CHAPTER VII. 

 THE SYMPATHETIC SYSTEM. 



THE sympathetic nerves, as compared with those of the cerebro- 

 spinal system, have certain peculiarities of arrangement and dis- 

 tribution. The double nervous cord running through the great cavi- 

 ties of the body, the numerous and scattered ganglia, united with 

 each other by slender filaments, the frequent plexiform arrangement of 

 the branches, and their distribution to the organs of circulation and 

 nutrition, form a well-marked group of anatomical features. But not- 

 withstanding the general importance of these characters, the sympa- 

 thetic nerves and ganglia do not constitute an independent nervous 

 system. Neither their anatomical elements nor their external connec- 

 tions are essentially different from those of the cerebro-spinal nerves 

 and centres. The sympathetic trunks and branches contain medullated 

 nerve fibres like those of the spinal nerves ; and its ganglia contain 

 nerve cells with prolongations in the form of axis cylinders. The main 

 peculiarity of the sympathetic nerve fibres is that they are, as a rule, 

 of small diameter, though not smaller than the average of those in the 

 cerebro-spinal nerves. The cells of the sympathetic are also generally 

 small, never, according to Kolliker, equalling the largest of those in 

 the spinal cord or the brain ; and they are also characterized by the 

 frequency with which they send out a single prolongation, becoming 

 apparently the source of new fibres. 



On the other hand, the posterior roots of the spinal nerves are pro- 

 vided with ganglia similar to those of the sympathetic system. The 

 same arrangement exists in some of the cranial nerves, as in the pneu- 

 mogastric, glossopharyngeal, and the fifth pair. Thus all the sensitive 

 and mixed cerebro-spinal nerves contain fibres of ganglionic origin, in 

 addition to those from the brain and spinal cord. Furthermore, all the 

 sympathetic ganglia receive filaments from the cerebro-spinal nerves, 

 the fibres of which, there is reason to believe, pass through the ganglion 

 to the peripheral branches of the sympathetic system. This is inferred 

 from the fact that many of these fibres cannot be seen either to origin- 

 ate or terminate in the ganglion, and also from the paralyzing effect 

 produced on a muscular organ supplied with sympathetic fibres, by 

 division of the cerebro-spinal nerve which communicates with its 

 ganglion. This is especially shown by dilatation of the pupil follow- 

 ing division of the oculomotorius nerve, which supplies the iris with 

 a motor branch through the ophthalmic ganglion. The numerous 

 filaments supplied by the pneumogastric nerve to the cardiac branches 



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