812 



THE EYE AND VISION 



[CH. LVIII. 



The choroid coat ends in front in what are called the ciliary 

 processes (figs. 509, 510). These consist of from 70 to 80 meridion- 

 ally arranged radiating plaits, which consist of blood-vessels, fibrous 

 connective tissue, and pigment corpuscles. They are lined by a 



continuation of the membrane of Bruch. 

 The ciliary processes terminate at the 

 margin of the lens. The ciliary muscle 

 (13, 14, and 15, fig. 509), takes origin at 

 the corneo-scleral junction. It is a ring 

 of muscle, 3 mm. broad and 8 mm. thick, 

 made up of fibres running in three direc- 

 tions, (a) Meridional fibres near the 

 sclerotic and passing to the choroid ; 

 (5) radial fibres inserted into the choroid 

 behind the ciliary processes ; and (c) cir- 

 cular fibres (muscle of Muller), more 

 internal ; they constitute a sphincter. 



The Iris is a continuation of the 

 choroid inwards beyond the ciliary pro- 

 cesses. It is a fibro-muscular membrane 

 perforated by a central aperture, the pupil. 

 Posteriorly is a layer of pigment cells 

 (uvea), which is a continuation forwards 

 of the pigment layer of the retina. The 

 iris proper is made of connective tissue 

 in front with corpuscles which may or 

 may not be pigmented, and behind of 

 similar tissue supporting blood-vessels. 

 The pigment cells are usually well 

 developed here, as are also many nerve- 

 fibres radiating towards the pupil. Sur- 

 rounding the pupil is a layer of circular 

 unstriped muscle, the sphincter pupillce. 

 In some animals there are also muscle- 

 fibres which radiate from the sphincter 

 in the substance of the iris forming the 

 dilator pupillce. The iris is covered an- 

 teriorly by a layer of epithelium con- 

 tinued upon it from the posterior surface 

 of the cornea. 



The Lens is situated behind the iris, being enclosed in a distinct 

 capsule, the posterior layer of which is not so thick as the anterior. 

 It is supported in place by the- suspensory ligament, fused to the 

 anterior surface of the capsule. The suspensory ligament is derived 

 from the hyaloid membrane, which encloses the vitreous humour. 



FIQ. 508. Vertical section of rabbit's 

 cornea, stained with gold chloride. 

 e, Stratified anterior epithelium. 

 Immediately beneath this is the 

 anterior homogeneous lamina of 

 Bowman, n, Nerves forming a 

 delicate sub-epithelial plexus, and 

 sending up fine twigs between the 

 epithelial cells to end in a second 

 plexus on the free surface; d, 

 Descemet's membrane, consisting 

 of a fine elastic layer, and a single 

 layer of epithelial cells; the sub- 

 stance of the cornea, /, is seen to 

 be fibrillated, and contains many 

 layers of branched corpuscles, ar- 

 ranged parallel to the free surface, 

 and here seen edgewise. 



(Schofield.) 



