ 



greater than the weight which they move. But the outef 

 end of a lever moves over a greater distance in a given 

 time than the part near the fulcrum. So if a muscle 

 loses power by its attachment to a bone, it gains in rapidity 

 of motion. The muscles of the body are strong enough to 

 combine strength with quickness of motion. 



The joints of the arms and legs are mostly so arranged that the limb 

 can form a straight line, but can be bent in only one direction. The 

 muscles which bend a limb are called the flexors, while those which 

 straighten it are called extensors. Flexor and extensor muscles are" 

 usually arranged in opposing pairs, with the flexors upon the front and 

 the extensors upon the back side of the limb. The flexor of the elbow 

 reaches from the elbow to the shoulder upon the front of the arm and 

 is called the biceps. The extensor of the elbow extends in the same 

 way upon the back of the arm and is called the triceps. Both the flexors 

 and extensors of the wrist and fingers are situated between the elbow 

 and the wrist. Only a few small ones are in the hand. 



The muscles which flex the knee end in strong tendons which can 

 be felt as the hamstrings upon the back of the joint. The muscles 

 which extend the knee end in a single large tendon inside of which is 

 the patella. The patella acts as a pulley to protect the joint from the 

 action of the tendon. 



The muscles of the ankles and toes are arranged much like those of 

 the wrist and fingers. By practice while young, it is possible to learn 

 to use the toes in the same way as the fingers. 



671. Back muscles. The backbone is held upright and 

 bent backward by large mustles which form ridges upon 

 each side of the spine. They stretch the whole length of 

 the spine so that the weight and power are at the same 

 place while the fulcrum is the point of bending. Thus the 

 spine is equivalent to a lever of the second or third class 

 which uses most of the power of the muscle. So the back 

 possesses great power with slow motion. 



672. Standing is done by the contraction of the opposing flexof 

 and extensor muscles of the lower part of the body, so that the 



