678 



SPECIAL SENSES. 



the anterior margin of the choroid, in the form of a ring about -J of an inch 

 (3*2 mm.) wide and ^ of an inch (0-5 mm.) in thickness at its thickest por- 



FIG. 245. Ciliary muscle ; magnified 10 diameters (Sappey). 



1, 1, crystalline lens ; 2, hyaloid membrane ; 3, zone of Zinn ; 4, iris ; 5. 5, one of the ciliary processes ; 

 6, 6, radiating fibres of the ciliary muscle ; 7, section of the circular portion of the ciliary muscle ; 

 8, venous plexus of the ciliary process ; 9, 10, sclerotic coat ; 11, 12, cornea ; 13, epithelial layer of 

 the cornea ; 14, membrane of Descemet ; 15, ligamentum iridis pectinatum ; 16, epithelium of the 

 membrane of Descemet ; 17, union of the sclerotic coat with the cornea ; 18, section of the canal of 

 Schlemm. 



tion, which is its anterior border. It becomes thinner from before backward, 

 until its posterior border apparently fuses with the fibrous structure of the 

 choroid. It is semi-transparent and of a grayish color. Its situation is just 

 outside of the ciliary processes, these processes projecting in front of its 

 anterior border, about ^ of an inch (1 mm.). Regarding the anterior border 

 of this muscle as its origin and the posterior border as its insertion, it arises 

 in front, from the circular line of junction of the cornea and sclerotic, from 

 the border of the membrane of Descemet, and the ligamentum iridis pecti- 

 natum. Its fibres, which are chiefly longitudinal, pass backward and are lost 

 in the choroid, extending somewhat farther back than the anterior limit of 

 the retina. In addition a net-work of circular muscular fibres has been 

 described, lying over the anterior portion of the ciliary body, at the periphery 

 of the iris, beneath the longitudinal fibres. Some of these fibres have an 

 oblique direction. 



The ciliary muscle is composed mainly of muscular fibres. These fibres, 

 anatomically considered, belong to the non-striated variety. They are pale, 

 present a number of oval, longitudinal nuclei, and have no striae. 



