. Diseases of the ear; a text-book for practitioners and students of medicine. t even the slightest vestige ofa pneumatic space, with the exception of the antrum, and eventhis may be of small size. Various combinations of these three forms may be metwith in individual cases; thus a sclerotic process may haveprogressed to a certain point and ceased spontaneously, in whichevent the trabecular will be firmer than normal and the pneu-matic spaces of small size; or but one or two air cells may exist,the remaining portion being diploic in structure. Owing to the invariable presence of the mastoid an
. Diseases of the ear; a text-book for practitioners and students of medicine. t even the slightest vestige ofa pneumatic space, with the exception of the antrum, and eventhis may be of small size. Various combinations of these three forms may be metwith in individual cases; thus a sclerotic process may haveprogressed to a certain point and ceased spontaneously, in whichevent the trabecular will be firmer than normal and the pneu-matic spaces of small size; or but one or two air cells may exist,the remaining portion being diploic in structure. Owing to the invariable presence of the mastoid antrum,its location is a matter of importance. It is best located bybearing in mind its relation to the superior and posterior wallsof the external auditory meatus. If two lines be drawn—onehorizontal, tangent to the superior wall of the external audi-tory canal, the second vertical and tangent to its posteriorwall—the point of their intersection will be the apex o\ a tri-angle the base of which will be formed by that portion of the 444 THE ANATOMY OF THE MASTOID Fig. 118.—Horizontal section through a pneu-matic mastoid, s, Groove for lateral sinus ;a, Mastoid antrum ; t, Tympanic cavity ; g,Posterior wall of external canal; iv, w\ Pathof instrument from surface of mastoid toantrum. (Politzer.) curvilinear outline of the meatus included between the pointsof tangency of these lines. This triangle lies immediately over the antrum and anartificial opening withinthis space will enter thecavity. Another cell whichis fairly constant is thatlarge pneumatic spacelocated at the tip of theapophysis. The outerbony wall of this cavityon the digastric surfaceof the mastoid is oftenno thicker than parch-ment, and where the mas-toid is the seat of an in-flammatory process at-tended by the formationof pus, the involvement of this large space may be first evi-denced by the presence of diffuse tumefaction near the mastoidorigin of the sterno-mastoid muscle, either on the external s
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