The permanent smile was not studied in Europe till the Milanese school was founded, and in this nearly every artist gave his attention to it, following the example of Lionardo. This great master, who was well acquainted with the principles of art, is not likely to have had in his mind an evanescent expression when he experimented with the smile, and one can hardly understand therefore why this feature is almost invariably over-emphasized in his works. In his portrayal of women he used both eyes and mouth to bring about the smile,[a] and more commonly than not paid most attention to the eyes. Perhaps he had in view the production of a permanent smile solely by means of the eyes, which play so great a part in general expression. In nature it is physically impossible for a smile to be produced without a faint variation in the mouth line, while the lower eyelids may remain perfectly free from any change in light and shade, even with a smile more pronounced than is necessary for apparent permanence. In the Mona Lisa at Boston,[56] the smile is very faintly indicated by the eyes, and most pronounced at the mouth, while in the famous Paris picture, the eyes are chiefly responsible for the smile, the mouth only slightly assisting.[57] Many smiling faces were produced by others of the Milanese school, and as a rule the mouth only was used, often with complete success, notably by B. Luini,[b] Pedrini,[c] and Ferrari.[d] Raphael never used the eyes to assist in producing a smile, except with the Child Christ,[e] and in all cases where he exhibits a smile in a Madonna[f] or portrait,[g] it appears definitely permanent. As a rule the great artists of the Renaissance other than the disciples of Lionardo, rarely produced a smile with the intention of suggesting a permanently happy expression, and in the seventeenth century little attention was given to it. [a] An exception where the mouth only is used is a drawing for the Madonna and Child with St. Anne, Burlington House, London. [b] Salome, Uffizi Gallery, Florence. [c] Madonna and Child, Arezzo. [d] Madonna and Child, Brera, Milan. [e] Cowper Madonna, Panshanger, England. [f] See Casa Tempi Madonna, Munich; and Virgin with a Goldfinch, Uffizi. [g] Portrait of a Young Man, Budapest; and the Fornarina, Barberini Gallery, Florence.