276 



NORMA L HISTOLOG Y. 



are also separated by the cells of Miiller. In the sixth and seventh 

 layers delicate processes from these cells serve a similar purpose, 

 and in the eighth layer their deep extremities fork to give support 

 to the ganglion-cells. Beyond the ninth layer the ends of these 

 forks expand and come in contact with each other at their edges 

 to form the " internal limiting membrane." 



Fig. 253. 



VIII. 



Diagram of the retina. (Kallius.) I., pigmented epithelial layer; II., layer of the rods and 

 cones; III., external limiting membrane; IV., outer granular layer ; V., outer molecular 

 layer; VI., inner granular layer; VII., inner molecular layer; VIII., ganglionic layer; 

 IX., layer of nerve-fibres, z, pigmented epithelial cells; a, at the bottom of the external 

 limiting membrane, rods ; 6, cone cells ; c-h, ganglion-cells of the sixth layer connecting 

 the fourth layer with the eighth; i, horizontal cell sending a process into the seventh 

 layer; k-q, "spongioblasts," or neurons of the third type (Fig. 232); r-w, ganglion-cells 

 of the eighth layer; x, sustentacular cell of Miiller, with striated upper end forming 

 a part of the external limiting membrane; y, y, neuroglia-cells. It should be borne in 

 mind that in sections of the retina numerous elements of the various sorts here rep- 

 resented are crowded together to form a compact tissue. The centrifugal fibres which 

 reach the retina from the cerebrum are omitted from this diagram. They are distributed 

 in the inner granular or sixth layer. The light entering the eye passes through the layers 

 represented in the lower part of this figure before it can affect the rods and cones. 



4. The fourth, or outer granular layer contains, as already stated, 

 the nuclei and elongated bodies of the cells that carry the rods and 

 cones of the second layer. The bodies of the former are almost 

 filamentous in character, but expand to enclose the oval nucleus, 



