{HEAD ~ The inner passage} 10 and outer passage 11 are separated from one another by an inner tube 16 and are enclosed by {TAIL ~ an outer tube} 17 arranged coaxially thereto 
are enclosed by
{ HEAD ~ The inner passage } 10 and outer passage 11 are separated from one another by an inner tube 16 and are enclosed by { TAIL ~ an outer tube } 17 arranged coaxially thereto
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH