{HEAD ~ An anchoring means} may optionally be provided at {TAIL ~ the distal end} of the expansion member 
provided at
{ HEAD ~ An anchoring means } may optionally be provided at { TAIL ~ the distal end } of the expansion member
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH