Fluid returning to the surface passes through mud return line 14 via various surface equipment components as known to those skilled in the art, and then into {HEAD ~ the mud pits}, thereby completing {TAIL ~ the closed loop} 
Fluid returning to the surface passes through mud return line 14 via various surface equipment components as known to those skilled in the art , and then into { HEAD ~ the mud pits } , thereby completing { TAIL ~ the closed loop }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL