Daniel B. Gallagher reviews the exhibition Figure, Memorie, Spazio: disegni da Fra’Angelico a Leonardo which was on view at Galleria degli Uffizi and Gabinetto Disegni e Stampe degli Uffizi, Florence (closed June 12, 2011).  Gallagher writes: "Precisely because drawing was considered an indispensable daily discipline, it became the privileged means of unlocking the cognitive processes that led masters to produce their greatest work. Whereas we tend to approach sketchbooks as modern-day detectives, at the time they were produced, budding apprentices knew full well that they were the most reliable entryway into the minds of their teachers."