. Diseases of the ear : a text-book for practitioners and students of medicine. e tympanum the contents of the middlecranial fossa is usually involved. The internal surface of the mastoid process presents a deepgroove for the lodgment of the lateral sinus. The distancewhich this vessel may extend into the mastoid varies in indi-vidual cases ; usually it lies be-hind the antrum, and in someinstances the bend of the sinusis so sharp that the acute angleextends forward so as to lie buta short distance behind the pos-terior wall of the external audi-tory meatus, and may be so nearthe surface of th
. Diseases of the ear : a text-book for practitioners and students of medicine. e tympanum the contents of the middlecranial fossa is usually involved. The internal surface of the mastoid process presents a deepgroove for the lodgment of the lateral sinus. The distancewhich this vessel may extend into the mastoid varies in indi-vidual cases ; usually it lies be-hind the antrum, and in someinstances the bend of the sinusis so sharp that the acute angleextends forward so as to lie buta short distance behind the pos-terior wall of the external audi-tory meatus, and may be so nearthe surface of the process as tocover the antrum (see Fig. 120).It is evident that with the sinusin this position an artificial open-ing into the antrum could notbe made at the site of electionfor entering this cavity withoutexposing or wounding this largevenous channel. In Fig. 118 the parts are so placed that thesinus is in no danger, while in Fig. 119 it could be avoidedwith care. An examination of numerous specimens has been madeby both Korner ^ and Randall f for the purpose of determin-. FiG. 120.—/, Tympanic cavity; u,Floor of external meatus ; s, Gioovefor lateral sinus ; 7a, w, Path of in-strument from surface of mastoid toantrum. In this case the sinus wouldbe wounded in the operation. (Po-litzer.) * Arch, of Otol., vol. xviii, p. 310. \ Trans, of the Amer. Otol. Society, 1892, p. 235. 436 THE ANATOMY OF THE MASTOID PROCESS. ing- whether the location of the sinus could be positively de-cided by external measurements of the skull. These re-searches prove conclusively that external measurements areuseless in determining the site of the sinus. This venouschannel, then, bears an important relation to the mastoid pro-cess, and its variable situation must always be borne in mindin operative procedures. When, for any reason, it seems de-sirable to expose the sinus during an operation, it can be doneby extending the opening in the bone backward, care beingtaken to avoid the removal of any bo
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