A bone anchor including 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 includes first and second clamping jaws defining between them a slot for receiving a bony part of the bone. The second jaw is movable relative to the first jaw so as to clamp the bony part between the first and second jaws. A locking mechanism is provided for maintaining the second jaw in a fixed clamping position with respect to the first jaw.
