{TAIL ~ The nontransparent hollow tube} has inner and outer surfaces that define {HEAD ~ a wall} of the hollow tube 
{ TAIL ~ The nontransparent hollow tube } has inner and outer surfaces that define { HEAD ~ a wall } of the hollow tube
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH