The two passages 10, 11 are arranged coaxially to one another, so that {HEAD ~ the outer passage} 11 encloses {TAIL ~ the inner passage} 10 
encloses
The two passages 10 , 11 are arranged coaxially to one another , so that { HEAD ~ the outer passage } 11 encloses { TAIL ~ the inner passage } 10
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH