Fig. 14. Schematic diagram of the developing cornea—central region. A. At 39 days, the two-layered epithelium rests on a basal lamina. It is separated from a two-to three-layered “endothelium” by a narrow, cellular space. B. At 7 weeks, mesenchyme from the periphery migrates into the space between epithelium and endothelium. It is the precursor of the future corneal stroma. C. The mesenchyme (fibroblasts) is arranged in four to five incomplete layers by 7½ weeks and a few collagen fibrils appear among them. D. By 3 months, the epithelium has 2 to 3 layers of cells and the stroma about 25 to 30 layers of fibroblasts (keratoblasts) that are more regularly arranged in its posterior half. There is a thin, uneven Descemet's membrane between the most posterior keratoblasts and the monolayered endothelium. E. By midterm (4.5 months) some “wing cells” are forming above the basal epithelial cells and an indefinite, acellular Bowman's membrane emerges beneath the basal lamina. About one third of the anterior portion of the multilayered stroma has its keratoblasts ina disorganized formation. Descemet's membrane is well developed. F. At 7 months the cornea has its adult structure established. A few mostly superficial keratoblasts are still randomly oriented with respect to the corneal surface. The collagenous lamellae in the rest of the stroma are in parallel array with only a few spaces in the matrix lacking collagen fibrils. Breaks (near the bottom of E and F) indicate that the central portion of the stroma is not represented.