Quadrans Muralis, or the Mural Quadrant, is an obsolete constellation that was located between Draco, Hercules and Bo÷tes. It is primarily of interest today because a meteor shower (the Quadrantids) is named after it. A mural quadrant is a device mounted parallel to the celestial meridian to accurately observe the altitudes of stars. An illustration of Tycho Brahe's mural quadrant is shown below.
Historical Map of Quadrans Muralis
From Bode's 1801 Uranographia (Image Credit and © Tartu Observatory Virtual Museum; used by permission)