202 THE ORGANS OF SPECIAL SENSE 



gradual absorption of the air in the middle ear, and, as the 

 atmospheric pressure on the outside of the membrane is un- 

 opposed, the membrane is bulged medially. Under these 

 circumstances, the conduction of sounds to the internal ear 

 is gravely disturbed. Artificial inflation of the middle ear, 

 whether by Valsalva's method or by means of a Eustachian 

 catheter (p. 329), is carried out for the purpose of equalising 

 the pressure on the two sides of the tympanic membrane. 



In its medial part, the anterior wall separates the middle 

 ear from the canal which contains the internal carotid artery. 

 Cases have been recorded in which this portion of the wall 

 has become necrosed, following otitis media, and the patient 

 has died from the resulting haemorrhage. 



The posterior wall of the middle ear communicates with the 

 tympanic (mastoid} antrum through an opening situated in its 

 upper part. Suppurative processes beginning in either of the 

 two cavities soon spreads to involve the other. 



The lateral wall of the middle ear is formed by the 

 tympanic membrane and, above its upper border, by a small 

 part of the squamous portion of the temporal bone. 



The Tympanic Membrane consists of three layers, which 

 form an outer cuticular, a middle fibrous, and an inner 

 mucous stratum. It presents a very intimate relation to the 

 malleus^ the head of which, however, lies in the epitympanic 

 recess (attic) above the level of the membrane. The handle 

 of the malleus passes downwards and slightly forwards between 

 the fibrous and mucous strata, and its outline can be deter- 

 mined on otoscopic examination. At its upper part, the 

 handle of the malleus is crossed by the chorda tympani 

 nerve (p. 84), which emerges from a small canal in the 

 posterior wall and passes forwards to the anterior border of 

 the membrane, where it enters another canal, which conducts 

 it to join the lingual nerve (p. 75). 



On OTOSCOPIC EXAMINATION the handle of the malleus can 

 be distinctly seen, and from its lower end, which lies a little 

 below the centre of the membrane, a "cone of light" passes 



