Each of {TAIL ~ the side rail portions} of the frame has {HEAD ~ an upright outer wall} and an integral horizontal top wall merging into an inwardly and downwardly slanted inner wall 
Each of { TAIL ~ the side rail portions } of the frame has { HEAD ~ an upright outer wall } and an integral horizontal top wall merging into an inwardly and downwardly slanted inner wall
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH