The central surface of the upper side of the cutting head has the form of {TAIL ~ a convexly curved surface} 16, {HEAD ~ the highest position} of which is located at the same level or somewhat below the bottom of the trail 1 a, as best appears in FIG 5 
of
The central surface of the upper side of the cutting head has the form of { TAIL ~ a convexly curved surface } 16 , { HEAD ~ the highest position } of which is located at the same level or somewhat below the bottom of the trail 1 a , as best appears in FIG 5
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH