Abstract: An articulation in which a fixed iron member fixedly mounted with a seat frame comprises control means acting on an eccentric member causing upon rotation a locking and respectively an unlocking of a toothed center bearing plate. The toothed center bearing plate has such a shape that when it is pushed on the toothing of the iron member fixedly mounted with the seat frame, it is laterally blocked by reaction thus preventing any lateral displacement even if the mating cooperating toothings comprise some clearance. A rotation pin of the seat back with respect to the seat frame is so shaped that it is supported on two different points on an ovalized bearing member of the iron member fixedly mounted with the seat frame.