{HEAD ~ The rear wall} of the third case in {TAIL ~ communication} with one of the side walls of each of the first case and the second case 
in
{ HEAD ~ The rear wall } of the third case in { TAIL ~ communication } with one 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 TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH