THE KEFLEX AKC 



413 



ness may accompany the action, it does not determine the 

 action. Many actions which are at first voluntary may 

 become reflex by repetition; and, in fact, one of the funda- 

 mental features of education is concerned in making reflex 

 or habitual, actions which in the child are voluntary and 

 require effort of will on his part. 



The reflex arc. — The spinal cord is the seat of most of 

 the reflex actions of the organs of the trunk and limbs. 



Fig. 191. — A spinal reflex. 



The relation of the nerve elements in simple reflexes which 

 have their origin in the cord, is shown in Figure 194, and 

 the relation there shown is typical of all reflex actions. In 

 this figure it will be seen that the posterior root of the spinal 

 nerve has on its surface a swelling which was called the 

 spinal ganglion. This ganglion contains many bipolar 

 nerve cells whose axones extend in different directions. 

 One axon passes out and forms one of the sensory fibers of 

 the spinal nerve. It terminates in some form of an end 

 organ. The other terminates in a brush in the gray 

 matter of the cord. Likewise, in the anterior cornua of the 

 cord is found a unipolar nerve cell whose dendrites are in 



