480 



Mr. W. H. Jessop. 



[June 10. 



partial dilatation of the iris, and the pupil is inactive to light or 

 accommodation. 



ft. Stimulation of the path taken by the mydriatic nerve, as 

 described in the anatomical division, gives rise to mydriasis. Sec- 

 tion of the nerve in any part of its course is followed by contrac- 

 tion of the pupil, but never excessive ; the myosis is increased a little 

 the higher up and the nearer the eyeball the section is made, arid this 

 is due to the tonic action of the ganglia. 



The mydriatic fibres accompanying the sympathetic therefore find 

 their way by the long ciliary nerves to the eyeball ; this may, as the 

 rest of their course, be proved by division of them all, when irritation 

 of the cervical sympathetic gives rise to no alteration in the pupil. 



I found on stimulating a single long ciliary nerve that, if the pupil 

 was dilated to start with, general increase in the mydriasis occurred. 

 If, however, the pupil were partially contracted by pilocarpin only 

 half the pupil responded, and if the pupil were more contracted only 

 one-quarter dilated. 



In birds stimulation of the cervical sympathetic has no effect on 

 the pupil. 



Dual Nature. — The cervical sympathetic containing vaso-constrictor 

 nerves for the head and neck, it is necessary to show that the dilata- 

 tion of the pupil is not a purely vascular act. 



This is shown by — 



1. Bleeding an animal to death, and then on exciting the cervical 

 sympathetic several times total mydriasis still occurs. 



2. Mydriasis on stimulation of the cervical sympathetic precedes 

 the contraction of the carotid vessels. 



3. The maximum dilatation is reached before the carotid vessels 

 are completely constricted. 



4. The carotid vessels are constricted when the pupil begins to 

 contract again. 



5. The pupil is dilated a short time, while the carotid vessels are 

 constricted for a longer time. 



6. The pupil is again constricted before completion of relaxation 



of the vessels. 



7. Section of the trigeminus in front or behind the Grasserian 

 ganglion gives rise to myosis which soon passes off. 



Stimulation of the trigeminus generally gives rise to myosis, 

 which is probably reflex, as on section of the third nerve, I obtained 

 an increase to the mydriasis by stimulating it, as also Fr. Franck has 

 done. 



Balogh and others also attribute a mydriatic function to the 

 trigeminus. 



(2.) B. The nerves supplying the ciliary muscle are the (<x) third 

 and (/3) the long ciliary branches of the nasal. 



