of the inner shell 51 so that the fabric edge 59 wraps onto the back side of the shell and is suitably secured thereto, as by fasteners such as staples or the like.The back assembly 16 also preferably includes a thin flexible covering, such as a fabric 60 positioned so as to overlie the rear surface of the back shell 51, which fabric 60 is preferably interposed between the cushion 58 and the back