THE STORY OF THE BRAIN AND NERVE 113 



given off by a double root from the spinal cord 

 was made plain. One root is named the anterior 

 root, because it is given off from the front of the 

 spinal cord, the other, the posterior, proceeding 

 from the hinder portion. Shortly after leaving the 

 cord, the two roots unite to form a single spinal 

 nerve. The hinder root of each spinal nerve may 

 be distinguished by the fact that it possesses a 

 ganglion or small collection of nerve cells. The 

 proper understanding of the manner in which the 

 nervous system operates, and especially how reflex 

 action is carried out, was made clear by researches 

 showing the functions of these two roots. If the 

 front root be cut in an animal, whilst the hinder is 

 left intact, the animal loses the power of movement 

 in the parts to which the nerve is distributed, but 

 retains the power of sensation or feeling. If the 

 posterior or hinder root be cut, on the other hand, 

 and the front root left untouched, the opposite 

 result is seen, the animal retaining the power of 

 movement in the parts, but losing the power of 

 feeling. From these facts it is clear that each 

 ordinary nerve in the body comprises two sets of 

 fibres, those derived from the front and hinder roots 

 respectively- The experiment described shows that 

 messages passing from the brain and spinal cord to 

 the body pass out by the front roots of the spinal 

 nerves, and are conveyed to the body by the fibres 

 which represent the continuation of these roots. 

 On the other hand, messages coming from the body 

 to the brain and spinal cord pass along the fibres 

 of nerves belonging to the posterior or hinder root, 

 and then entering the cord, are subsequently dealt 

 with either by the cord or by the brain, to which 

 the messages, if need be, can be conveyed. The 



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