Continuing with the previous hand constraint example (and a number of revisions later) here's a collection of information regarding its mesh, bone setup, and constraint rig. It's not intended as a tutorial but should help if your building your own hand and want a quick look at how someone else might have setup the system.
The first image below is a bone mode view of the model mesh, use the colour of each control point to give an idea of which bones control which points. Notice the arrangement of splines at the webbing between each finger. I find this layout the best way to reduce unwanted patch creasing once you have started to animate what must be one of the most awkward sections of a mesh - unless you're trying to make a seamless octopus ;o) Creases are not totally eliminated, but are in roughly the right places for a normal hand and can be made less obvious with careful image decaling (in current versions of Animation:Master use hooks and five point patches to completely remove unwanted creases).
Notice that each joint contains a spline loop controlled by a joint bone to smooth bends. Normally most of the bones you see here are set to hidden, leaving just the bone at the tip of each finger and thumb as this is all that should need to be manipulate. The bone roll handles all point away from the direction of the joint bends, from the below view point they should all point approximately up. The significance of roll handles is that when you come to use spherical constraints, the roll defines the orientation of longitude (ie. values you later use will relate to where the roll handle points).
Below is a hierarchical view of the model bones and some of their pose constraints. Out of all the bones, only the last two at the end of each chain are Attached To Parent (ie. L <finger> middle phalanx and L <finger> distal phalanx). This prevents the inverse kinematic chain from going any further than the knuckle while animating the finger tips. In the pose hierarchic view, only the index finger channels have been expanded, other fingers are configured in the same way as the index finger. Two Orient Like constraints are used on each of the joint bones (Enforce 100%), so that it bends smoothly (with it's assigned spline loop) between the bones controlling the mesh on either side of the joint. Spherical Limits are used keep the fingers bending in a physically realistic manor, with being Longitude being set to Max 0, Min 0, stopping joints from bending sideways. You may wish to set the Longitude limits of the proximal phalanx (bone attached to knuckle) larger so that the fingers can be spread.
As a quick example of the kinds of motion this setup gives your fingers, here's a simple action seen from several views. The hand is not really designed for this dismembered Thing style crawl but for hanging out the end of a sleeve in full character setup; still, it gives an idea of what you can do with this setup. The whole sequence was generated by only moving the ends of the finger IK bone chains. A fully rendered Mac and windows compatible avi of the below motion can also be downloaded here, Hand crawl on black.avi (309Kb)
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