NERVOUS CONSTITUENTS OF THE EETINA. 257 



optic-nerve layer, whilst the remainder run peripherically into 

 the internal granulated layer, where they become exceedingly 

 attenuated by division. The nature and course of the fine gan- 

 glion-cell processes of the internal granulated layer resemble 

 in every respect those of the finest primitive nerve fibrils of the 

 grey substance of the cortex of the cerebrum. During their 

 intricate course they form an extremely close-meshed plexus, and 

 lie imbedded in the tenacious spongy connective tissue, which 

 prevents their isolation for any considerable distance. There 

 is consequently but little prospect that the communication of 

 these ganglion-cell processes with the nervous fibres of the fol- 

 lowing layers will ever be demonstrated. In the layer of the 

 inner granules, nerve fibres are found running perpendicularly 

 to the surface of the retina. But at the macula lutea there are 

 also oblique fibres. Each of these fibres is interrupted by a 

 small cell, an internal granule, or a bipolar ganglion cell, the 

 central process of which (that part of the radial nerve fibre 

 which ascends from the internal granulated layer) is very deli- 

 cate, whilst the peripheric is thick. This probably always 

 loses itself by branching in the external granulated layer, which 

 resembles the internal, and permits as little as the former the 

 course of the fine nerve fibrils that pass through it to be exactly 

 followed. From it the rods and cones arise, standing perpen- 

 dicularly to its surface, except at the macula lutea, where they 

 are oblique. The cone fibres arise by the coalescence of a great 

 number of fine fibrils, each forming a large fasciculus of such 

 fibrils, which resembles a thick fibre of the optic-fibre layer, and 

 is continuous with the nucleated cone granule ; this is a bipolar 

 ganglion cell, the peripheric process of which is usually the 

 cone body itself. If, as often happens, especially at the macula 

 lutea, there is a long intervening space between the cone gra- 

 nule and cone corpuscle or body, this part, which constitutes the 

 peripheric portion of the cone fibre, is again thicker than the 

 other or central portion. The rod fibres are very much smaller 

 than the cone fibres. Whether they also are composed of 

 several fibrils cannot be determined from actual observation, 

 though it is on various grounds probable. The peripheric part of 

 the rod fibres, again, is far thicker than the centric ; each one 

 begins at the external granulated layer with a dilatation which 

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