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