VISUAL ORGAN. 351 



inner reticular layer. The nuclei of Muller's fibres also lie 

 at the level of the outer ganglionic layer. 



The inner reticular (molecular) layer (G) consists of a fine 

 network, which is derived mainly from the branched processes 

 of cells of the outer ganglionic layer, as well as the dendrites 

 of cells of the inner ganglionic layer. This layer shows stria- 

 tions parallel to the surface of the retina. This appearance is 

 due to the fact that the end arborizations of the cells lie at dif- 

 ferent levels (Fig. 263). Between the most external arboriza- 

 tions of the bipolar cells (e-i) belonging to the cones, and be- 

 tween the innermost branched dendrites of the ganglion cells 

 (o-s], there run the fine branches of the amakrine cells. Fine 

 side branches of the Muller's fibres (a) also take part in this 

 network. 



The inner ganglion-cell layer (Fig. 263, H] consists of 

 r,nulti polar ganglion cells with many protoplasmic processes, 

 which extend toward the outside, and at certain levels of the 

 inner reticular layer break up into fine branches. Retzius and 

 Cajal claim that each ganglion cell branches without forming 

 anastomoses with other cells. Dogiel believes, on the contrary, 

 that the protoplasmic processes of all ganglion cells of the 

 retina join with one another and form a network. The axis- 

 ylinder process extends inward and comes to lie in the nerve- 

 fibre layer as an independent nerve fibre. 



In the human retina a ganglion cell is sometimes found to 

 be bound to another by a short bridge. These are the so-called 

 twin cells (Dogiel, Greeff ). Such a bridge may vary in length, 

 and is only a thick protoplasmic process which is continuous 

 with that of another cell. Only one of two cells thus con- 

 nected possesses an axis-cylinder process, which passes over 

 into the nerve-fibre layer. 



In the inner ganglion-cell layer there lie cells (t) whose 

 dendrites pass diffusely through the whole thickness of the 

 inner reticular layer, but have no connection with the rods 

 and cones. 



The nerve-fibre layer (Fig. 263, J) contains the fibres of 

 the optic nerve, which diverge from one another in all direc- 



