{TAIL ~ Walls} 215 and 216 form two chambers 219 filled with {HEAD ~ air} 
{ TAIL ~ Walls } 215 and 216 form two chambers 219 filled with { HEAD ~ air }
TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD