LECTURE IX. 



THE ROOTS OF THE PERIPHERAL NERVES, THE SPINAL GANGLIA, 



AND THE SPINAL CORD 



GENTLEMEN: The peripheral nerves are made up, as you 

 know, of both motor and sensory fibres. In the vicinity of the 

 spinal cord these fibres are separated. The branch containing 

 the motor fibres passes directly into the spinal cord as an 

 anterior root. The sensory fibres pass into the spinal ganglion. 



Situated in the spinal ganglia are a number of large mono- 

 polar cells (occasionally bipolar). In the case of a monopolar 

 cell the process generally divides shortly after leaving it, so that 

 here also we have two processes. 



Your attention was called to these two processes of the 

 cells of the spinal ganglia in the second lecture. You will 

 recollect that, according to the observations of His, the sensory 

 nerves are evolved from cells in the form of a process extending 

 toward the periphery, and that these cells also send out another 

 fibre toward the spinal cord which forms the posterior root. 



Since the careful examination made on adults shows that 

 about as many fibres pass through the posterior root to the 

 spinal cord as have entered the ganglion from the nerves, it 

 would seem as though a single cell were intercalated in the 

 course of each fibre. 



It is, however, a matter of great importance to determine 

 whether all sensory nerves originate in the cells of the spinal 

 ganglia. This question has been fully settled by the experi- 

 ments of Waller and others, and by the most recent experiments 

 of Joseph. 



Every nerve-fibre which is divided from its mother-cell de- 

 generates. If a sensory nerve is divided just in front of the 



(147) 



