{HEAD ~ The gas} and vapor evolved in these zones passes upwardly through the vents 94 into {TAIL ~ the vapor collection region} 89 and is removed 
passes upwardly into
{ HEAD ~ The gas } and vapor evolved in these zones passes upwardly through the vents 94 into { TAIL ~ the vapor collection region } 89 and is removed
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH REL REL OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH