Read the full story: Inside a Dry-Aging Room, at A Hamburger Today.
A truck came in toward the end of our visit, so we watched them unload sides of beef. The ceiling-mounted track extends out to the loading dock. The meat packers in charge of unloading the truck have special portable rails that can be attached to the ceiling of the semi trailer and then interface with the existing built-in rail.
Also interesting were the little "switches" on the rail that the meat handlers could use to sidetrack certain sides or move others in.