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 performing the operation of trepanning. A new instrument has been lately invented for this purpose. This instrument is so contrived, that it can be fitted to cut any thickness of bone without danger of injuring the brain; and as no pivot or centre pin is necessary, the dreadful accidents which have sometimes happened by not removing it, when the instrument in common use is employed, are completely avoided. (See Philosoph. Mag. April 1802.)