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