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