THE EYE 1513 



Anteriorly they are related to the posterior chamber of the eyeball 

 at its circumference. Posteriorly they rest upon the zonule of 

 Zinn, the folds of which fit closely in between them. 



Structure. — The ciliary processes are similar in structure to the 

 choroid, but the pigment-cells are not so numerous. On their 

 deep or posterior surfaces the processes are covered by the pars 

 ciiiaris retinaB, which is prolonged from the pigmentary layer of 

 the retina, and is continuous with the pars iridica retinae (uvea) on 

 the posterior surface of the iris. 



The arteries of the ciliary processes are derived from those of the 

 anterior part of the choroid, and from the anterior ciliary arteries. 

 The veins pass to those of the choroid. 



Ciliary Muscle. — ^This muscle is composed of unstriped fibres. 

 It forms a greyish-white ring, about ^ inch broad, which is 



Pupil 



Iris (dilator pOTtiao) 



Seven Ciliary Processes '''^^^;^^^^^5:>^^ ^n Ciliary Process 

 reflected 



Fig. 628. — The Iris and Ciliary Processes (Posterior View) 



(HiRSCHFELD AXD LeVEILL^). 



situated at the anterior part of the choroid, opposite the ciliary 

 processes. The fibres are arranged in two sets — radial and circular. 

 The radial fibres arise from the deep surface of the sclerotic, close 

 to the comeo-scleral junction, and behind the canal of Schlemm. 

 From this origin they pass backwards in a radiating manner, and 

 are inserted into the orbicularis ciiiaris and the attached ends of 

 the ciliary processes. The circular fibres form a ring around the 

 circumference of the iris, internal to the radial fibres. 



The ciliary muscle is supplied by the ciliary nerves, which are 

 branches of the ciliary ganglion. 



Action. — The ciliary muscle is the muscle of accommodation, and 

 adjusts the eye to the vision of near objects. When it contracts it 

 draws forwards the choroid and the ciliary processes ; the suspensory 

 ligament of the crystalline lens is thereby relaxed ; and, as a 

 consequence, the anterior surface of the lens is rendered convex. 



