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