The rear wall of the second case is in {TAIL ~ communication} with {HEAD ~ the rear wall} of the first case 
The rear wall of the second case is in { TAIL ~ communication } with { HEAD ~ the rear wall } of the first case
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH