ok . . . I looked at the song seriously lately (about to start singing it . . .)and noted the breastbone reference . . .looked up the following http://www.labartlibrary.com/symbiosis/humanatright6.html
and noted that the sternum (real name of "breastbone") was a short usless thing incapable of being converted to anything more than a stick for a dog . . . (No, silly, you throw it so the dog can fetch, not hit the dog! . . . )
Note that on the same wonderful page there is a piccy of ribs . . . .large and curved . . they would fit the bill perfectly, if a tad tiny.
I am not sure about the soundboard but this is a fantasy song rememeber?
Always keep in mind that it played by iteslf . . .anything is possible, folks! (wish my guitar could do that trick . . that way I could accompany myself on the mandolin or dulcimer!! . . .)