Located behind front wall 134 is {HEAD ~ a controller}, 140, which controls the opening and closing of {TAIL ~ the apertures} of matrix 138 
Located behind front wall 134 is { HEAD ~ a controller } , 140 , which controls the opening and closing of { TAIL ~ the apertures } of matrix 138
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH