VI 



DIOPTKIC MECHANISM OF THE EYE 273 



anatomical details are seen, as well as the relative thickness of 

 the three principal coats of the eye and the optic nerve as it 



enters it (Fig. Ill, -5). 



The interior of the eyeball contains the vitreous body, 

 crystalline lens, and aqueous humour. The vitreous body takes 

 up four-fifths of the eyeball. It is quite transparent, gelatinous 

 in consistency, sub-globular in shape, with a depression in front 

 to receive the lens and its capsule (fossa patellaris). At ^ the 

 periphery the whole vitreous body is covered with a delicate 



. 112. Fibrous structure of adult lens. 1, anterior; 2, posterior; 3, lateral view. f. (Arnold.) 

 In 3, a., anterior; p., posterior pole. The direction of the superficial fibres is indicated by the 

 curved lines. 



membrane, the hyaloid membrane. In the adult this has no 

 vessels, and its nutrition is dependent on the surrounding vessels 

 of the retina and ciliary processes. 



The crystalline lens is an elastic transparent body of bi-convex 

 form and rounded circumference, enclosed in an elastic membrane 

 known as the capsule of the lens. Its anterior surface, which is 

 in contact with the iris, represents a segment of a circle with a 

 longer radius or curvature than that of the posterior surface, 

 which rests upon the fossa patellaris of the vitreous body. The 

 refractive power of the crystalline substance is greater than that 

 of water, and increases from the periphery of the lens to its 



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