The periphery of the avian retina: specializations of the layer of ganglion cells and their axons.

Ganglion cells and their axons were studied in the retinas of chicken, quails and pigeons. Retinal flat mounts were examined with light microscopy after cresyl violet or silver impregnation procedures. Silver-impregnated specimens were also examined with scanning electron microscopy. Significant differences were observed between ganglion cells of the central region and those lying along the temporal and nasal margins of the retina. These peripheral ganglion cells formed belt-like structures where groups of cell bodies were arranged in stripes. Their axons did not make a straight course and they reached the nerve head after an arciform path. Axon bundles and stripes of cells were similarly oriented. Consequently, axons originating in the same region of the retina did not necessarily arrive to the same point of the nerve head. Both the nasal and the temporal belts contained the largest neuronal bodies found in the retina. However, there were more cellular stripes in the temporal belt than along the nasal margin. In some birds, the belts developed after hatching.