A complete roll of wrapping material comprises {TAIL ~ several wrapping portions}, which are held and released at {HEAD ~ their lateral ends} 
A complete roll of wrapping material comprises { TAIL ~ several wrapping portions } , which are held and released at { HEAD ~ their lateral ends }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD