9o 1 lie liar 



the lower the Eustachian tube ; they are separated by the cochleari- 

 form process of bone. Behind the tympanum are the mastoid cells. 



On the inner wall of the tympanum is an oval foramen which is 

 appropriately filled in by the oval plate of the stapes, but which other- 

 wise would open directly into the vestibule. Below this foramen is a 

 round one which leads towards the cochlea, but which is glazed with 

 a threefold layer, like a miniature membrana tympani (p. 97), the 

 innermost layer being the serous lining of the cochlea. Above the 

 oval foramen is a slight ridge which marks the passage of the facial 

 nerve in the subjacent aqueduct of Fallopius. The first turn of the 

 cochlea, bulging outwards, forms a projection, the promontory, upon 

 the inner wall ; and farther back is the pyramid, from the interior of 

 which the stapedius arises. 



After the loss of the membrane the inner wall of the tympanum is 

 clearly shown by otoscopic examination, and Mr. McGill tells of a 

 case in which a minute bubble of air under a film of mucus upon that 

 part which is called the pyramid was for some time mistaken for the 

 glistening head of a pin, which, according to one account, had been 

 pushed into the ear. 



The ossicles. The head of the malleus, or hammer, articulates 

 posteriorly with the incus. Its tapering handle descends vertically 

 between the inner and middle layers of the membrana, the tensor 

 tympani being inserted into its upper end. 



The top of the incus, or anvil, articulates with the head of the 

 hammer. Its short limb passes back to be lodged in the mastoid 

 cells, and the long one runs parallel with the handle of the hammer 

 to articulate, by the os orbiculare, with the head of the stapes, or 

 stirrup, the plate of which blocks the fenestra ovalis. The joints 

 between the ossicles are enclosed in delicate capsular ligaments, lined 

 with synovial membranes, and are liable to attacks of disease. Thus 

 chronic inflammation of the middle ear stiffens them, and so interferes 

 with the oscillation that deafness steadily advances. The subjects of 

 this troublesome complaint hear better when riding in a train or car- 

 riage, as the shaking of the vehicle imparts the needful vibration to the 

 chain. 



The tensor tympani arises from the walls of the bony canal by 

 which it enters the tympanum, and is inserted near the root of the 

 handle of the hammer. It is supplied by a branch from the otic- 

 ganglion. Its action is to draw inwards, and so to tighten the mem- 

 brana ; at the same time it presses upon the perilymph and causes 

 a disturbance of the auditory filaments. When the buzzing in the 

 ear which is supposed to result from this pressure is constant, certain 

 aural orthopaedists have recommended a speculative tenotomy of the 

 muscle. An artilleryman, who is awaiting the firing of a big gun, 

 keeps his mouth open, so that the aerial concussion may rush along 

 the Eustachian tube as well as down the auditory meatus, and that 



