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