A smoothly arched notch extends axially to {HEAD ~ the topmost edge} of {TAIL ~ the box end} 
of
A smoothly arched notch extends axially to { HEAD ~ the topmost edge } of { TAIL ~ the box end }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL