THE PIGMENT EPITHELIUM 



43 



of the latter in bright and dim Hght. Pigment may be entirely lacking 

 over a large area of the epithelium where this lies against an especially 

 modified area of chorioid (Chapter 9, section D). 



* lamina vllrea 

 ** pigment epithelium 



receptor layei 



'" >c»>v^ "^^m." ^-extllmrmem^.^ 

 ^ '^^J^ outernuclear 



•^^'i^- ^'\'^" 



X'-^-lJ' \ outer plexi- 

 !*?V rr *^ ^1 form layer 



'i^^c\^^'^li T 



^r«4^ ^^^■^m.'nner nuclear 



inner plexi- 

 form layer 





L^ 



) ganglion layer ^ 



nerve fibers 



■^'iRtrllmrmemb: 



Fig. 19 — The human retina. 



At the left, a vertical seaion through the retina in the nasal fundus, as it appears in ordin- 

 ary histological preparations (fixation in Kolmer's fluid; nitrocellulose embedding; Mallory's 

 triple stain, Heidenhain's hematoxylin and phloxine). x 500. (Note cross-section of capillary 

 in inner nuclear layer). 



At the right, a 'wiring diagram' of the retina showing examples of its principal elements, 

 as revealed in material impregnated with silver by the methods of Golgi. Based largely upon 

 the work of Polyak. 



a- amacrine cell (diffuse type); b,b- bipolar cells (ordinary, 'midget' type); c,c- cones; 

 cb- 'centrifugal' bipolar, believed by Polyak to conduct outward through the retina rather 

 than inward; db- diffuse bipolar, connecting with many visual cells — chiefly rods; g, g- 

 ganglion cells (ordinary, 'midget' type); h- horizontal cell — its dendrites connecting only 

 with cones and its axon with both rods and cones at some distance from the cell-body; 

 m- Miiller fiber — its ends forming the limiting membranes and its substance serving to 

 insulate the nervous elements from each other except at synapses; pg- 'parasol' ganglion 

 cell (one of several giant types, conneaing with many bipolars) ; r, r- rods. 



