{HEAD ~ Recess} 42 in turn comprises channels 44 and {TAIL ~ open portion} 46 
comprises
{ HEAD ~ Recess } 42 in turn comprises channels 44 and { TAIL ~ open portion } 46
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH