In a polygonal rib structure having ribs directed orthogonal to one plane and intersecting each other to form polygonal shapes, {TAIL ~ a thickened central portion} located at a substantially central portion in the longitudinal direction of {HEAD ~ each side} of the polygonal rib is bisected 
In a polygonal rib structure having ribs directed orthogonal to one plane and intersecting each other to form polygonal shapes , { TAIL ~ a thickened central portion } located at a substantially central portion in the longitudinal direction of { HEAD ~ each side } of the polygonal rib is bisected
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH