Each flap can be pulled back from the base member and then can be resecured once {HEAD ~ an instrument} has been inserted between {TAIL ~ the flap} and the base member 
Each flap can be pulled back from the base member and then can be resecured once { HEAD ~ an instrument } has been inserted between { TAIL ~ the flap } and the base member
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH