A bone anchor (1) comprising: a first fastening system for fastening a support member to the anchor, and a second fastening system for fastening the anchor to a bone. The second fastening system comprises: first and second clamping jaws (6, 8) defining between them a slot (10) for receiving a bony part of the bone, the second jaw (8) being movable relative to the first jaw (6) so as to clamp the bony part between the first and second jaws, and a locking mechanism (12) for maintaining the second jaw (8) in a fixed clamping position with respect to the first jaw (6).
