{HEAD ~ An elongate drive shaft} extends from an engine mounted fore of the concavity to {TAIL ~ the impeller} 
extends to
{ HEAD ~ An elongate drive shaft } extends from an engine mounted fore of the concavity to { TAIL ~ the impeller }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL