The frame includes a front surface (10) that is extended by two side tenons (12) and two arms (30) that are hinged onto the tenons (12) about the hinge axes (X-X') of two hinges (50). The hinges (50) each include a front surface element (51) that rigidly connected to a tenon (12) and an arm element (52) that is rigidly connected to an arm (30). Each arm (30) is set up such as to pass, through rotation about said hinge axis (X-X'), from an open position for which said arm extends the tenon (12) to a closed position for which said arm is clamped into the front surface (10). In at least one of the hinges (50), the hinge axis (X-X') is substantially perpendicular to the tenon (12) and to the arm (30). The front surface element (51) and the arm element (52) are set up such as to provide, between said tenon (12) and said arm (30), a space (60) for freely passing from the open position to the closed position.