Abstract: A surgical instrument comprising a pair of co-axially assembled tubes having their distal walls in bearing relationship and with registrable openings extending through such distal end and annular walls correspondingly joined to their respective distal walls. The inner tube reversibly rotates within its matched outer tube in operation of the invention, as action by cutting edges formed about such openings severs tissue drawn into the inner tube by suction. Each distal end wall includes a pair of circular cutting edges, those in the inner tube having a straight cut across its thickness while those in the outer tube have a full radiused cut across its thickness. Full radiused cuts across the thicknesses of the annular walls of the inner and outer tubes are provided for arcuately-formed and parallel cutting edges forming the respective openings in these tubes in their annular walls. A method to form these openings by means of these cutting edges is disclosed.