Abstract: An articulation mechanism has a central part and a head part each made of a pair of shaped elements. The pairs of shaped elements form inner and outer shells. The inner shells are positioned inside the outer shells. The pairs of shaped elements are pivotable relative to one another and lockable relative to one another in several positions in one pivot direction. The outer shells have inwardly oriented projections and the inner shells have openings. A slide is moveably arranged inside the inner shells. The slide has locking members projecting through the openings of the inner shells and engaging intermediate spaces of the projections. A spring acts on the slide in an engagement direction of the locking members relative to the projections. The projections are shaped such that the locking members automatically reach a locking position in a first pivot direction of the head part.