Could be one for one of our resident butchers.
I just saw a cooking show where they slow cooked a conical muscle, but I missed the full description of where the muscle is from. I did hear it was near a tendon and I got the impression it's a shin muscle. They were saying using this muscle is ahead of the market, like back when beef cheeks were cheap before everyone else found out about them.
It's definitely a working muscle which sounds like has a gelatine feel when cooked, it was compared to cheeks. Apparently the best place to get it is Asian butchers.