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