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