To create a junction, the portion of {HEAD ~ material} 19 comprises {TAIL ~ a recess} 20 
To create a junction , the portion of { HEAD ~ material } 19 comprises { TAIL ~ a recess } 20
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH