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