A {HEAD ~ ledge} or {TAIL ~ mandible engaging support surface} is defined between the upper tier and lower tier and terminates in an exterior opening 
A { HEAD ~ ledge } or { TAIL ~ mandible engaging support surface } is defined between the upper tier and lower tier and terminates in an exterior opening
OTH HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH