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THE NERVOUS SYSTEM 



pigmented layer behind, continuous with the retina. In 

 the middle layer are two muscles — sphincter pupillse, whose 

 fibres are arranged circularly, and the dilator, whose fibres 



Fig. 4r). — Transverse section through equator of left eye seen from 

 above (from Starling's Principles of Physiology). 



are arranged radially. Immediately behind the iris is the 

 lens, biconvex in shape and having a high refractive index. 

 It is supported by and enclosed in the suspensory ligaments. 

 It divides the eyeball into two compartments, anterior and 

 posterior. The anterior chamber is occupied by the fluid 



