Wall 31 has formed therein {HEAD ~ a hole} 32 bounded by {TAIL ~ a circumferential margin} 33 provided by wall 31 
bounded by
Wall 31 has formed therein { HEAD ~ a hole } 32 bounded by { TAIL ~ a circumferential margin } 33 provided by wall 31
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH