77 8 SPECIAL SENSES. 



of connective-tissue elements. It is about -^^ of an inch in thickness. From this 

 membrane, connective-tissue elements are sent into the various layers of the retina, 

 where they form a framework for the support of the other structures. 



As we before remarked, the retina becomes progressively thinner from the centre to 

 the periphery. The granular layers and the nervous layers rapidly disappear in the 

 anterior half of the membrane. 



FIG. 245 (A). Vertical section of the retina. FIG. 245 (B). Connection of the rods and cones 



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



(Sappey.) 



FIG. 245 (A). 1, 1, layer of rods .and cones; 2, rods; 8, cones; 4, 4, 5, (5, 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 ; 18, membrana limitans. 



FIG. 245 (B). 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, 18, nerve-cells, connected 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, connnected with the cells of the granule-layers, with the 

 nerve-cells, and with the nerve-fibres. 



The connection between the rods and cones and the ganglion-cells may be readily 

 understood if we accept the following explanation: The filaments from the bases of the 

 rods and cones pass inward, presenting, in their course, the corpuscles which we have 

 described in the granule-layers, and finally become, as is thought, directly continuous 

 with the poles of the ganglion-cells. The cells, in their turn, send filaments to the layer 

 formed by the expansion of the optic nerve, which are continuous with the nerve-fibres. 

 This arrangement is shown in Tig. 245 (B). 



The arteries of the retina branch from the arteria centralis, presenting a beautifully 

 arborescent appearance when viewed with the ophthalmoscope. They pass into the layer 

 of gray nervous matter and send their branches to the periphery, where they supply a 

 wide plexus of very small capillaries in the ora serrata. The capillaries empty into an 



