Abstract
The similarity of the developmental anatomy of chicken with that of mammals has rendered it an appropriate animal model for understanding the anatomical and pathological aspects of human biological systems. The present study describes the age-dependent morphological differentiation stages of developing retina of chick embryos. The retinae of chicken embryos of ages 10 and 15 days incubation, of newly hatched chicks and also that of adult chicken were studied histologically. The retinae were processed both for routine microscopy and as araldite-embedded high-resolution sections. At all ages, different retinal layers were studied noting the changing shapes of nuclei and measuring the individual layer thickness. As the animal advances in age, the elongated to oval nuclear shape takes on a more round contour, the pigment content gradually increases, the initial cuboidal cells of the photoreceptor layer change over to tall columnar cells, their outer segments pushing their way into the epithelium layer, producing vacuolar appearances among the pigment granules, the inner and outer plexiform layers increase in thickness, while the nuclear layers, becoming more compact, decrease in thickness. The ganglion cell layer, initially multilayered, gradually becomes single-cell-layered with advancing age. This descriptive laboratory research presents a detailed retinal differentiation pattern, which contributes to the anatomical knowledge of retinal embryology as well as providing a comparative background for pathological deviations.