DIOPTRICS OF THE EYE. 



321 



of the dilator pupillae is much less distinct. For a long time its 

 existence was the subject of controversy, but it is now conceded 

 that such a muscle is present in the form of a layer of elongated 

 spindle-like cells which lie close to the pigment layer of the iris and 

 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 ciUary ganglion, 

 which supply also the 

 muscle of accommoda- 

 tion, the ciliary muscle; 

 while the dilator muscle 

 is suppUed by the long 

 cihary nerves that arise 

 from the ophthalmic 

 branch of the fifth cra- 

 nial nerve, as represented 

 in Fig. 135. The entire 

 course of the motor 

 paths, pregangUonic and 

 postganglionic fibers, is 

 represented diagrammat- 

 ically in Fig. 136. The 

 motor fibers to the ciliary 

 muscle and sphincter 

 pupillse 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 ciliary gan- 

 glion, whence the path 

 is continued by sympa- 

 thetic ( postganglionic ) 

 fibers emerging from the 

 i^anglion in the short ciliary nerves. The fibers to the dilator 



* 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. 

 21 



Course of constrictor nerve fibers. 

 Course of dilator nerve fibers,- - 



Fig. 135. — Diagrammatic representation of the 

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

 nerve; e.g, ciliary ganglion; r.b, its short root from 

 ///, motor ocuh nerve ; si/m., its sympathetic root; rl, 

 its long root from V, ophthalmonasal branch of oph- 

 thalmic division of fifth nerve; s.c, short ciliary 

 nerves; l.c, long ciliary nerves. 



