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