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