you do know that the dragon's hide vanishes when you steal its soul, right?
Certainly, I'm saying that even when the body is reduced to just a skeleton held together by cartilage, ligaments and tendons and such, even then some bones would be covered by others. The skull in itself is made of more bones than can be seen from the outside. To count them all you'd have to be able to actually dismantle the skeleton. Some bones are very small; think about the bones in the inner ear, after all.
Here's a cattle skull: http://image.shutterstock.com/display_pic_with_logo/88460/88460,1178210206,6/stock-photo-cattle-skull-3218800.jpg Think about how you'd have to be able to take such a skull apart to count all the bones composing it.
Somebody was mentioning horns; some animals have bony cores to their horns, like cattle, but others, like rhinos, do not. Rhino horns are made of hair, I believe, despite being thoroughly deadly. Ceratopsian horns were definitely keratin over a bony core, though.