This is the most magnificent drawing by Michelangelo in the United States. A male studio assistant posed for the anatomical study, which was preparatory for the Libyan Sibyl, one of the female seers frescoed on the ceiling of the Sistine Chapel (Vatican Palace) in 1508-12. In the fresco, the figure is clothed except for her powerful shoulders and arms, and has an elaborately braided coiffure. Michelangelo used the present sheet to explore the elements that were crucial in the elegant resolution of the figure’s pose, especially the counterpoint twist of shoulders and hips and the manner of weight-bearing on her toe. Recent research shows that this sheet of studies was owned by the Buonarroti family soon after Michelangelo’s death. The “no. 21” inscribed on the verso of the sheet (at lower center) fits precisely into a numerical sequence found on many other drawings by the artist that have this early Buonarroti family provenance.