LARRY CARTER - I'll answer your question until Steve B sees it and can comment. Those style semi-mounted plows are "Steerable", they pivot off the bar that mounts between the 3-pt hitch lower arms, and that raised rod running to the back "Steers" the rear furrow wheel/tire. The rear hyd cylinder just raises/lowers the tire to put the plow in the ground or raise it, and does nothing to steer the plow.
As tractors got bigger and 4,5, and even up to 8-10-12 bottom plows became common they needed a way to trail better behind the tractors to allow farmers to make small headlands on the ends of the fields. The steerable 4 & 5 bottom plows replaced the pull-type plows and fully mounted plows almost entirely because of the steerable feature. With a little practice you could even back them into corners of fields when plowing headlands and into corners of sheds for storage. Also, because the frt & rear of the plow could be raised/lowered independently, you could keep the headlands more even, getting all bottoms into the ground and turnning furrows at about the same distance from the fence, made plowing headlands much easier. Plowed ground doesn't plow at ALL well the second time, so an even row of furrows entering/leaving the land being plowed made plowing the headlands much easier, and look much better with no missed areas when done.