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