I have begun an album, Cézanne at the Louvre, because he made so many drawings there. I still don't have quite what I was looking for, but I can add to it when possible, and, even though the views are not ideal the point can still be made.
An earlier post distinguished art to illustrate or celebrate from art for its own sake.
The relationship of existing art and living artists is different. Here I do not mean artists using existing works to make a statement about art, especially in post-modern art, but artists using existing pictures and sculptures just as they use nature. I mean, Monet used the façade of Rouen Cathedral and Haystacks and avenues of Poplars all alike. And Cézane, though he was bashful enough to prefer a Death of Sardanapalus or any other pre-existing symplegma to a studio full of naked models and, especially in his youth, copied a number of such works for not only formal interest but also their subject matter, he also, drawing or drawing with watercolor added, studied statues both ancient and modern (not only Michelangelo but also, e.g., Puget) in exactly the same way, exploring the essential forms, as he did skulls and apples and the limestone (I think) formations on his own land.
And when an artist like Cézanne takes an elaborately twisted Eros teasing an agonized old Centaur, he draws it so that you know that he sees what its originator meant, not about the teasing subject, a conversation piece, but about the sculpture. We don't know the Hellenistic sculptor's name, but his Eros is easily the equal of Verrocchio's putto in Florence at the Palazzo Vecchio. I am almost certain that I have seen other Cézanne drawings of the Borghese Centaur, but I'll have to add them when I find them.
(the apples and the bather are, of course, extraneous)
(the Hadrianic, Tivoli, black basalt centaur in Rome is more academic and has no Eros)
In this case Cézanne studies the forms just as if this were one of the Michelangelo Slaves, and never mind the playful erotic subject matter.
But when Cézanne sees something in a sculpture, such as foreshortened forms that are always essentially important to his art, he doesn't mind that it is the Sleeping Hermaphrodite (with its tufted mattress, which may have come from Bernini's studio but does not belong to it). Indeed, if the 'scandalous' front view were as sculpturally interesting he might even have drawn that, though (I daresay, from studying his drawings as a whole) not with any emphasis on the combination of breasts and penis.
Note that Cézanne was not interested in the facial features, either. I apologize for my 1982 photograph. Somewhere I must have a better one.
Postscript: the book with a whole chapter on Cézanne at the Louvre is the large illustrated edition of John Rewald's classic monograph on Cézanne. The illustrations are, of course, under copyright...