for thermo expansion of the mantle hanger member 52 after it is secured to the wall 12 referring now to fig9 14 the construction of the upper left corner member 24 is illustrated with specific reference to fig9 and 10 the corner member 24 includes an upper portion 105 and a lower portion 106 the upper portion 105 includes a recessed area 107 having a pair of apertures 108 with brief reference to fig1 each of the apertures 108 is formed within a generally circular recess 110 having a boss portion 112 extending therefrom with continued reference to fig9 11 the corner member 24 includes a top portion 116 which has a u shaped portion 118 depending therefrom the u shaped portion 118 includes a flange 120 having a plurality of spaced apart elongated slots 122 with specific reference to fig1 and 14 the corner member 24 further includes an inner side wall 124 having a cutout portion 126 which has a profile identical to an outer surface 128 of the upper portion 105 of the corner member 24 and further identical to the profile of the front face portion 88 of the mantle molding member 28 shown in fig8 the cutout 126 is further of a size to allow a portion.