{HEAD ~ The buffer element} is disposed on {TAIL ~ the lateral wall}, and the lateral side faces the lateral wall 
{ HEAD ~ The buffer element } is disposed on { TAIL ~ the lateral wall } , and the lateral side faces the lateral wall
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH