Fig. 4. Scheme to show the development of the lens. A. Lens thickening. B. Lens pit. C. Lens pit closing. D. Lens vesicle. E. Elongation of cells of the posterior wall of the lens vesicle. F. Obliteration of the cavity of the lens vesicle by cells of the posterior wall. G. Formation of lens sutures by the meeting of fibers developed in the equatorial region. (Mann I: The Development of the Human Eye. New York, Grune Stratton, 1950)