ABAPTISTON, in Surgery, the perforating part of the instrument called a TREPAN. This instrument, which is mentioned by Galen, Fabricius ab Aquapendente, and others, was a conical saw with a circular edge. Modern practitioners, however, prefer the cylindrical form; and various contrivances have been recommended to obviate the danger that may arise from want of dexterity, or from rashness, in per-
forming the operation of trepanning. The instrument most commonly employed in Britain is the trephine, in which the circular saw is moved backward and forward by the hand; but on the Continent the preference is usually given to the trepan, in which the circular saw is attached to a handle like that of a carpenter's brace; and this is preferred by Professor Syme, and some of our other eminent surgeons, to the trephine, as the latter renders the operation more tedious and laborious. See SURGERY.