. Manual of operative surgery. erior blade (the blade engaged in the bony opening)to scrape off a thin layer of the cortical bone. This method of using the ron-geur is difi&cult to describe, easy and safe to practice, and aids materially inthe operation. When the mastoid has once been opened to such an extentthat the ronguer can be used efficiently, either as a biting or as a scraping in-strument, put the chisel and mallet aside as of no further use. If muchsclerosis is present, this rule does not apply. Step 4.—No attempt has been made, as yet, to find the antrum or systemat-ically to obliter
. Manual of operative surgery. erior blade (the blade engaged in the bony opening)to scrape off a thin layer of the cortical bone. This method of using the ron-geur is difi&cult to describe, easy and safe to practice, and aids materially inthe operation. When the mastoid has once been opened to such an extentthat the ronguer can be used efficiently, either as a biting or as a scraping in-strument, put the chisel and mallet aside as of no further use. If muchsclerosis is present, this rule does not apply. Step 4.—No attempt has been made, as yet, to find the antrum or systemat-ically to obliterate the mastoid cells; the cortical bone has been removed, at leastto a large extent; the diploe has been but little disturbed. Remember that theantrum in 99 per cent, of cases (Macewen) lies in whole or in part within thesuprameatal triangle; that in the adult its depth beneath the cortical bone variesfrom one-eighth to three-fourths of an inch. With a probe, once more observe the direction and depth of the bony INFECTIONS OF MASTOID 41 With the curette, cautiously remove the cancellous bone from the suprameataltriangle in a direction parallel to the posterior wall of the bony meatus. Thiswill almost inevitably open the antrum. If the bone is much sclerosed, a smallgouge must be used instead of the curette. Having opened the antrum, exploreit thoroughly with a probe. With the curette, aided, if necessary, by rongeurforceps, remove all the external wall of the antrum. In the same mannerremove all the mastoid air-spaces. Every step in the removal of bone must bepreceded by careful examination of the tissues to be removed; remember par-ticularly the normal site of the facial nerve (Fig. 34) and the normal, andparticularly the abnormal, course of the sigmoid sinus.
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