Well, I don't know the manual steering system as well as a cam rack PS setup (although I should), but the inner rod is the bit that connects the outer steering rods (shaped like an "L") to the steering box arm and idler arm. Those are connected by a big linkage that keeps your wheels pointing in the same direction. Although that big linkage may mount the outer tie rods and itself be the inner tie rod. I'm not quite sure on a 122, and I dropped the whole front crossmember and suspension as a single unit on my scrapped 1800E, so I didn't really take a good look yet.

On a power steering car, the inner tie rods are connected to the outer ends of the steering rack. I had to have several of those serviced and replaced on my 700 and 900 series cars. The 122 is far simpler, but I don't know it as well (because hasn't broken yet and I've got no measurable play in my wheels)