78 



THE HUMAN MECHANISM 



branches extend as far anteriorly as the lower parts of the 

 brain. As shown in the figure, these branches give off at 

 right angles to themselves subbranches (the collaterals), each 

 of which enters the gray matter and ends there by breaking 

 up into a tuft of extremely fine fibrils, the synapse. The 

 synapse is in close proximity to, and possibly in a kind of 

 anatomical continuity with, the dendrites or the main body 



A B 



FJG. 44. Relation of afferent (of) to efferent (ef) neurones of the spinal cord 



In A the single afferent neurone branches into six collaterals, each of which ends 



in a synapse around an efferent cell. In B the connection is made through the 



agency of the cell a, as explained in section 13 



of a nerve cell of the gray matter. Each afferent neurone, 

 then, is a cell whose main body is in the ganglion of the 

 dorsal root and whose branches, or arms, reach out, one of 

 them to a peripheral sense organ and the other to the gray 

 matter of the spinal cord and brain, where they end in 

 synapses. By means of the synapses the afferent neurone 

 excites or stimulates other neurones. 



9. Anatomical relation of afferent to efferent neurones. We 

 may now put together what we have learned about the 

 neurones of the ventral and those of the dorsal root; we 



