SENSE OF SIGHT. 



437 



vitreous humor and also the crystalline lens; the latter 

 becomes flattened by the resistance offered to it by the 

 aqueous humor, or else becomes more convex at the centre 

 of its anterior surface, whilst the iris opposes a deformation 





of the peripheral part to which it is attached. It is possible, 

 on the other hand, that the circular fibres, in contracting, 

 press, by means of the ciliary process, on the circumference 

 of the crystalline lens, which in this sense gives way ; yet, 

 owing to its great elasticity, its thickness at the same time 



