In effect, the flap and base member define {TAIL ~ a receptacle} within which {HEAD ~ the instrument} can be retained 
within retained
In effect , the flap and base member define { TAIL ~ a receptacle } within which { HEAD ~ the instrument } can be retained
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL REL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL