ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 453 



With the motor impulses the case is different. When 

 the motor fibers of one side are cut that side is completely 

 paralyzed, even when the other side is left intact, showing 

 that the motor paths are direct. 



3. Summary of Nerve Paths. To summarize, then, 

 there are the following sensory paths : 



First. The neuron extending from the finger to the 

 spinal root ganglion and from there in turn to the posterior 

 horn of the spinal cord, may run directly to the anterior 

 horn and invest with its dendrons a motor cell there, and 

 so produce the path for the simple spinal cord reflexes. 



Second. The first sensory neuron may run not to the 

 motor cells, but to the cells forming Clark's column and in- 

 vest one of these with its dendron, which cell in turn as a 

 new neuron extends to the cerebellum and makes possible 

 the cerebellar reflexes. 



Third. The first neuron or branches of it may connect 

 with a neuron of the spinal cord which runs to the opposite 

 side of the spinal cord and there connects with other 

 neurons. This path makes possible the radiation of sensa- 

 tions to both sides of the spinal cord. 



Foitrth. The first neuron may connect with neurons 

 running to the cerebrum (a) by running up through the 

 posterior columns and connecting with the second neuron 

 in the medulla, which neuron there crosses and goes to the 

 opposite cerebral hemisphere; or (b) the first neuron after 

 ascending a short distance through the posterior column 

 enters the gray matter of the cord and there connects with a 

 neuron which crosses to the opposite side of the cord, and 

 in the antero-lateral tract reaches the cerebral hemispheres 

 the same as the neurons which cross in the medulla. 



4. Where Do the Sensory Neurons End in the Brain? 

 A very interesting question now arises, with what do these 

 sensory neurons connect in the cortex of the brain? While 

 this is possibly still debatable ground, it seems very proba- 



