CILIARY MUSCLE AND IRIS. 



795 



By their free extremities the processes bound peripherally the 

 space (posterior chamber; fig. 291, i t p. 796) behind the iris; in 

 front, they correspond to the ciliary muscle, and at their inner ends 

 to the back of the iris ; while behind, they are closely applied to 

 the membrane on the front of the vitreous body (suspensory 

 ligament of the lens ; fig. 291, t), and fit into hollows between 

 eminences on the anterior surface of that structure. 



Structure. The choroid coat and its ciliary processes are composed 



blood \v els supported by pigmented areolar tissue. Most 

 externally is a delicate stratum of connective tissue known as the 

 lamina suprachoroidea, similar to the membrana fusca of the sclerotic, 

 to which it is connected ; next 

 to this is a layer containing 

 the larger ramifications of the 

 arteries and veins ; and in the 

 deepest part the vessels form 

 a very fine and close capillary 

 network (tunica Ruyschiana). 

 In the ciliary processes the 

 meshes of the capillary net- 

 work are larger, and the inter- 

 stitial pigment disappears to- 

 wards the free ends of the 

 larger proo 



CILIARY MUSCLE (fig. 289, 

 d, e). In the eye from which 

 the sclerotic coat has been re- 

 moved, the white ring of the 

 ciliary muscle may be seen 

 covering the front of the 

 choroid coat. 



The muscle forms a circular 

 band, of a greyish white colour, 

 and about one-tenth of an inch 

 wide, on the surface of the 

 choroid coat close to the outer 

 margin of the iris. It consists 

 of imstriated fibres, which are in two sets, radiating and circular : 



The radiating fibres (fig. 291, ) arise in front from the sclerotic 

 oat close to the junction with the cornea (beneath r), and are 

 directed backwards, spreading out, to be inserted into the choroid 

 coat opposite to, and a little behind, the ciliary processes. Some of 

 the deeper fibres become transverse, and pass gradually into the 

 following set. 



The circular fibres are beneath the radiating, and form a narrow 

 bundle (fig. 291, m) surrounding the edge of the iris, opposite the 

 inner part of the ciliary processes. 



Action. The ciliary muscle draws forwards the fore part of the 

 choroid coat and the ciliary processes, and relaxes the suspensory 

 ligament of the lens, thereby allowing the lens to Income more 



relations 



structure of 

 



layer, 



Ciliary 

 muscle : 



FIG. 290. POSTERIOR VIEW OF THE 

 FORE PART OP THE CHOROID COAT 

 WITH ITS CILIARY PROCESSES, AND 

 THE BACK OF THE IRIS. 



a. Anterior piece of the choroid 

 coat. 



b. Ciliary processes. 



c. Iris. 



d. Sphincter of the pupil. 



e. Bundles of fibres of the dilator 

 of the pupil, represented diagram- 

 matically. 



position ; 



and circular 

 fibres; 



