introducing the second member of the first pair and {HEAD ~ the first member} of the second pair into {TAIL ~ a second vessel} from the first vessel 
into
introducing the second member of the first pair and { HEAD ~ the first member } of the second pair into { TAIL ~ a second vessel } from the first vessel
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH