ANATOMY OF THE FUNDUS ORGANS IN BIRDS 



17 



more so than in Mammals. There are no 

 separate bipolar or optical ganglion cells in 

 Birds, while we find in Mammals isolated 

 amacrine cells, and, in reptiles, bipolar cells. 

 All birds possess rods as well as cones, 

 although in very different arrangements. 

 H. Miiller erroneously depicted the cones of 

 the Pigeon with long cylindrical extremities, 



Figs. 8, 9 and 10 



The Retina of Various Vertebrates 



Fig. 8, Lizard; Fig. 9, Bird (Common Crow) ; Fig. 10, Mammal 



(Dog). X510. (After P. Chiarini.) 



when these really belong to the rods. The 

 cones have each a single oil droplet, whose 

 color varies. Cajal has differentiated (in 

 Birds and in Reptiles) "straight" and 

 "oblique" cones. 



The nuclei of the cones usually lie inside 

 the membrana limitans externa of the retina. 

 Several "oblique" cones have an enlarge- 

 ment of the end inside the inner layer of 

 nuclei. The "twin" cones, whose nuclei are 

 not to be seen, lie near the membrana limitans; 

 the smaller nucleus of the pair is in a facet of 

 the larger. The rod nuclei are usually found 

 in the internal half of the nuclear layer. Their 

 small end branches in the outer reticular 



layer, stretching out farther than the end of 

 the cone. The rod in nocturnal birds ends 

 in the external portion of the outer reticular 

 layer with a nodosity — a little ball at the 

 end without any branches. 



Cajal differentiates three superimposed 

 plexuses in the external retinal layer; the first, 

 composed of the basal fibrils of the rods; 

 the second, the end-threads of the 

 straight cones; the third, fibrils 

 which emanate from the oblique 

 cones, that in every cell come in 

 contact with the dendrites of cer- 

 tain bipolars and longitudinal gan- 

 glion cells. 



Just as in Reptiles, Schieffer- 

 decker found in the Chicken, Crow 

 and Goose, in the external reticular 

 nuclear layer, concentric supporting 

 cells without nuclei. 



The inner nuclear layer of the re- 

 tina. One finds on the extreme 

 outer aspect horizontal ganglion 

 cells and (a) brush-like cells of Cajal, 

 with many projections and a long 

 horizontal cylinder which, like the 

 short projections, bends around the 

 outer reticularis and ends there 

 with an enlargement and branches; 

 (6) star-like cells with somewhat 

 longer dendrites and a short cylin- 

 der which first turns in and then 

 out. Between, and further in than 

 the cells, which Schiefferdecker calls 

 nucleated cells, are found two kinds 

 of bipolars; first, outer bipolars with highly 

 developed dendrites, and internal, small or 

 thin bipolars with weaker dendrites. The 

 thick bipolars seem to branch out in the fifth 

 layer of the internal reticularis; the thin 

 bipolars assume more the form of a layer in 

 the inner reticularis. 



As in all animals, the nuclei of the sup- 

 porting fibres of Miiller in the avian retina 

 are situated in the internal nuclear layer. 



In the inner portion of the internal nuclear 

 layer are found, as ganglion cells, the layer 

 of amacrine cells, which are divided, both in 

 Birds and Reptilia, into (1) nervous and 

 (2) proper amacrine cells. 



