DISEASES OF THE LATERAL CARTILAGES 373 
that portion of horn forming the outer boundary of the 
cutigeral groove, and accommodating the coronary cushion. 
For the making of the incisions there is the special saw 
devised for this operation by Colonel F. Smith, A.V.D., and 
which we illustrate in Fig. 144. With this the wall is sawn 
through until the depth arrived at is equal to what is indi- 
cated by a previous examination of the thickness of the crust 
as viewed from the solar surface. Here Colonel Smith says: 
‘I strongly advise everyone to use a metal gauge (a thin 
piece of material) to introduce into the incision made by the 
saw, and run it up and down to ascertain whether the wall 
is properly divided throughout. The depth to which this 
should be done we know from the previous measurements 
of our gauge on the crust.’ 
Fic. 144.—Smurra’s Sipe-Bone Saw (Harty Parrery). 
Should the saw be of a pattern in which the set of its 
teeth makes only a narrow incision,* it should, while opera- 
ting, be kept well oiled, and should be withdrawn every few 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 bloodstained, 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. 
If the operator has had no previous experience of the 
use of the saw in this operation, he must also be careful to 
* 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 
