Rig bending fingers help!

Character.blend (1.08 MB) I hope this is working correctly…If anyone could look at the rig, he has fingers…If you bend those fingers and go into wireframe viewport thing, you see theres some weird thing going on the back of the finger. I dont know what it is, as I found the rig online. But I really need to figure it out…If you can, help me and also post a tutorial if possible!
Thank you very much
Tahu.