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