THE SENSES 



107 



C,IM 



The eye may be described as a hollow sphere of fibrous 

 tissue (Fig. 44), the posterior part, the sclerotic (Scl.), being 

 opaque ; the anterior part, the cornea (Cor.), being transparent 

 and forming part of a sphere of smaller diameter than the 

 sclerotic. Inside the sclerotic coat is a loose fibrous layer, 

 the choroid (Chor.), the connective tissue cells of which are 

 loaded with melanin, a black pigment. This is the vascular 

 coat of the eye the larger 

 vessels running in its outer 

 part, and the capillaries in its 

 inner layer. Anteriorly, just 

 behind the junction of the 

 cornea and sclerotic, it is 

 thickened and raised in a 

 number of ridges, the ciliary 

 processes (Oil. J/.), running from 

 behind forward and termi- 

 nating abruptly in front. In 

 these the ciliary muscle is 

 situated. It consists of two 



Sets of non-Striped muscular FIG. 44. Horizontal section through the 



fibres first, radiating fibres, 

 which take origin from the 

 sclerotic just behind the corneo- 

 sclerotic junction, and run 

 backwards and outwards to be 

 inserted with the bases of the 

 ciliary processes; second, circu- 

 lar fibres which run round the processes just inside the 

 radiating fibres. The choroid is continued forward in front 

 of the ciliary processes to the pupil as the iris, and in it are 

 also two sets of non-striped muscular fibres first, the circular 

 fibres, a well-marked band running round the pupil, and 

 called the sphincter pupilLv (Sph. P.) muscle ; second, a less 

 well-marked set of radiating fibres, which are absent in 

 some animals, and which constitute the dilator pupillte 

 muscle (D.P.). 



That part of the eye in front of the iris is filled by a 

 lymph-like fluid, the aqueous humour, while the part behind 

 is occupied by a fine jelly-like mucoid tissue, the vitreous 



Left Eye. Cor. .cornea ; Scl. , sclerotic ; 

 0[>t. N., optic nerve ; Chor. , choroid ; 

 CiL M., ciliary processes with ciliary 

 muscle ; D. P. .dilator pupillse muscle ; 

 Sph. P. , sphincter pupillse muscle ; 

 L. , crystalline lens; S.L., hyaloid 

 membrane forming suspensory liga- 

 ment and capsule of lens. Ret., 

 retina. 



