THE BRAIN 121 



to the skeletal muscles are represented by continuous 

 fibers spanning the interval. In the autonomic system 

 the case is otherwise. Fibers which issue from the brain 

 and cord, bearing impulses destined to take effect in 

 structures other than skeletal muscles, do not actually 

 extend to these terminal stations. They end by synapses 

 against nerve cells of a second order which in their turn 

 control the effectors in question. These distributing 

 neurons usually have their cell-bodies in various ganglia 

 which are found in many localities. The fibers which 

 run from the central nervous system to the way-stations 

 are called pre-ganglionic, those which relay the impulses 

 to the end-organs are called post-ganglionic. It appears 

 to be the rule that one pre-ganglionic neuron stands in 

 relation to a number of those of the dependent rank. 

 It seems to follow that impulses sent from the brain and 

 the cord to the ganglia are there multiplied and diffused. 

 There can hardly be the precise localizing of effect 

 obtainable in the command of skeletal muscles. 



The pre-ganglionic fibers proceeding from the spinal 

 cord are for the most part connected with ganglia which 

 are placed in two long chains to the right and left of the 

 spinal column at the back of the body cavity. These 

 two chains of ganglia with their associated axons have 

 been known as the sympathetic system. The term is 

 an odd one and is not to be given any tinge of the 

 psychologic significance naturally coupled with it. 



The functions of the autonomic system may be sum- 

 marized under three divisions: First we have those of 

 the head or cranial section. Fibers originating here 

 produce effects in many organs of the trunk as well as 

 in the head. They can bring about contraction of the 

 pupil, increase of curvature of the crystalline lens, 

 changes in the circulation in the glands and skin of the 

 head, secretion of saliva, and slowing of the heart. 

 They also contract the bronchral tubes, cause the secre- 

 tion of gastric juice, and reinforce the muscular activity 

 of most of the alimentary canal. 



