an elongated axial core element extending in the direction of {TAIL ~ fluid flow} of {HEAD ~ the fluid}, and 
an elongated axial core element extending in the direction of { TAIL ~ fluid flow } of { HEAD ~ the fluid } , and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH