Some part of mesh won't deform First of all know that I am fairly new to Blender and 3D creation in general.

I got the mesh of an arm, I've done all the rigging and all but I have one problem.

When I parent the mesh and the armature (with automatic weight) all of the fingers armature deform their respective finger of the mesh correctly, except for the index, when I move the index bones the mesh just stays in place.

Someone knows how to fix it? 

Thanks
The automatic weight feature in blender isn't perfect, pretty much every time you use it you will have to go back and manually perfect some weights.

How to fix it:


Hop into to weight paint mode (Click on the UI button that currently says either object or edit mode in the 3D Viewport, and select the Weight Paint Feature)
Open up the current object info tab (The box tab on the same 'tab group' as the render tab) and click on the index finger vertex group.
Use the weight paint brush to change the the effect the bone has on the mesh (Red is full parent and blue is no effect)


Happy Blending!