My rear derailler attaches in the dropout directly where the wheel does. The bolt for the rear wheel is what holds the derailler on. This makes it pretty annoying to change the rear tire. It almost takes more than 2 hands to simultaneously hold the derailler (keeping tension on the spring), holding the rear wheel straight, and tightening the bolt.
I've gotten pretty good at it, but I'm wondering: is this the way the bike was designed, or am I missing a part? I don't see anywhere else the derailler hanger could bolt on.