Yes! That's all you need
The finger parts? on a bat they are exactly that, the felanges bones, which in a human are our fingers.
In order to get those, just build 2-4 more 'finger bones'. They will attach at the same point as the top hinging outer 'finger bone'. You won't need to wire or harness them so long as you use some kind of fabric membrane between the outer 'finger bone' and the inner wrist/ elbow short 'bones'. The fabric itself will serve that purpose.
If you are having a hard time conceptualizing this, try the following experiment (nothing permanent, so any materials will do)
Get a pillow case, your sewing pins, and a couple wire hangars.
Slip the hangar inside the pillow case putting the flat straight bottom wire into the square end of the pillow case. Pin it so it won't slip out.
Pick it up by the wire end and wave it around, you'll notice the pinning of the hangar controls the fabric.
Slip the second wire hangar in the pillow case, flat bottom end up against a side seam, sliding it up to where the two hangars are almost touching each other.
Pin so that the hangars are not attached to each other.
Hold the side seam hangar and wave it around. If you hold it right at the corner, you should be able to manipulate an opening and closing motion with one hand.