The upper inside surface and the lower inside surface of the housing define {HEAD ~ a group} of {TAIL ~ slots} 
of
The upper inside surface and the lower inside surface of the housing define { HEAD ~ a group } of { TAIL ~ slots }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL