{HEAD ~ The groove} includes {TAIL ~ a central concave portion} and two support surfaces extending downwardly from respective sides of the concave portion 
includes
{ HEAD ~ The groove } includes { TAIL ~ a central concave portion } and two support surfaces extending downwardly from respective sides of the concave portion
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH