THE AUDITORY APPARATUS 211 



causing little swelling, give rise to severe pain. Chronic in- 

 flammatory processes may stimulate the periosteum to such an 

 extent that the new bone may occlude the canal almost entirely. 

 The cuticular lining is supplied by branches from the auriculo- 

 temporal nerve (p. 174) and the auricular branch of the vagus. 

 Stimulation of the latter nerve, by foreign bodies or collections 

 of wax, may produce symptoms so divergent as cough (internal 

 laryngeal nerve, p. 159) and dyspepsia (terminal branches of 

 vagus, p. 298). Similar irritation of the auriculo-temporal 

 nerve gives rise to pain, which may be referred to the side of 

 the head, to the teeth of the mandible, etc. 



The cuticular lining of the canal possesses numerous cerumin- 

 ous glands ; and the wax which they secrete is normally carried 

 to the exterior by the movements of the mandibular condyle, 

 which presses against the anterior wall of the meatus. Sudden 

 deafness sometimes follows the entrance of water into the canal, 

 as it is readily absorbed by the wax, which swells up in con- 

 sequence. 



The Membrana Tympani lies at the bottom of the external 

 acoustic meatus, and forms the greater part of the lateral wall 

 of the tympanic cavity. It consists of an outer cutaneous, an 

 inner mucous, and an intermediate fibrous layer. It is very 

 obliquely placed, so that its outer surface looks laterally, down- 

 wards and slightly forwards, i.e. the antero-inferior portion is 

 furthest removed from the surface. 



When a normal tympanic membrane is examined with the 

 aid of reflected light, a well-marked depression, the umbo, can. 

 be recognised at a little below its centre. When the auditory 

 tube is obstructed the air in the tympanum becomes absorbed, 

 and the normal concavity is accentuated. The handle of the 

 malleus, which is attached to the fibrous layer of the membrane, 

 can be traced upwards and forwards from the umbo to a small 

 prominence, which is produced by the lateral (short) process 

 of the malleus. From this point the anterior and posterior 

 malleolar folds diverge in an upward direction, and bound the 

 flaccid part of the membrane (Fig. 64). The cms longum (long 

 process) of the incus may be discerned lying behind and parallel 

 to the handle of the malleus, though it lies on a deeper plane. 

 A cone of reflected light extends from the umbo over the antero- 

 inferior part of the membrane, and serves as a guide to the site 

 of puncture in the operation of paracentesis tympani, which is 

 carried out through the postero-inferior quadrant. This part of 



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