In a preferred embodiment, {HEAD ~ the bottom} of the trough is of {TAIL ~ a convex arcuate shape} over its full width 
is of
In a preferred embodiment , { HEAD ~ the bottom } of the trough is of { TAIL ~ a convex arcuate shape } over its full width
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH