Anchor for attachment to a bony structure, comprising a hook, an anchor body with a distal wall facing the hook, and a fastening system for fastening a connection member to the anchor body. A slot is defined between the hook and the distal wall, for receiving a bony structure such as a vertebra portion. The anchor further comprises a retention member having a distal end with teeth, passing through the distal wall and being movable relative to the anchor body, from a retracted position to a protracted position where the distal end protrudes from the distal wall, inside the slot. The proximal end of the retention member defines a seat for the connection member.
