Topographical development of the ganglion cell fiber layer in the chick retina. A whole mount study

Abstract

Abstract Three hundred and forty whole mounts of retinas from domestic fowl aged two days of incubation to several months post‐hatching were examined using a modified pyridine‐silver technique. The first visible ganglion cell axons appeared near the posterior retinal pole between two and three days of incubation. These early axons grew immediately toward the optic stalk and became grouped in fascicles even before reaching it. The fascicles increased in number, diameter and length, became interconnected and became more parallel and orderly with age. The mean fascicle diameter and concentration increased with nearness to the optic fissure. Growth cones were seen only in the most vitread portion of the fiber layer. Two main groups of fascicles, one superficial and one deep, surrounded the head of the fissure by five days of incubation, each group entering the fissure at a different angle. At this time an arcuate pattern of fibers arose near the posterior pole of the retina. Fiber bundles were relatively thin and sparse in the center of this pattern. The distance between the fissure and the center of the pattern increased with age. The arcuate pattern virtually disappeared within several weeks, possibly indicating an abortive formation of a macula and fovea. The fibers at the periphery of the older retinas ran parallel to the iris, encircling but not entering it. These circumferential fibers, which first developed on the temporal side of the retina and later nasally, diverged from a point on the dorsal periphery of the retina. The relative position of this divergence point swung about 90° around the retinal periphery between five and one‐half and eight days of incubation. Probable centrifugal fibers were first seen at 17 days of incubation.