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THE RETINA. 



The retina is very complicated in its structure. No less 

 than eight layers have been distinguished, as shown in Fig. 

 90. Of these layers the outermost, the layer of the rods 

 and cones, is the one directly concerned in appreciating the 

 differences in the vibrations of the light. 



The rays of light pass through the retina, and produce 

 their effect on the rods and cones which constitute the outer 



Inner or Vitreous Surface 



I 



Internal Limiting Layer 



Layer of Nerve Fibers 

 Layer of Nerve Cells 



Inner Molecular Layer 



Inner Nuclear Layer 



Outer Molecular Layer 



Outer Nuclear Layer 

 External Limiting Layer 

 Layer of Rods and Cones 



Layer of Pigment Cells 



Outer or Choroid Surface 



Fig. 90. Diagrammatic Section of the Human Retina. 



(back) layer ; and the nerve impulses aroused by the light 

 must return through the thickness of the retina to be conveyed 

 along the nerve fibers of the innermost layer of the retina to 

 the optic nerve. 



The Center of Distinct Vision. Near the middle of 

 the back part of the retina is the Yellow Spot (macula lutea) t 



