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