Also, the block has {HEAD ~ the surface} of {TAIL ~ arcuate shape} in cross section at least at a part of its side surface 
of
Also , the block has { HEAD ~ the surface } of { TAIL ~ arcuate shape } in cross section at least at a part of its side surface
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH