I'd actually suggest the dragon has physiology more like that of a dinosaur. Hollow bones that allow for flight. Since (supposedly) dinosaurs shared lots of traits in common with birds, I'd say they'd be more like the owl example, regurgitating undigested bits.
Or even more possible would be a very wicked digestion. Some of the enzymes in the stomach/other tracts that allow the expulsion of purple lightning should be able to dissolve bone without too much trouble.
Though I do like the image of dragons being more like cats, especially if they're intelligent and prone to playing with their prey
