452 STUDIES IN ADVANCED PHYSIOLOGY. 



found here. It is this arrangement af the neurons of sensa- 

 tion and motion which makes the simple reflex actions of 

 the cord possible. 



Other branches or collaterals with their dendrons invest 

 cells found in Clark's column. These cells in Clark's 

 column are the beginnings of new neurons which reach 

 from Clark's column in the spinal cord to the cerebellum, 

 the fibers ascending in the direct cerebellar tract. In this 

 way sensations are carried to the motor cells of the cerebel- 

 lum and make the reflex actions of the cerebellum possible. 



None of the two paths just mentioned, however, result 

 in conscious sensation. There is a third path which leads 

 to the cerebrum itself. This path is about as follows: The 

 sensory nerves or branches from them, leave the posterior 

 horn of the spinal cord and ascend towards the brain through 

 the posterior columns. Many of these fibers run as far as 

 the medulla. In the gray matter of the medulla, however, 

 their dendrons invest new cells, nerves from which, after 

 crossing in the medulla, extend to the cortex of the brain. 



While most of the sensory fibers running up the pos- 

 terior column connect with their second neuron in the me- 

 dulla, many of them run into the gray matter of the spinal 

 cord before reaching the medulla, and there invest cells the 

 nerves from which then cross to the opposite side of the 

 spinal cord and reach the cortex of the brain. The path for 

 these crossed sensory fibers of the cord is the antero-lateral- 

 ascending tract. 



An additional sensory path needs mentioning. Some of 

 the branches or collaterals of the sensory fibers may con- 

 nect with neurons in the gray matter of the cord, which run 

 to the opposite side of the cord and connect with other 

 neurons there. That such paths exist is proved by the fact 

 that when the sensory fibers of one side of the spinal cord 

 are cut sensation is not lost, but seems actually for a little 

 while to be increased. This can, of course, only be ex- 

 plained by assuming that fibers must connect with the oppo- 

 site or uninjured side of the cord. 



