868 THE ORGANS OF SPECIAL SENSE. 



the anterior wall is separated from the temporo-mandibular joint and parotid gland by the bone 

 forming the glenoid fossa ; and the posterior wall is in relation with the mastoid cells ; hence 

 inflammation of the external auditory meatus may readily extend to the membranes of the 

 brain, to the temporo-mandibular joint, or to the mastoid cells ; and, in addition to this, blows 

 on the chin may cause fracture of the waif of the meatus. 



The nerves supplying the meatus are the auricular branch of the pneumogastric, the 

 auriculo-temporal, and the auricularis magnus. The connections of these nerves explain the 

 fact of the occurrence, in cases of any irritation of the meatus, of constant coughing and sneez- 

 ing from implication of the pneumogastric. or of yawning from implication of the auriculo- 

 temporal. No doubt also the association of earache with toothache in cancer of the tongue is 

 due to implication of the same nerve, a branch of the fifth, which supplies also the teeth and 

 the tongue. The vessels of the meatus and membrana tympani are derived from the posterior 

 auricular, temporal, and internal maxillary arteries. The upper half of the membrana tympani 

 is much more richly supplied with blood than the lower half. For this reason, and also to avoid 

 the chorda tympani nerve and ossicles, incisions through the membrane should be made at tfie 

 lower and posterior part. 



The principal point in connection with the surgical anatomy of the tympanum is its relations 

 to other parts. Its roof is formed by a thin plate of bone, which, with the dura mater, is all that 

 separates it from the temporal lobe of the brain. Its floor is immediately above the jugular 

 fossa behind and the carotid canal in front. Its posterior wall presents the openings of the 

 mastoid cells. On its anterior wall is the opening of the Eustachian tube. Thus it follows 

 that in disease of the middle ear we may get subdural abscess, septic meningitis, or abscess of 

 the cerebrum or cerebellum from extension of the inflammation through the bony roof: throm- 

 bosis of the lateral sinus, with or without pyaemia, by extension through the floor ; or mastoid 

 abscess by extension backward. In addition to this, we may get fatal hemorrhage from the 

 internal carotid in destructive changes of the middle ear ; and in throat disease we may get the 

 inflammation extending up the Eustachian tube to the middle ear. The Eustachian tube is ac- 

 cessible from the nose. If the nose and mouth be closed and an attempt made to expire air, a 

 sense of pressure with dulness of hearing is produced in both ears, from the air finding its way 

 up the Eustachian tube and bulging out the membrana tympani. During the act of swallowing, 

 the pharyngeal orifice of the tube, which is normally closed, is opened, probably by the 

 action of the Dilator tubea muscle. This fact was employed by Pphtzer in devising an easy 

 method of inflating the tube. The nozzle of an india-rubber syringe is inserted into the nostril ; 

 the patient takes a mouthful of water and holds it in his mouth ; both nostrils are closed with 

 the finger and thumb to prevent the escape of air, and the patient is then requested to swallow ; 

 as he does so the air is forced out of the syringe into his nose, and is driven into the Eustachian 

 tube, which is now open. The impact of the air against the membrana tympani can be heard, if 

 the membrane is sound, by means of a piece of india-rubber tubing, one end of which is inserted 

 into the meatus of the patient's ear, the other into that of the surgeon. The direct examination 

 of the Eustachian tube is made by the Eustachian catheter. This is passed along the floor of 

 the nostril, close to the septum, with the point touching the floor, to the posterior wall of the 

 pharynx. When this is felt, the catheter is to be withdrawn about half an inch, and the point 

 rotated outward through a quarter of a circle, and pushed again slightly backward, when it will 

 enter the orifice of the tube, and will be found to be caught, and air forced into the catheter 

 will be heard impinging on the tympanic membrane if the ears of the patient and surgeon are 

 connected by an india-rubber tube. 



