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