410 STUDIES IN ADVANCED PHYSIOLOGY. 



the body not included in the two other systems. Such 

 ganglia are those of the heart, the plexuses of Auerbach 

 and Meissner in the intestine, the intrinsic ganglia of 

 blood-vessels, the solar plexus of the mesentery, etc. A 

 sharp distinction between these three systems cannot at all 

 be drawn. The spinal nerves are connected with the sym- 

 pathetic nerves, and both these nerves may run into spora- 

 dic ganglia. 



NERVOUS ELEMENTS. 



In studying in detail any of these systems two kinds of 

 nervous structures are at once discernible: 



1. Nerves, Nerve Trunks and Plexuses. By dissect- 

 ing a body one meets almost everywhere whitish looking 

 threads which are nerves. These might easily be mistaken 

 for tendon threads or other connective tissue fibers. If by 

 means of the scalpel the course of such a thread or cord is 

 followed it is soon seen to divide and sub-divide until the 

 finer ramifications are lost among the muscles or glands or 

 in the skin. If the microscope should be called to aid it 

 would be possible to actually see these nerve terminations 

 in many instances, such as their endings in the nerve- 

 plates of the voluntary muscles or in the tactile corpuscles 

 of the skin. If, on the other hand, one should follow the 

 course of such a nerve inward, it would be seen to unite 

 with other nerves, until finally the nerve would be found 

 entering the spinal cord or brain, or at least some central 

 ganglion. Such whitish cords are called nerve trunks. A 

 cross-section of such a nerve trunk would show that it is 

 composed of very many smaller cords, the nerve fibers, and 

 that the trunk is really nothing more than a collection of 

 fibers running in the same direction wrapped in a common 

 envelope of white connective tissue. It is this white con- 

 nective tissue envelope and not the nerve substance itself 

 which gives to the nerve trunk the color in question. Not 

 infrequently by following a nerve trunk it might be seen to 

 send off communicating branches to other nerve trunks, and 



