PHYSIOLOGICAL ANATOMY OF THE EYEBALL 653 



regular alternation, between the larger. Within the folds, are received 

 corresponding folds of the thick membrane, continuous anteriorly with 

 the hyaloid membrane of the vitreous humor, called the zone of Zinn. 



The ciliary processes present bloodvessels, which are somewhat 

 larger than those of the rest of the choroid. The pigmentary cells are 

 smaller and are arranged in several layers. The anterior border of 

 the processes is free and contains little or no pigment. 



Ciliary Muscle. This muscle, formerly known as the ciliary liga- 

 ment and now sometimes called the tensor of the choroid, is the agent 

 for the accommodation of the eye to vision at different distances. Under 

 this view, the ciliary muscle is an organ 

 of great importance ; and it is essential, 

 in the study of accommodation, to have 

 an exact idea of its relations to the coats 

 of the eye and to the crystalline lens. 



The form and situation of the ciliary 

 muscle are as follows : It surrounds the 

 anterior margin of the choroid, in the 

 form of a ring about \ of an inch (3.2 

 millimeters) wide and -$ of an inch (0.5 

 millimeter) in thickness at its thickest 

 portion, which is its anterior border. It Fig * l67 ' " CUimy muscle ' x 5 (Sappey)< 



i, I, crystalline lens; 2, hyaloid mem- 

 beCOmeS thinner from before backward, brane; 3, zone of Zinn; 4, iris; 5, 5, one of 



until its posterior border apparently * e u ciliar y P rocesses = 6 - 6 - radiating fibres 



* 'of the ciliary muscle ; 7, section of the cir- 



f 11565 with the fibrOUS Structure Of the cular portion of the ciliary muscle; 8, venous 



choroid. It is semitransparent and of &f?'^3^ 



a grayish Color. ItS Situation is jUSt th e cornea; 14, membrane of Descemet; 



, . i r , i .,. , 1=5, ligamentum iridis pectinatum ; 16, epi- 



OUtSlde Of the Ciliary processes, these th ' eliu 8 m of the mem brane of Descemet; 



processes projecting in front of its an- J 7. union of the sclerotic coat with the 



, . cornea; 18, section of the canal of Schlemm. 



tenor border, about ^ of an inch ( i mil- 

 limeter). 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, the border of the membrane 

 of Descemet, and the ligamentum iridis pectinatum. Its fibres, which 

 are chiefly longitudinal, pass backward and are lost in the choroid, ex- 

 tending somewhat farther back than the anterior limit of the retina. 

 In addition, a network 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. 



