344 



MANUAL OF HISTOLOGY. 



a, membrana limitans interna. 

 Z>, optic nerve fibre-layer. 



c, ganglion-cell layer. 



d, inner granular layer. 



e, inner nuclear layer. 



^ outer granular layer. 

 <7, outer nuclear layer. 

 7i, membrana limitans externa. 

 i, layer of rods and cones. 

 Pigment layer. 



The fibres of the optic nerve generally lose their medullary 

 sheath at the lamina cribrosa, and proceed 

 thence as naked axis- cylinders through the 

 opening in the choroid to the level of the 

 retina, where they spread over its entire in- 

 ner surface to form the nerve-fibre layer, 

 which is thick in the vicinity of the nerve, 

 but gradually decreases as it approaches 

 the ora serrata, where it ends. 



At the macula lutea the fibres do not 

 form a distinct layer, but, curving toward 

 this spot from above and below, are lost 

 in the layer of ganglion-cells, either entering 

 them or passing on to the inner granular 

 layer. 



The ganglion-cell layer consists of large 

 branching cells in most places but one row 

 deep, though near the macula there may 

 be two or more layers. They are very 

 transparent, have no visible cell-wall, and 

 are provided with a varying number of pro- 

 jecting arms ; when fresh they contain fine 

 granular matter with a clear, large nuclei 

 and nucleoli, and appear finely fibrillated. 



They receive an axis-cylinder on their 

 inner side, and on the outer send out 

 branches which ultimately divide into fine fibrillae, and are 

 lost at the inner granular layer in a tangled network. It is 

 probable, however, that some of these fibres are connected 

 with the cells of the inner nuclear layer. 



The inner granular layer partly surrounds the ganglion- 



FIG. 157. Transverpe sec- 

 tion of the retina. After Ze- 

 hender. 



