Thereafter, {HEAD ~ a pouring aperture} is cut in the barrier layers which span {TAIL ~ the opening} 
Thereafter , { HEAD ~ a pouring aperture } is cut in the barrier layers which span { TAIL ~ the opening }
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL