Medusa, Cagavaggio Merisi
On the Google Art Project. Click in the lower right of the image for zoom controls.
The original is in the Uffizi Gallery in Florence.
Students of drawing and anatomy may feel, as I do, that the mouth of the Medusa is painted as if from a head that is facing the viewer almost directly, while the head itself is turned three quarter and tilted at a different angle than would be a head associated with the position of the mouth.
Never one to shy way from drama or provocation (and a master of draftsmanship), Caravaggio has apparently deliberately twisted their relationship, subconsciously disconcerting the viewer and adding to the horror.
The work is painted on a shield, presumably representing the one on which Athena mounted the severed Gorgon’s head after receiving it from Perseus.