DIOPTRICS OF THE EYE. 



305 



form radial bundles stretching from the ciliary border of the iris 

 toward the pupillary orifice.* Both of these muscles are supplied 

 by autonomic nerve fibers that is, the motor nerve path comprises 

 a preganglionic fiber, arising from the central nervous system, 

 and a postganglionic fiber, arising from a sympathetic ganglion. 

 Anatomically it can be shown that the sphincter muscle is supplied 

 by the short ciliary nerves arising from the ciliary ganglion, 

 which supply also the * 

 muscle of accommoda- 

 tion, the ciliary muscle; 

 while the dilator muscle 

 is supplied by the long 

 ciliary nerves that arise 

 from the ophthalmic 

 branch of the fifth cra- 

 nial nerve, as represented 

 in Fig. 128. The entire 

 course of the motor 

 paths, preganglionic and 

 postganglionic fibers, is 

 represented diagrammat- 

 ically in Fig. 129. The 

 motor fibers to the ciliary 

 muscle and sphincter 

 pupillae arise in the mid- 

 brain in the nucleus of 

 origin of the third cranial 

 nerve, and indeed in a 

 special part of this nu- 

 cleus lying most ante- 

 riorly. They leave the 

 third nerve in the orbit 

 and end within the sub- 

 stance of the ciliarj- gan- 



lc 



Course of constrictor nerve fibers, 

 Course of dilator nerve fibers,- - 



Fig. 128. Diagrammatic representation of the 



nerves governing the pupil (after Foster) : II, Optic 

 gJlOn, Whence the path nerve; c.g, ciliary ganglion; r.b, its short root from 

 , -II *"i motor ocuh nerve; sum its svmDathetic root* rl 



IS Continued by Sympa- its long root from V, ipthkl<5SS Branch ofoph- 

 thpflP fnnto-p no-linn I'M "lalmic division of fifth nerve; s.c, short ciliary 

 V P Ob LgdJlgllOniC ; nerves; l.c, long ciliary nerves. 



fibers emerging from the 



ganglion in the short ciliary nerves. The fibers to the dilator 

 muscle have a very different path. They arise also in the brain, 

 most probably in the midbrain, although their exact origin has 

 not been determined satisfactorily, and pass down the spinal 



*For a physiological proof and the literature of the controversy see 

 Langley and Anderson, "Journal of Physiology/' 13, 554, 1892. For the 

 histological proof, Grunert, "Archives of Ophthalmology/' 30, 377, 1901. 

 20 



