Basic Houdini introduction:
Rigging a quadruped in Houdini 16.5
link 2 hour Houdini rigging course!
Houdini 16 leg rig:
Various constraints:
Rigging a hand:
Blendshapes:
Capturing/Skinning:
Basic Houdini introduction:
Rigging a quadruped in Houdini 16.5
link 2 hour Houdini rigging course!
Houdini 16 leg rig:
Various constraints:
Rigging a hand:
Blendshapes:
Capturing/Skinning:
Bjørn Blaabjerg 
This is an excellent resource for learning about the basics of quadruped riggings in Houdini.