Trepanning

a well known surgical operation. It consists in the removal of a portion of the skull to relieve the brain from pressure. The operation is performed usually with an instrument known as the trepan, crown saw, or trephine. The crown saw consists essentially of a cylinder fastened on a central shaft or pin. The end of the cylinder which is to perform the work is provided with sharp, saw-like teeth. The central pin holds the instrument in position. When twirled between the fingers or driven by power it cuts out a circular piece of bone neatly, making an orifice varying according to the instrument from the size of a dime to that of a silver dollar. If performed with care the wound heals again and no evil results follow. The term is to be distinguished from trapan, sometimes, but less properly, spelled trepan, to take in a trap or snare.