By Marine Pennetier PARIS, Feb 7 (Reuters) - A French art collector claims to have found the head from the nude body that appears in a famously explicit 19th Century oil painting of a woman's genitalia. Art expert Jean-Jacques Fernier, who has studied the works of Gustave Courbet for years, told Reuters he believed an unsigned painting of a woman's head, featured in this week's Paris Match magazine, had been cut off his masterpiece "The Origin of the World".