Applying his methodical approach to proportions, Lequeu used a protractor to draw a mouth frontally and in profile. As diagrammed, the contour of lips drawn according to this method would be derived from a series of curved arches extrapolated from a sequence of fixed points. The commentary compares the sinuous line of a closed mouth to a cupid’s bow, evoking the “sweet melancholy smile” of Venus’s “perfect mouth.”