I was told (can't remember by who) that it takes alot of natural raw food to get them the glucosamine they need, so I started supplementing again because I have one dog with an intermittent limp that could be arthritis.
But, I do feed alot of chicken feet and heads and rabbit heads.
I definitely consider a chicken foot mostly bone - I cut a toe off for Snorkels but I do it with those meat scissors. It sure feels like bone to me. In fact, it feels like a big giant bone wrapped around some skin. But when you get in there, there are some blood vessels and ligaments going down the toes.
Edited to add: I tried to crush a chicken foot with a hammer once. I had to go onto the sidewalk, onto concrete, and pound like crazy. They are hard as rocks. Gave me more admiration for what my dog's teeth can do, when he chomps 2-3 times and the are crunched up.