HERMANN VON HELMHOLTZ 



Briickianus^ in honour of its discoverer. Helmholtz 

 took up the matter at this point, and made the happy 

 suggestion, which is now universally accepted as the 

 true explanation, that in accommodation the fibres 

 of the ciliary muscle contract and tend to draw the 

 ciliary processes of the choroid forward. Passing in 

 close proximity to these processes, and connected with 

 them, is a thin transparent membrane, the hyaloid 

 membrane, which lines the posterior chamber of the 

 eye. Anteriorly this membrane divides into two 

 layers, one passing before and the other behind the 

 lens, forming what is termed its capsule. The lens 

 is thus bound down, as it were, by its capsule, more 

 especially by the portion of it passing over its anterior 

 surface. When, then, the ciliary processes are pulled 

 forward by the ciliary muscle, the tension of the layer 

 of the capsule in front of the lens is diminished, and 

 the anterior surface of the lens bulges forward by its 

 elasticity. There are certain circular fibres of the 

 ciliary muscle that also assist in this beautiful 

 mechanism. When the eye is again directed to a 

 distant object, the fibres of the ciliary muscle relax, 

 and the lens is flattened by the pressure of the 

 capsule. 



Finally, and to complete the demonstration, Helm- 

 holtz showed, that to accomplish accommodation, no 

 other change in the eye is necessary, and he described 

 an imaginary or schematic eye, slightly differing from 

 the eye of Listing, and for this eye he calculated the 



