A coupling element (28) joins two placement elements (18,20) so that bone-plates (10,12) are fixed between the two placement elements. Relative movement between the coupling element and the second (20) element crosswise to the direction in which the bone-plates are clamped causes the bone-plates to be fixed between the two placement elements. The first and or second placement element has/have a holder fitting into the gap (14) between the adjacent bone-plates.