The prenatal development of the mouse eye

The development of the eye has been studied in mouse embryos from the ninth day through the nineteenth day of gestation. The tissue was fixed in aldehydes, post‐osmicated and embedded in Epon. The entire eye was sectioned and studied under the light microscope. The development of the eye in the prenatal period is described as having seven stages. In the first stage, the close contact of the optic vesicle with the surface ectoderm is observed. The retinal disc and lens placode begins to form. The second stage shows the invagination of the optic vesicle and the contraction of the margin of the lens pit. In the third stage, the optic cup differentiates into an outer pigment epithelium and an inner retinal layer. The cells of the posterior lens wall start to elongate. During the fourth stage, the cavity of the lens vesicle is completely obliterated by primary lens fibers and the inner neuroblastic layer of the retina is formed with nerve fibers being traced from its cells to the optic stalk. The fifth stage is dominated by the appearance of lids, cornea and optic nerve, the formation of the anterior chamber and the consolidation of the intraocular portion of the embryonic vascular system. In the sixth stage, the eyelids fuse and the anterior margin of the optic cup begins to grow actively. In the last prenatal stage, the third neuron layer of the retina begins to differentiate. The iris and the folds of the ciliary body can be detected.