When did vagina become a synonym for crotch?

One of my old high school buddies, a fellow who is now a renowned professor of art history, shared a link on Facebook to an article  that intrigued me, although probably not quite in the way most people would react. The big issue for most people would be the legal standing of the French court system to sue Facebook, an American company. No doubt it's an interesting legal question, as is the one regarding where you draw the line between art and porn, but that's not what caught my eye. Nope, what caught my eye was the way article after article (I did some Googling) referred to the image in question as a "painting of a vagina."

First, some background. According to the news articles I found, a man in France filed a lawsuit against Facebook when Facebook removed his photograph of a 19th century painting by the artist Gustave Courbet. The painting in question, "Origin of the World" is a realistic portrayal of an adult woman's crotch, the pubic region, her genital area. It is what in the parlance of porn would once have been called a beaver shot. Facebook considered it to be a pornographic image and therefore in violation of their policies.

By today's standards, the painting is remarkably innocuous. Thanks to the wide spread popularity of waxing, if a person just glances at the painting, what registers is not an explicit crotch shot but instead an image not a whole lot different than what you'd see if a woman was wearing a thong, except instead of fabric in the painting the external genitalia are rather obscured by pubic hair.* Courbet was, after all, a 19th century artist. The phrase "full Brazilian" did not yet exist, and for sure even the pornographers of his day never contemplated someday not just showing hairless vulvas, but doing such extreme close-ups of female genitalia that the line between an anatomy text and smut gets blurred. In short, nowhere in that painting do you actually see even a hint of a vagina.

If you look closer, of course, you can see that Courbet was a thorough Realist.** He did a really nice job of painting the individual hairs, and the labia majora are visible. Still, not a vagina.  The vagina is an internal organ, a passageway, it's not a crotch covered with fur. So why did all the news articles persist in referring to it as a painting of a vagina?

I don't know, but I have been noticing this shift in language. There are a number of words and phrases that would accurately describe what the painting shows, some polite (genital area, pubic region), some a little cruder (crotch), and some vulgar (twat, cunt). Vulva would be more anatomically correct -- vulva refers to the area around the vaginal opening. So why call a crotch a vagina? By definition, and I quote, a vagina is "The passage leading from the opening of the vulva to the cervix of the uterus in female mammals." It's internal, not external. Can I blame Eve Ensler? I've never seen "The Vagina Monologues" so I'm not sure. Is it just sloppy thinking? Lazy writing? Why use two words that have a more precise meaning when you can use one that's sort of related? It's a mystery. 

*It did occur to me that for many young American males the most shocking thing about that painting could be the discovery that women are not naturally as hairless as Barbie dolls. 

**After looking at a number of other paintings by Courbet, I concluded he was a lot better with nudes than he was with the outdoor and hunting scenes that seem to constitute the bulk of his work. Technically, he's quite good; aesthetically, however, he seemed to crank out some rather cliched images. And he definitely didn't handle light as competently as some of his contemporaries did.