The frame may be rectangular, when each side comprises at least one projection, typically a lug, or {HEAD ~ at least one longitudinal array} of {TAIL ~ loops} 
of
The frame may be rectangular , when each side comprises at least one projection , typically a lug , or { HEAD ~ at least one longitudinal array } of { TAIL ~ loops }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL