THE EYE AND ITS APPENDAGES. 



353 



FIG. 377. 



The nerve-fibre-layer contains the continuations of the optic 

 fibres which, after having lost their medullary substance in their 

 passage through the lamina cribrosa, radiate as naked axis-cylin- 

 ders to all parts of the retina as far as the ora serrata. The fibre- 

 layer is thickest at the edge of the optic disk and thinnest at the 

 extreme retinal periphery. Sooner or later the fibres forsake their 

 peripherally-directed course, and, bending sharply, pass almost per- 

 pendicularly to the ganglion- 

 layer and other strata. 



The ganglion-cell-layer 

 consists of a single row of 

 large multipolar nerve- 

 cells (15 to 30 M), whose 

 axis-cylinder processes 

 are directed towards the fibre- 

 layer ; their branched pro- 

 toplasmic processes, when 

 well developed, pass into the 

 inner reticular zone, to meet 

 the arborizations of the cone- 

 bipolars. The ganglion- 

 cells in the central part of 

 the retina are densely packed 

 in the macula, constituting 

 overlying rows, but towards 

 the periphery they are less 

 plentiful, and at the ora ser- 

 rata infrequent. 



The inner reticular layer 

 presents a characteristic retic- 

 ulated tissue composed of 

 neuroglia net-works and 

 the rich arborizations of various nerve-cells ; the processes origi- 

 nate from both the elements of the ganglion-layer and the cells of 

 the adjacent nuclear stratum. 



The internal nuclear layer includes a number of distinct ele- 

 ments, and presents two subdivisions : (a) an inner layer of nerve- 

 cells, the spongioblasts, or amacrines, and () an outer layer 

 of the rod- and cone-bipolars forming the ganglion retinse. The 

 " spongioblasts" are not concerned in the production of the sus- 

 tentacular tissue, as their name given under erroneous ideas regard- 

 ing their function would imply, but are nervous elements whose 

 branched protoplasmic processes are resolved within the inner 

 reticular layer into arborizations. The cone-bipolars send their 



23 



Section of human retina : a, internal limiting mem- 

 brane formed by apposition of expanded basis of M til- 

 ler's fibres (y) ; b, fibre-layer; c, layer of ganglion-cells 

 (z) ; d, e, inner reticular and inner nuclear layer ; f, g, 

 outer reticular and outer nuclear layer ; h, outer limit- 

 ing membrane ; i, layer of rods and cones ; k, portion 

 of pigment-layer ; v, x, blood-vessels. 



