The transparent tissue constituting the anterior sixth of the outer wall of the eye, with a 7.7 mm radius of curvature as contrasted with 13.5mm of the sclera; it consists of stratified squamous epithelium continuous with that of the conjunctiva, a substantia propria, substantially regularly arranged collagen imbedded in mucopolysaccharide, and an inner layer of endothelium. It is the chief refractory structure of the eye.