THE EAR. 



89 



to the opening of the Eustachian tube is an elevation on the internal wall called the 

 promontory, formed by one of the semicircular canals. Above the promontory is the 

 fenestra ovalis, which lodges the stapes bone and communicates with the vestibule. 

 Below and behind is the fenestra rotunda, closed by a membrane separating the 

 cochlea from the middle ear. Above the fenestra ovalis is a ridge of bone marking 

 the aqueduct of Fallopius, in which runs the facial nerve. 



The Eustachian tube passes from the anterior portion of the tympanic 

 cavity downward, forward, and inward to the upper posterior portion of the pharynx 

 about level with the floor of the nose. It is about 3.5 cm. (approximately i^ in.) 

 in length. The outer third, near the ear, is bony and the inner two-thirds are 

 cartilaginous. The point of junction of the bony and cartilaginous portions is the 

 narrowest portion of the tube and is called the isthmus. The tube is usually closed, 

 but opens in swallowing, yawning, etc., thus admitting air to the tympanic cavity 

 and mastoid cells. Catarrhal affections of the throat readily travel up the tube and 

 set up an inflammation of the middle ear. Swelling of the lining of the tube follows 

 and air no longer passes to the ear. To open the tube two methods are employed 

 that of Valsalva, and that of Politzer. The former consists in holding the nostrils and 

 mouth shut and attempting to blow, when the action of the throat and palate muscles 

 opens the tube and allows the air to enter. In the method of Politzer, the patient is 



Tegmen tympani 



Chorda tympani nerve 



Long handle of malleus 



Tensor tympani muscle 



Incus 



Tympanic membrane 



Eustachian tube 



Stapes 

 FIG. 104. View of the tympanic membrane and ossicles of the left ear from within. 



given a sip of water which he swallows on command. The nozzle of a rubber air-bag is 

 placed in one nostril and the other held shut. As the patient swallows, the air-bag is 

 compressed and the air enters the Eustachian tube. Sometimes this method is varied 

 by asking the patient to say ' 'hock, ' ' thus causing the tube to open, when the air-bag is 

 compressed. The calibre of the tube is sometimes so small that probes are passed 

 up it to dilate it. Care is necessary to avoid introducing the probe too far or it will 

 injure the ossicles of the ear. Pus will sometimes discharge through the tube. I 

 have seen pus coming from the middle ear pass down the tube into the inferior 

 meatus and be blown out the anterior nares. 



Lying in a separate canal immediately above and parallel with the Eustachian 

 tube is the canal for the tensor tympani muscle. 



The attic is directly above the tympanic cavity and contains the greater part of 

 the ossicles. Between the two along th<" ' ner wall runs a ridge of bone within which 

 is the aquaeductus Fallopii, containing the facial nerve. The roof of the attic is called 

 the tegmen. It is a thin shell of bone, varying in thickness, and separates the cavity 

 of the ear from the middle cerebral fossa above. Pus frequently eats its way through 

 at this point and forms a subdural abscess, which by working its way backward 

 involves the lateral (transverse) sinus, causing thrombosis and general septic infection. 



