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