Fig. 1. Schematic drawing of the forebrain (F) and optic vesicles at about the 4-mm gestational stage. A cross-section of one vesicle shows neural ectoderm (NE) and surrounding surface ectoderm (SE). The vesicle (V) eventually develops into the globe, and the optic stalk (S) becomes the retrobulbar optic nerve. (Adapted from Mann I: Development of the Human Eye. New York, Grune & Stratton, 1969)