All these drawings are indubitably by the hand of Michelangelo, and must be reckoned among his first free efforts to construct a working plan. The Albertina Collection at Vienna yields us an elaborate design for the sacristy, which appears to have been worked up from some of the rougher sketches. It is executed in pen, shaded with bistre, and belongs to what I have ventured to describe as office work. It may have been prepared for the inspection of Leo and the Cardinal. Here we have the sarcophagi in pairs, recumbent figures stretched upon a shallow curve inverted, colossal orders of a bastard Ionic type, a great central niche framing a seated Madonna, two male figures in side niches, suggestive of Giuliano and Lorenzo as they were at last conceived, four allegorical statues, and, to crown the whole structure, candelabra of a peculiar shape, with a central round, supported by two naked genii. It is difficult, as I have before observed, to be sure how much of the drawings executed in this way can be ascribed with safety to Michelangelo himself. They are carefully outlined, with the precision of a working architect; but the sculptural details bear the aspect of what may be termed a generic Florentine style of draughtsmanship.
Two important letters from Michelangelo to Fattucci, written in October 1525 and April 1526, show that he had then abandoned the original scheme, and adopted one which was all but carried into effect. "I am working as hard as I can, and in fifteen days I shall begin the other captain. Afterwards the only important things left will be the four rivers. The four statues on the sarcophagi, the four figures on the ground which are the rivers, the two captains, and Our Lady, who is to be placed upon the tomb at the head of the chapel; these are what I mean to do with my own hand. Of these I have begun six; and I have good hope of finishing them in due time, and carrying the others forward in part, which do not signify so much." The six he had begun are clearly the Dukes and their attendant figures of Day, Night, Dawn, Evening. The Madonna, one of his noblest works, came within a short distance of completion. SS. Cosimo and Damiano passed into the hands of Montelupo and Montorsoli. Of the four rivers we have only fragments in the shape of some exquisite little models. Where they could have been conveniently placed is difficult to imagine; possibly they were abandoned from a feeling that the chapel would be overcrowded.