Having grown up in the hills of Arkansas I knew a great folk musician named Jimmy Driftwood who played a guitar his father make out of the wood from the wagon seat their family had originally come to Arkansas in. He also played a Mouth Bow which he taught me how to make and play. It's probably on of the oldest types of string insturments in the world. We made ours from a barrel stave sanded down thin and attached a wire through a hole at one end and through the other end onto a tuning peg(friction). One plays it by holding it up to your cheek with your mouth open. You then vary the volume inside your mouth for the "notes". On a good day I can get about 6 or 7.
Buffy St.Marie used to play the Native American version of the Mouth Bow on several of her records.