a first rotatable means for controlling {HEAD ~ the horizontal movement} of said cover through {TAIL ~ Said linear means}, 
through
a first rotatable means for controlling { HEAD ~ the horizontal movement } of said cover through { TAIL ~ Said linear means } ,
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH