It was an arduous effort, but I think I've finally fixed the topology of the paw. Well, mostly anyways. There's still one or two oddities, but nothing that is seriously impacting the deformation.

Countless revisions, numerous experiments, endless adjustments. The effort that went into this was at least as great as the retopology of that hand, albeit a bit more successful, I think.

The biggest change is one of the earliest; I added 3 helper joints in between the digits, closer to the paw pad. This changes the way paw deforms when I move the skinned model from the modeling and weight-painting pose, into the more natural pose that puts the digits together. Each digit is composed of 2 bones, similar to the fingers minus one joint. The first joint, equivalent to the knuckle on the fingers, is within the model and above the paw pad. This first joint was almost exclusively used to solely for rotating the adducting digits towards the paw medial. There were a few other slight rotations used for posing, but the majority of digit posing was accomplished by the second joint of the digit.

Along with bringing its digit into alignment, that first joint of each digit would also pull a piece of the paw pad into alignment. Originally, I didn't have a paw pad (it was planned as more of a textured feature) but during the previous revision, I started to give the paw pad a physical presence. This conflicted with the first joint deforming it because I simply couldn't produce a workable shape out of the deformation. It would be creased, or out of position or not hold a pleasing shape. It looked terrible. The 3 helper joints serve as a counter to the first digits, and lock the paw pad in place, so that I'm free to designate its shape properly.

Well, that was the idea, anyways. It became very clear that the actual topology itself was still going to introduce creases. It took a very long time to come up with a solution that solved that. So long, that I didn't even get to do the reshaping I wanted to! But, I finally found a workable topology for this very complex area that doesn't have any 6-edge vertices or triangles, or tris in the places that would hurt deformation or shape.

There was a whole bunch of other topology work on the area that serves as the ball of the foot and the connections of the digits. There was one change that seemed to allow me to eliminate an edge on the outermost digits that would let me keep the "Three edges for a curve" on top. That one was very promising, because it let me eliminate an extra tri and diamond on the backside of the foot. Long after I implemented it, however, as I was searching for something to solve another issue with the paw pad, I discovered that this 'ideal' arrangement actually caused the 4 separate vertical edgeloops of those digits to become one long spiral edgeloop! Complications...

But, all that's solved now and I can finally focus on the shape of the paw again! The changes were so extensive that they inadvertently introduced shape changes on their own.