{HEAD ~ The rear wall} of the fourth case is in {TAIL ~ communication} with the other of the side walls of each of the first case and the second case 
is in
{ HEAD ~ The rear wall } of the fourth case is in { TAIL ~ communication } with the other of the side walls of each of the first case and the second case
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH