said corrugations, said concave portions adjacent thereto, and said {HEAD ~ intermediate flat portions} being located sequentially along {TAIL ~ the axis} of the pipe 
located sequentially along
said corrugations , said concave portions adjacent thereto , and said { HEAD ~ intermediate flat portions } being located sequentially along { TAIL ~ the axis } of the pipe
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH