an endless linear means for moving said cover which is connected to {HEAD ~ opposed side portions} of {TAIL ~ the cover}, 
an endless linear means for moving said cover which is connected to { HEAD ~ opposed side portions } of { TAIL ~ the cover } ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH