THE EAR 



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complete tube, being deficient at the upper and back part, 

 the interval being filled by fibrous tissue. One or two 

 fissures (fissures of Santorini) partially traverse the tube. 

 The inner or osseous part is longer than the preceding, and 

 at its inner end there is a groove round the sides and floor for 

 the insertion of the membrana tympani. In the cartilaginous 

 part of the meatus are hairs and ceruminous glands, which 

 latter secrete the ear-wax. 



THE MIDDLE EAR OR TYMPANUM. 



The tympanum is contained in the temporal bone. It com- 

 municates with the pharynx by the Eustachian tube, and is 

 traversed by a chain of bones, which connect the membrana 

 tympani with the internal ear. 



The cavity of the tympanum is bounded externally by the 

 meatus and membrana tympani, internally by the external 

 surface of the internal ear, and it communicates posteriorly 

 with the mastoid antrum. 



Thereof (tegmen tympani) is formed by a thin plate of bone 

 separating the tympanum from the middle fossa of the skull. 



The floor is formed by the roof of the jugular fossa. 



The outer wall is formed by the membrana tympani and 

 the bone around it ; the following fissures are seen : 



The Glaserian fissure : through which the processus gracilis 

 of the malleus and tympanic branch of internal maxillary 

 artery pass. 



Aperture of the iter chorda posterius : leading to a canal 

 which opens into the aquseductus Fallopii. 



Aperture of the iter chorda anterius : leading to the canal of 

 Huguier, and transmitting the chorda tympani. 



The inner wall presents the following : 



The fenestra ovalis : leading into the vestibule, closed by a 

 membrane and the base of the stapes. 



The ridge of the aquaductus Fallopii : for the facial nerve 

 placed just above the preceding ; posteriorly it passes down- 

 wards and backwards on the mesial aspect of the large opening 

 of the aditus ad annim. 



The promontory : placed below the fenestra ovalis, formed 

 by the projection of the first turn of the cochlea. 



The fenestra rotunda lies at the bottom of a funnel-shaped 

 depression behind the promontory. It is closed by a mem- 

 brane, the secondary membrane of the tympanum of Scarp a, which 

 closes an aperture in the bone leading to the scala tympani 

 of the cochlea. 



