The figure was that of a man [St. Bartholomew] without a skin; with every vein, artery, muscle, every fibre and tendon and tissue of the human frame, represented in detail. It looked natural, because somehow it looked as if it were in pain. A skinned man would be likely to look that way, unless his attention were occupied with some other matter. It was a hideous thing, and yet there was a fascination about it some where. I am sorry I saw it, because I shall always see it, now. I shall dream of it, sometimes. I shall dream that it is resting its corded arms on the bed's head and looking down on me with its dead eyes; I shall dream that it is stretched between the sheets with me and touching me with its exposed muscles and its stringy cold legs."
Here he is -- Bart that is, not Twain -- if you're curious. And some other views.