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