A gap is defined between {HEAD ~ the first edges} of {TAIL ~ sufficient dimension} to accommodate a biomedical instrument 
of
A gap is defined between { HEAD ~ the first edges } of { TAIL ~ sufficient dimension } to accommodate a biomedical instrument
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH