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ENAMEL. 105

ends of the rods are straight, they will split part way to the dentin (Fig.
87) ; but where they begin to twist round each other they will break
across the rods. If the dentin is removed from under such enamel, it
will break in an irregular way through the gnarled portion.
From a study of the arrangement of the enamel rods in the forma-
tion of the crown it is apparent that the plan is such as to give the
Fig. 87.

Gnarled enamel. (About 50 • .)
greatest strength to the perfect structure, and may be likened to an arch.
At the gino;ival border the rods are short and are inclined apically 6 to 10
centigrades ^ (20° to 35°) from the horizontal plane. These short rods

' In the Centigrade division (he circle
is divided into one hundred parts, each
called a centigrade. One centigrade is
270
equal to 3.6 degrees of the astronomical
circle, 25 centigrades to 90 degrees, 12j
centigrades to 45 degrees. Tlie cut gives
a comparison of the two S3'stems of meas-
uring angles.
180
Centigrade division.