HuBER, Sympathetic Nervous System. 79 



axis of this second neuron ( the motor anterior horn cells ) 

 leaves the cord through the anterior root, enters a nerve trunk 

 and ends in an end-brush in a voluntary rnuscle fiber. 



In the other example chosen, the path involved in a sim- 

 ple reflex, the chain is also made up of two neurons. In this 

 instance the impulse originates in the end-brush of the dendrite 

 of a spinal ganglion neuron, is conveyed along the dendrite 

 to the cell body of the neuron in question, thence along 

 its neuraxis, which on entering the dorsal portion of the spinal 

 cord divides into an ascending and descending branch, from 

 which a number of secondary branches are given off (collateral 

 branches); some of these secondary branches terminate in an 

 end-brush in the anterior horn of the grey matter in adjunction 

 with the cell body or dendrite of a motor neuron, which forms 

 the second link in the chain. The impulses pass out along the 

 neuraxis of this cell to a voluntary muscle fiber. The two ex- 

 amples chosen may serve to illustrate the more modern con- 

 ception of the structure of the nervous system. 



If then the entire nervous system may be looked upon as 

 a complex of neurons, and if these are all united into nerve- 

 chains as I have tried to show you, the most logical way of 

 considering the sympathetic system is to treat of it as a por- 

 tion of the entire nervous system, this being looked upon as a 

 unit. This I hope to do in these lectures. 



The results I wish to bring before you are in a large meas- 

 ure consequent upon the application of these improved meth- 

 ods — the Golgi and the intra vitam methylen-blue method — 

 which in the hands of many investigators have in this portion 

 of the nervous system, as well as in others, greatly extended 

 our knowledge. 



These results will be taken up under the following heads : 



1. The development of the sympathetic ganglia and 

 nerves. 



2. The shape and structure of a sympathetic neuron, 



(a) cell body and dendrite ; 



(b) neuraxis ; 



(c) the endings of the neuraxis. 



