The vessel and the seal cover have respective surfaces that, when engaged, define {HEAD ~ a circumferential interior passage} between the vessel and {TAIL ~ the seal cover} 
between
The vessel and the seal cover have respective surfaces that , when engaged , define { HEAD ~ a circumferential interior passage } between the vessel and { TAIL ~ the seal cover }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL