{TAIL ~ an open top trough structure} providing {HEAD ~ a pooling space} in which feed material can pool 
{ TAIL ~ an open top trough structure } providing { HEAD ~ a pooling space } in which feed material can pool
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH