Furthermore, {HEAD ~ the separation} between {TAIL ~ a pair} of adjacent rows need not be equal to the separation between another pair of adjacent rows 
between
Furthermore , { HEAD ~ the separation } between { TAIL ~ a pair } of adjacent rows need not be equal to the separation between another pair of adjacent rows
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH