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