50 SPECIAL SENSES. 



Ciliary Muscle. This muscle, formerly known as the 

 ciliary ligament, and now sometimes called the tensor of the 

 choroid, is almost universally recognized by physiologists as 

 the agent for the accommodation of the eye to vision at dif- 

 ferent 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. For this reason, 

 we shall describe its arrangement as exactly as possible. 



The form and situation of the ciliary muscle are as fol- 

 lows : It surrounds the anterior margin of the choroid, in the 

 form of a ring about -|- of an inch wide and ^ of an inch in 

 thickness at its thickest portion, 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 semitransparent and of a grayish color. Its 

 situation is just outside of the ciliary processes, these pro- 

 cesses projecting in front of its anterior border about -% of 

 an inch. 



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 pectinatum. Its fibres, which are chiefly longitudinal, 

 pass backward and are lost in the choroid, extending some- 

 what farther back than the anterior limit of the retina. In 

 addition, a net-work of circular muscular fibres has been de- 

 scribed lying over the anterior portion of the ciliary body, at 

 the periphery of the iris, beneath the longitudinal fibres ; but 

 these are regarded by Donders as simple continuations of the 

 innermost layers of the longitudinal fibres, which gradu- 

 ally assume a circular direction, not meriting description as a 

 separate muscle. 1 Some of these fibres have an oblique di- 

 rection. 



1 BONDERS, On the Anomalies of Accommodation and Refraction of the Eye^ 

 The New Sydenham Society, London, 1864, p. 25. 



