The blocks of the invention comprise back {HEAD ~ legs} which are directed outwardly from {TAIL ~ the blocks} back surface 
are directed outwardly from
The blocks of the invention comprise back { HEAD ~ legs } which are directed outwardly from { TAIL ~ the blocks } back surface
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH