THE SENSES 



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(Figs. 382, 383). This covers the choroid as a delicate membrane, 

 extending to the ciliary processes, where it ends in a toothed margin, 

 the ora serrata. The optic nerve forms a kind of stalk to which the 

 eyeball is attached. Its point of entrance at the optic disc is a little 

 nearer the median line than the a ntero- posterior axis, which nearly 

 passes through the centre of a small depression, the fovea centralis, 

 situated in the middle of the macula lutea, or yellow spot. From 

 the optic disc (sometimes called the optic papilla) the optic nerve 



FIG. 382. THE RETINA. 



Rods. 



Cones. 



OF 



FIG. 383' DIAGRAM OF STRUCTURE 



RETINA (AFTER CAJAL). 

 Figs. 3^2, 383. -i, internal limiting mem- 

 brane ; 2, H, layer of nerve-fibres ; 3, G, 

 layer of ganglion cells ; 4, F, internal 

 molecular layer ; 5, E, internal nuclear 

 layer ; 6, C, external molecular layer ; 7, B, 

 external nuclear layer ; 8, external limiting 

 membrane ; 9, A, layer of rods and cones ; 

 10, pigmented epithelium. 



spreads over the retina as a layer of non-medullated fibres, separated 

 from the interior of the eyeball only by the internal limiting mem- 

 brane. This so-called membrane is formed by the expanded feet 

 of the fibres of Miiller, which run like a scaffolding or framework 

 through nearly the whole thickness of the retina, terminating at the 

 outer limiting membrane. External to the layer of nerve-fibres is 

 the stratum of large ganglion cells, whose axons they are ; next to 

 this the inner molecular layer, or inner synapse layer, made up largely 

 of the branching dendrites of these cells. The fifth layer is the inner 



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