If you write historicals set in a period where women corsetted down to waist measurements less than twenty inches, here are some reference photos. The link goes to Snopes, to an article debunking the claim that the pictured woman has had ribs surgically removed. The photos are real, but she's never had surgery; it's all from corsetting. The lady in question has a 15" waist, described as being "about the same size as a regular jar of mayonnaise."
The look is kind of grotesque, actually, but I do recognize that silhouette from late-period Victorian photos. I remember one or two photos of women with waistlines just like this, and (apparently also just like these photos) the descriptions claimed that the women had had the floating ribs surgically removed. We see here that that's not necessary to achieve this look.
The woman in the pictures, Cathie Jung, said that the floating ribs are flexible and they just moved over time. It makes sense, actually.
Another thing that's interesting is that Ms. Jung is 71, and didn't start corsetting until she was in her forties. That's another Victorian myth blasted -- the idea that you can't have a really tiny waist unless you start corsetting as a child or young teen. I think it was more likely the fact that women started looking for husbands at a very young age back then, and wanted to have the perfect look by their mid-teens. Display packaging and all that.