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