Fig. 2. The optic cup, formed by an invagination of the outer wall of an optic vesicle. The vertical opening present in the inferior half of the optic cup is the embryonic fissure (EF). The optic stalk (S) is shown, and the fissure can be seen extending posteriorly along its inferior aspect. (Adapted from Mann I: Development of the Human Eye. New York, Grune & Stratton, 1969)