ANATOMY OF THE RETINA. 



683 



regarded as purely accessory disappear, leaving only the structures that are 

 concerned directly in the reception of visual impressions. 



The external granule-layer is composed of large granules, looking like 

 cells, which are each nearly filled with a single nucleus. These are connected 

 with the filaments from the rods and cones. They are rounded or ovoid 

 and measure from yy^nr to 60 * 00 of an inch (2 to 4 /*) in diameter. The 

 inter-granule layer (cone-fibre plexus) is composed apparently of minute 

 fibrillee and a few nuclei. The internal granule-layer is composed of cells 

 nearly like those of the external granule-layer, but a little larger, and prob- 



Fio. 247. Vertical section of the retina FIG. 248. Connection of the rods and cones 

 (H. Miiller). of the retina with the nervous elements 



(Sappey). 



FIG. 247. 1, 1, layer of rods and cones ; 2, rods ; 3, cones ; 4, 4, 5, 6, external granule-layer ; 7, inter- 

 granule layer (cone-fibre plexus) ; 8, internal granule-layer '; 9, 10, finely granular, gray layer ; 11, 

 layer of nerve-cells ; 12, 12, 12, 12, 14, 14, fibres of the optic nerve ; 13, membrana limitans. (The pig- 

 mentary layer is not shown in this figure.) 



FIG. 248. 1, 1, 2, 3, rods and cones, front view; 4, 5, 6, rods, side view; 7, 7, 8, 8, cells of the external and 

 internal granule-layers ; 9, cell, connected by a filament with subjacent cells ; 10, 13, nerve-cells con- 

 nected with cells of the granule-layers ; 11, 21, filaments connecting cells of the external and internal 

 granule-layers (12 is not in the figure); 14, 15, 16, 17, 18, 19, 20, 22, 23, 24, 25, 26, a rod and a cone, con- 

 nected with the cells of the granule-layers, with the nerve-cells and with the nerve-fibres. 



ably connected with the filaments of the rods and cones. The granular 

 layer is situated next the layer of ganglion-cells. 



The layer of ganglion-cells is composed of multipolar nerve-cells, measuring 

 TcW to -rfa of an inch (8 to 32 /A) in diameter. In the centre of the retina, 

 at the macula lutea, the cells present eight layers, and they diminish to a 

 single layer near the periphery. The smaller cells are situated near the cen- 



