Fig. 2. A section through the newly forming lens placode (LP) of a 4.5-mm human embryo. The surface ectoderm has been induced to elongate by the neural ectoderm (shown here already beginning to differentiate into the presumptive retina). The lens pit (fovea lentis) is barely discernible as a slight indentation below center in the surface of the placode (arrow). Carnegie embryo 8119. (Smelser GK: Embryology and morphology of the lens. Invest Ophthalmol 4:398, 1965)