Fig. 1. A section through the area of the forebrain of a 4-mm human embryo. Lateral outpocketings of the completely internalized neural ectoderm (NE) form the optic vesicles (OV). The surface ectoderm (SE) is still, at this stage, totally undifferentiated. Carnegie embryo 6097. (Smelser GK: Embryology and morphology of the lens. Invest Ophthalmol 4:398, 1965)