STRUCTURE OF THE RETINA 



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optic nerve is said to be upward of 1,000,000. The fibers of the optic nerve 

 spread out over the inner surface of the retina as far as the ora serrata. 



The retina itself consists of layers of nerve elements supported by deli- 

 cate connective tissue. The older descriptions recognize some eight or ten 

 layers in the retina. These appear in the ordinary microscopic preparations 

 and are shown in figure 446. But the newer investigations of Cajal, Golgi 

 Retzius, and others have shown that the retina is a much simpler structure 

 than heretofore described. The retina is formed of essentially three layers 

 of nerve cells. Naming from the center of the eye outward, they are: The 



H 



FIG. 447. Transverse Section of a Mammalian Retina. A, Layer of rods and cones; 

 B, bodies of visual cells (external granular); C, external molecular layer; E, layer of bipolar 

 cells (internal granular); F, internal molecular layer; G, layer of ganglionic cells; H, layer 

 of optic-nerve fibers; a, rod; b, cone; c, body of the cone cell; d, body of the rod cell; e, 

 bipolar rod cells;/, bipolar cone cells; g, h, i, j, k, ganglionic cells ramifying in the various 

 strata of the internal molecular zone; r, inferior arborization of the bipolar rod cells, con- 

 necting with the ganglionic cells; r, inferior arborization of the bipolar cone cells; /, epithelial 

 or Miiller cells; x, point of contact between the rods and their bipolar cells; z, point of con- 

 tact between the cones and their bipolar cells; s, centrifugal nerve fiber. (Cajal.) 



ganglionic layer; the layer of bipolar cells; and the layer of rods and cones, 

 figure 447. The cells of these layers have numerous fibrous processes which 

 interlock in such a way that they seem to form different areas when studied 

 in cross-section. If we recognize the strata of interlacing fibers, then the 

 following may be made out: 



The layer of ganglion cells . . 



The layer of bipolar cells . . . 

 The layer of visual cells 



1. Ganglionic layer, with the fibers of the 

 optic nerve. 



2. Internal molecular layer. 



3. Internal granular layer. 



4. The external molecular layer. 



5. The external granular layer. 



6. The layer of rods and cones. 



