It belonged to the uncle of someone named Tom. (no relation to Tom Bombadil, as far as we know)
Trivia note: the melody is the same as the traditional ballad, "The Fox" (no relation to the fox who observed the hobbit's departure, as far as we know).
The curious can see the original words to the ballad
here. There's also a link to a performance of the song by Peter, Paul and Mary (no relation to The_Mary, as far as we know).
I forget which bone it is - I could look it up, but that would be cheating, wouldn't it?