The Development of the Cornea in the Chick

The development of the cornea in the chick, based on the microscopical examination of serial sections of 108 morphologically staged chick embryos between stage 26 and hatching, is described. A description of the adult cornea is also provided. Correlations between the internal histogenesis of the cornea and the external morphology of the chick embryo have been established from the use of staged embryos, so that the probable state of development of the cornea can be assessed from surface appearances only. The cornea of the chick, at stage 26, consists of an anterior epithelium, an acellular postepithelial layer, and a mesothelium. Mesenchymal cells (corneal ‘corpuscles’) begin to infiltrate the postepithelial layer at stage 27. By stages 29–31 these cells occupy a continuous layer, the substantia propria, which comprises the entire extent of the postepithelial layer except for an anterior, acellular band subjacent to the anterior epithelium. The anterior band becomes progressively thinner and disappears at stage 36, the substantia propria then extending across the entire distance between the anterior epithelium and the mesothelium. The anterior limiting lamina first appears at stage 39. It closely resembles and is often confused with the temporary anterior band of the postepithelial layer. The posterior limiting lamina was not identified with certainty in any of the embryonic corneae examined. It has been stressed that embryological studies in which external staging and internal development are correlated provide a more precise interpretation of developmental processes, and are an essential prelude to experimental, physiological, biochemical, and histochemical investigations of embryonic development.