Original post-Civil War era medical instrument called a ‘trephine’ used by surgeons in performing operations of the skull. This t-shaped tool allowed the doctor to reduce fractures and to relieve intercranial pressure caused by hemorrhaging. The T-bar ribbon handle is connected to a 2½” metal shaft that has a tapered conical crown of multiple integral sharp cutting blades. Center of the crown features a ‘bayonet’ or pilot drill that can be adjusted in cutting depth by a slide device in the shaft.  Slide device inoperable.  Drill action is powered by twisting the hand and allowing the crown to cut into the skull.  No maker markings visible on instrument. Metal shows flaking of the nickel plating. Cutting crown is rusted and covered with dark oxidation.