A pair of parallelly disposed vertical trollies are attached to the side of the building on opposite sides of {HEAD ~ a plurality} of {TAIL ~ emergency exits} 
of
A pair of parallelly disposed vertical trollies are attached to the side of the building on opposite sides of { HEAD ~ a plurality } of { TAIL ~ emergency exits }
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 REL TAIL TAIL TAIL TAIL TAIL TAIL