35 o NORMAL HISTOLOGY. 



The outer plexiform layer is a narrow granular looking stratum, 

 between the outer and the inner nuclear layer, and constitutes the first of the 

 cerebral layers of the retina. It is composed of the dendritic arborizations 

 of the bipolar nerve-cells of the succeeding layer, which lie in close relation 

 with the foot-plates of the cone-cells and with the end-knobs of the rod-fibres. 



The inner nuclear layer, the most complicated of the retinal strata, 

 measures 35 /* in thickness, near the optic disk. It contains nervous elements 

 of three main types the horizontal cells, the bipolar cells, and the amacrine 

 cells. 



The horizontal cells have flattened cell-bodies and send out dendrites, 

 which terminate in close association with the bases of the rod- and cone-visual 

 cells. Each horizontal cell possesses also an axone, which ends in a richly 

 branched arborization about the visual cells. The function of the horizontal 

 cells is not well understood, but they probably serve as association fibres 

 between the visual cells. 



The bipolar cells, the ganglion- cells of this layer, are of two chief 

 varieties, the rod-bipolars and the cone-bipolars. They are oval cells, each 

 sending an axone inwards, which ends in relation with the large nerve-cells of 

 the ganglion-cell layer, and a dendrite outwards, which is associated with the 

 visual cells. 



The amacrine cells are placed in the inner portion of the nuclear layer. 

 They are nerve-cells, although no distinct axone can be demonstrated. 

 They possess, however, richly branched dendritic processes, which ramify 

 in the inner plexiform layer. 



The inner plexiform layer, 40 n thick, appears granular, similar to 

 the corresponding outer zone, and is composed of the interlacing axones of 

 the bipolar, amacrine and horizontal cells from the inner nuclear layer and 

 the dendrites of the large ganglion-cells in the subjacent retinal layer. Inter- 

 mingled with these are the fibres of Miiller, which show as conspicuous 

 vertical striae, with lateral offshoots. 



The layer of ganglion-cells consists, throughout the greater part of 

 the retina, of a single row of large multipolar neurones, each with a cell- 

 body containing a vesicular nucleus and nucleolus and exhibiting typical 

 Nissl bodies and a fibrillar structure. Their axones pass inwards and become 

 the nerve-fibres of the fibre layer. Converging towards the optic entrance, 

 they become consolidated into the optic nerve and continue to the brain. The 

 dendrites of the ganglion-cells, one to three in number, run outwards into the 

 inner plexiform layer and end as richly branched arborizations in connection 

 with the centrally directed processes from the bipolar cells. 



The nerve-fibre layer is composed almost entirely, but not exclusively, 

 of the axones of the ganglion-cells of the preceding layer. The individual 

 fibres are collected into bundles of varying size, which take a horizontal 

 course and converge towards the optic disk. Within the retina they are 

 devoid of medullary sheaths, but acquire them after passing through the 

 lamina cribrosa of the sclera. A few of the fibres are centrifiigal, arising 

 from ganglion-cells within the brain, and terminate apparently in relation 

 with the amacrines of the inner nuclear layer. 



The sustentacular tissue, the neuroglia of the retina, exists in two 

 forms as \\\Q fibres of Miiller and the spider cells. 



The fibres of Miiller are modified neuroglia-fibres, which pass ver- 

 tically from the inner surface of the retina through the succeeding layers as 

 far as the bases of the rods and cones (Fig. 400). The inner extremities of 

 the fibres are conical expansions, that by apposition form an incomplete 



