THE VERTEBRATE EYE 



249 



external limiting membrane between the rods and cones and their 

 nuclei and an internal limiting membrane on the inner surface of the 

 nerve-fibre layer. Throughout the vertebrate phylum the structure of 

 the retina is remarkably constant, the layers varying only in the 



M> «=^ «ai • ^* Nomina vitrea 



^ "4i» (^ **niqmenf epithelium 



V I' 



Fig. 263.— The Humax Retina. 



At the left, the retina in the nasal fundus as it appears after fixation in 

 Kolmer's fluid, nitro-cellulose embedding, ]\Iallory's trij^le stain or Heiden- 

 hain's haematoxylin and phloxine. At the right, the neuronic hook-up of the 

 retina, with examples of its principal elements, as revealed by the Golgi 

 methods ( X .500) (Gordon Walls, based largely on the work of Polyak, 1941). 



o, amacrine cell (diffuse type) ; h, bipolar cells of ordinarj^ "midget" 

 type; c, cones; ch, "centrifugal" bipolar (believed to conduct outward 

 through the retina rather than inward) ; dh, diffuse bipolar cells, connecting 

 with many visual cells, chiefly rods ; g, ganglion cells of ordinary " midget " 

 type ; /;, horizontal cell with dendrites connecting only with cones, axon with 

 both rods and cones at some distance; m, Miiller's fibre (forms limiting mem- 

 branes) ; pg, " parasol" ganglion cell (one of .several giant types, connecting 

 with many bipolars) ; r, rods. 



regularity of their architecture and in the density and relative pre- 

 ponderance of their cellular elements ; even in Cyclostomes the typical 

 layering can be recognized although the various elements tend to be 

 intermingled, particularly the ganglion cells \\-ith the inner nuclear 

 layer. These minor variations which occur will be noted in the 

 subsequent chapters. 



