an elongated hopper door extending across the full width of {TAIL ~ the box} along the bottom of the hopper to form {HEAD ~ a part} of the bottom thereof 
an elongated hopper door extending across the full width of { TAIL ~ the box } along the bottom of the hopper to form { HEAD ~ a part } of the bottom thereof
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH