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