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