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