its teeth makes only a
narrow incision,[A] it should, while operating, be kept well oiled, and
should be withdrawn every few seconds in order that the horn-dust lying in
its teeth may be examined. If this is getting slightly blood-stained,
we know, of course, that the sensitive structures are reached, and the
incision has been carried far enough. In so judging the depth of the
incision, however, care must be taken to see that the top of the coronary
cushion is not injured with the saw, for if this is done the blood
trickling into the depth of the incision will tinge the horn-dust, and give
the false impression that the incision is sufficiently deep.

[Footnote A: That is Smith's older pattern. The newer pattern (Fig. 145)
has the teeth so set as to make an incision wide enough to be looked into.
In this case the depth arrived at is to be judged by the appearance of the
bottom of the incision.]

If the operator has had no previous experience of the use of the saw in
this operation, he must also be careful to avoid placing too great a
pressure on the teeth of its lower third. This is done by keeping the hand
too greatly depressed. Again, this leads to wounding of the sensitive
structures (this time at the lower end of the incision), and again the
operator is confused by the blood thus allowed to run into the groove.

The only portion of horn difficult to operate on is that immediately under
the coronet. This is best severed with a succession of downward movements,
and is easier performed with Smith's later pattern of side-bone saw (Fig.
145) in which the set of the foremost teeth is reversed.

[Illustration: FIG. 145.--SMITH'S SIDE-BONE SAW (IMPROVED PATTERN).]

In making these grooves we must say that we think the use of the special
saw may be dispensed with, and the incisions just as easily, or, at any
rate, just as successfully, made with the knife. Those who select to use
this instrument should choose a narrow-topped and sharp searcher, or a
modern shaped drawing-knife of suitable size, such as those depicted in
Fig. 46, _a_ and _b_, and they will find their work much easier if
they will make the first steps in the incisions with an ordinary flat
firing-iron. By the use of the latter instrument the grooves are made
conveniently open along their tops, and room left for nicely finishing the
more delicate manner of removing with the knife the softer horn near the
sensitive structures.

Those whose leaning is toward