This style of case is called a "swing-out". The back is all one piece and the movement swings out on a hinged ring.
This is a hunter case movement, designed for a case that has a pop-open cover. Hunter movements have the seconds dial at 90 degrees from the stem. When they are used with an open-faced case and a normal dial, they are referred to as "side-winders" because the stem is at the 3:00 position. Now and then you see one like this with the seconds dial to the right so that the stem can be at 12:00 like a normal open-faced movement would be.