{TAIL ~ The concavity} has a minimum depth at its leading end and a maximum depth at {HEAD ~ its trailing end} 
{ TAIL ~ The concavity } has a minimum depth at its leading end and a maximum depth at { HEAD ~ its trailing end }
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD