Much better, although now the thumb looks a bit like a bent hose. Remember that bones are rigid, and only the joints can bend; everything in between the joints is more or less static (well, obviously subjected to a bit of stretching sometimes, but y'know). You can approximate this with cylinders connected by spheres, although obviously the thumb is a bit meatier than a straight cylinder.

If need be, i can provide an example later. Until then though, try clenching your left hand and look at your totally badass thumb. My fist isn't as good for a reference, since i can't bend my thumb that far inwards. :v