ii8 Journal of Comparative Neurology. 



off from this ganglion. It has further been shown (Langley 

 and others), that the same physiological effects may be pro- 

 duced on stimulating the upper thoracic nerves in the vertebral 

 canal. To be more explicit and to follow Langley's (78) ac- 

 count, we find that " the pupil receives dilator fibers from the 

 1st, Ilnd, Ilird thoracic nerves. The relative effect of these 

 nerves varies somewhat in different animals of the same species, 

 and varies considerably in animals of dift'erent species." "In 

 the dog and cat the 1st, Ilnd, Ilird, IVth and sometimes also 

 the Vth thoracic nerves, contain vaso-motor fibers for the head, 

 while in the rabbit the Ilnd to the Vllth thoracic nerves carry 

 such fibers." In the dog and cat Langley found that "the sec- 

 ond thoracic nerve carried the greatest number of the fibers 

 which on stimulation cause a secretion of the submaxillary 

 gland ; although the Ilird, IVth and Vth (the latter in the cat) 

 carried such fibers." From these results we learn that an im- 

 pulse, which leaves the spinal cord through the upper thoracic 

 nerves, is carried along nerve fibers in the cervical sympathetic 

 to the superior cervical ganglion, and from there to the head 

 (vaso-motor); to the eye (pupil dilators) ; and to the submaxil- 

 lary gland (secretory). 



This question may now be asked. What relation do the 

 small medullated fibers which leave the spinal cord through the 

 anterior roots and pass through the white rami to the sympa- 

 thetic ganglia and which, as has been shown, on stimulation 

 cause physiological effects similar to those obtained when the 

 ganglia or their nervous branches are directly stimulated hold 

 to the sympathetic nerve cells of the ganglia ? Do they pass 

 through the ganglia, or do they end therein ? 



The physiologists have aided very materially in the solu- 

 tion of this problem, and of their number, especial credit must 

 be given to Professor Langley, who through his untiring search 

 and wonderfully exact work has done so much to give us a bet- 

 ter understanding of the physiology of the sympathetic system. 



The work to which I wish especially to refer at this point 

 is the following : 



Langley and Dickinson (80-81) have shown that "after 



