{HEAD ~ The outer perimeter} includes a front perimeter edge and {TAIL ~ a rear perimeter edge} that are joined to each other along a seating axis 
includes
{ HEAD ~ The outer perimeter } includes a front perimeter edge and { TAIL ~ a rear perimeter edge } that are joined to each other along a seating axis
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH