There is a full opening with {HEAD ~ an absence} of {TAIL ~ a top wall} providing a top wall edge 113 which makes the top edges of the fore and aft end walls and the two angled sidewalls 
There is a full opening with { HEAD ~ an absence } of { TAIL ~ a top wall } providing a top wall edge 113 which makes the top edges of the fore and aft end walls and the two angled sidewalls
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH