CRYSTALLINE LENS 



66 1 



Crystalline Lens. The crystalline is a double-convex lens, which is 

 transparent and very elastic. Its action in the refraction of the rays 

 of light is analogous to that of convex lenses in optical instruments. It 

 is situated behind the pupil in what is called the hyaloid fossa of the 

 vitreous humor, which is exactly moulded to its posterior convexity. 

 In the foetus the capsule of the lens receives a branch from the arteria 

 centralis, but it is non-vascular in the adult. The anterior convexity 

 of the lens is just behind the iris, and its borders are in relation with 

 what is known as the suspensory ligament. The convexities do not 

 present regular curvatures, and they are so subject to variations after 

 death that measurements, post mortem, are of little value. During life, 



Fig. 170. Crystalline lens, anterior view 

 (Babuchin). 



Fig. 171. Section of the crystalline 

 lens (Babuchin). 



however, they have been exactly measured in different conditions of ac- 

 commodation. The diameters of the lens in the adult are about 1 of 



o 



an inch (8.5 millimeters) transversely and \ of an inch (6.4 millimeters ) 

 antero-posteriorly. The convexity is greater on its posterior than on 

 its anterior surface. In foetal life the convexities of the lens are greater 

 than in the adult and its structure is much softer. In old age the con- 

 vexities are diminished and the lens becomes harder and less elastic. 

 The substance of the lens is made up of layers of fibres of different 

 degrees of density, and the whole is enveloped in a delicate membrane 

 called the capsule. 



The capsule of the lens is a thin transparent membrane and is very 

 elastic. It usually is from 25*00" to TsVo" ^ an mcn ( IO to l 7f JL ) 



