. Radiography and radio-therapeutics . of the jaw backwards. Thecells usually appear larger in thelower part, and smaller they extend forwards above the articulation of the jaw into thebase of the zygoma. It should be remembered that the cells extend wellbehind the limit of the mastoid process. 4. The petrous bone surrounding the auditory canal, appearing as a densearea superimposed on the mastoid cells. 5. The outline of the lateral sinus should be faintly indicated runningthrough the posterior half of the cells. 6. The foramen magnum, appearing as an elliptical opening with p
. Radiography and radio-therapeutics . of the jaw backwards. Thecells usually appear larger in thelower part, and smaller they extend forwards above the articulation of the jaw into thebase of the zygoma. It should be remembered that the cells extend wellbehind the limit of the mastoid process. 4. The petrous bone surrounding the auditory canal, appearing as a densearea superimposed on the mastoid cells. 5. The outline of the lateral sinus should be faintly indicated runningthrough the posterior half of the cells. 6. The foramen magnum, appearing as an elliptical opening with part ofthe first vertebra crossing it. 7. The outline of the pinna of the ear. Acute mastoiditis shows the following departures from the above description : 1. The air cells are obscured, but can still be faintly seen. 2. The outline of the lateral sinus may be a little more defined than normally. 3. The petrous bone is denser. 4. The whole mastoid region is denser. When one gets an absolutely normal mastoid on one side, and the other. Fic;. 17o.—Position for radiography of themastoitl region by Piries method. 204 KADIOGRAPHY side presents the appearance just described, together with certain clinical signsand symptoms, one is justified in diagnosing acute mastoiditis. Chronic mastoiditis is very typical in a skiagraph. It presents the followingdepartures from the normal : 1. The air cells are completely absent. 2. The petrous bone stands out as a very dense, roughly triangular, areawith its apex pointing upwards and backwards. 3. The posterior border of the petrous bone forms part of a sharp crescent-shaped line. This crescent-shaped line corresponds with the upper and anteriorborder of the lateral sinus. 4. The lateral sinus is frequently very well shown. (2) Radiography of the Sella Turcica.—A useful method for theradiography of the sella turcica has been described by Dr. Finzi. Thepatient is placed upon the couch and the tube centred from below. To deter-mine the exact po
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