262 NORMAL HISTOLOGY. 



Miiller" (Fig. 243, x), which extend from this layer to the in- 

 ternal limiting membrane and serve to support the various elements 

 of the retina. The nuclei of these cells lie in the seventh layer, to 

 the granular character of which they contribute. The portion of 

 the cell which lies in the fourth layer of the retina is indented 

 with numerous oval depressions receiving the nuclei of the cells 

 carrying the rods and cones, which they both support and isolate 

 from each other. The filamentous cell-bodies of those elements 

 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." 



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, 

 which lies at various depths in different cells. The cell-body 

 expands again near the external limiting membrane, through which 

 it passes to form the rod. At the other end the filamentous cell- 

 body terminates in a minute knob in the fifth layer of the retina. 

 The cells which form the cones have nuclei lying near the external 

 limiting membrane and cylindrical bodies terminating in a brush 

 of filaments in the fifth layer. 



5. The outer molecular layer, also called the " outer plexiform 

 layer," owes its appearance to a multitude of filaments, part of which 

 have been described as the terminations of the cells bearing the rods 

 and cones, the rest being the terminations of nerve-processes spring- 

 ing from the cells of the sixth layer. 



6. The sixth layer has a granular appearance, because of the 

 presence within it of the cells of a great number of short neurons. 

 These are of two sorts : first, those belonging to the first type, rep- 

 resented in Fig. 217, which have dendrites in relation in the fifth 

 layer with the filaments of the cells bearing the rods and cones, and 

 neurites that come into relation in the seventh layer with the den- 

 drites of ganglion-cells lying in the eighth layer ; second, neurons 

 of the third type, shown in Fig. 217, which, in this situation 

 have been called " spongioblasts." These, which we may regard 

 as association-neurons, form two groups : first, those which send 



