{HEAD ~ The toothed arch block} has one end disposed in {TAIL ~ contact} with the arched notch 
{ HEAD ~ The toothed arch block } has one end disposed in { TAIL ~ contact } with the arched notch
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH