1. The Sistine Madonna by Raphael
At first, you may get the impression that Pope Sixtus II has six fingers on his right hand. But a more careful inspection will have you realize that what you actually mistook for a sixth finger is actually part of his palm. In another part of the painting, the outgrowth next to the Madonna's little toe can be seen as a sign of polydactyly - an anomaly characterized by an extra number of digits.