DIOPTRICS OF THE EYE. 



325 



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 pregangl ionic 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. 135. The entire 

 course of the motor 

 paths, preganglionic 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 

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



1C 



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 oculi nerve; sym., 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. 



* 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. 



