POSTURAL COORDINATION 923 



up by tapping the tendons from controlling the activity of the motor 

 part of the reflex arc (see the Final Common Path, page 945). If the 

 leg of an animal be thrown into flexion, the extensor muscles are in- 

 hibited from contraction and the knee jerk can no longer be elicited, 

 even though the extensor muscles are separated from their insertion 

 and consequently do not have to pull against the contraction. In a 

 similar way the knee jerk may be inhibited by influences arising in 

 the cerebrum, and consequently it is frequently necessary to distract 

 the subject's attention before the response can be brought out. 



