One is a genius, the other's insane, they're laboratory mice, their genes have been spliced, they're Pinky, they're Pinky and the Brain Brain Brain Brain Brain.
At the moment the thumb and pinky come out at around at a near-parrallel 180 degree angle which is impossible. Here's a tip, if you have a webcam, make that pose with your hand and take a photo of it, then draw alongside it, or use the one from the show itself.
Oh yeah, and well done on the drawing, everybody give that man a hand! (arf.)