THE AUTONOMIC NERVOUS SYSTEM 895 



on each side. Because they have certain characteristics in common these 

 two outflows are classed together as the bubo-sacral (sometimes called 

 the parasympathetic) division of the autonomic nervous system. The 

 thoracico -lumbar outflow consists of connector fibers leaving the cord 

 between the first thoracic and second or third lumbar segment. This out- 

 flow is sometimes called the sympathetic division of the autonomic 

 nervous system. 



The terminology applied to these systems is confusing because of the 

 different usage of the same name by different authors. The following 

 table indicates the classification adopted in this book, together with the 

 synonymous terms in current use. 



While the details of the anatomical courses of the fibers to the great 

 variety of structures innervated by the autonomic system is beyond 

 the scope of a textbook of physiology, it is appropriate to outline certain 

 generalities concerning the arrangement of the connector and effector 

 neurons which supply different organs. In addition to the obvious meth- 

 ods for tracing the paths of nerve fibers by degeneration and by stimu- 

 lating the roots of the motor nerves knowledge of the course of the 

 connector neurons has been gained by the use of a special method dis- 

 covered by Langley. This depends upon the fact that nicotine in cer- 

 tain concentrations specifically blocks the passage of nerve impulses 

 across the synapse between the connector fiber and the effector neuron 

 without disturbing conduction in the course of nerve fibers unin- 

 terrupted by a synapse. Consequently when nicotine is painted upon an 

 outlying ganglion it is possible to determine, by stimulating the con- 

 nector fibers, whether they pass through the ganglion without inter- 

 ruption or not. In this way it has been learned that the motor paths in 

 the autonomic system fall into three groups with regard to the position 

 of the synapse between the connector and the outlying neuron. 



Position of the Effector Neuron. The outlying neuron lies wholly 

 in the walls of the organs innervated by the vagus nerve, the sacral 

 outflow, and that part of the thoracico-lumbar outflow which supplies the 

 organs which have developed from the Wolfian and Mullerian ducts, 

 i. e., the ureters, uterus, and vas deferens. The cells of Auerbach's 

 plexus in the gastrointestinal tract represent outlying neurons from 



