THE PRODUCTION OF VOCAL SOUNDS I2/ 



middle ear and their attachments to the membrana tympani and the 

 fenestra ovalis. The model shows that when the tympanic membrane 

 to which the handle of the malleus is attached is pressed inwards, 

 the base of the stapes, which fits into the fenestra ovalis, follows the 

 movement ; but when the tympanic membrane is forced outwards 

 beyond a certain point the stapes is not dragged after it, owing to the 

 nature of the articulation between malleus and incus. The model also 

 shows the effect of the tensor tympani in pulling inwards the handle of 

 the malleus and with it the membrana tympani, and the effect of the 

 stapedius in pulling the head of the stapes backwards and causing the 

 base to be tilted within the fenestra ovalis, thus rendering tight 

 the ligament which fixes it in that aperture. 



Semicircular canals. For demonstrating the effects of injury to 

 semicircular canals, a bird (pigeon) is employed. An opening is made 

 in the side of the skull of the anaesthetised animal with a very small 

 trephine, and through the aperture a special instrument is introduced 

 and passed underneath the dura mater until one of the bony semicircular 

 canals (which in the bird project above the surface of the petrous bone) 

 is met with ; the canal can then be broken across. 



For observing the effects of stimulation of the canals in man a strong 

 galvanic current is passed from one side of the head to the other, pad 

 electrodes wetted with strong salt solution being applied in the neigh- 

 bourhood of the ears. The stimulation occurs on the side of the kathode. 



The effects of stimulating the nerve-terminations in the ampullae of 

 the semicircular canals by movements of the endolymph are studied by 

 the aid of a turn-table, upon which the subject (blindfolded) is seated. 

 The several canals are affected according to the inclination of the head 

 the external when the head is erect, the superior with the head inclined 

 forwards, the posterior with the head inclined laterally. On ceasing 

 the rotation varying movements of the body and eyes are produced, 

 involuntary in character and accompanied by giddiness. 



