206 . PHYSIOLOGY CHAP. 



motor nerve of the muscle comes from the motor portion of the 

 trigeminus through the otic ganglion. Ludwig and Politzer 

 were able to observe this movement, when the fifth nerve was 

 stimulated at the base of the cranium. 



Helmholtz regarded the tensor tympani as a tightly stretched 

 elastic ligament, the tension of which could be greatly increased 

 by the contraction of the muscle. The effect of this contraction 

 is to make the articulation of the ossicles more rigid and to 

 moderate the vibrations of the tympanic apparatus for loud, deep 

 tones, which obviates undue pressure on the endings of the 

 cochlear nerves. This protective function of the tensor tympani 

 has been compared with that of the sphincter iridis, which as we 



F IG . 79._Course of tensor tympani muscle. 1, Chorda tympani; 2, tendon; 3, tensor tympani; 

 4, septum, dividing belly of muscle from the Eustachian tube ; 5, Eustachian tube ; 6, mem- 

 brana tympani ; 7, tip of manubrium, corresponding with umbus of membrana tympani. 

 /., incus ; pr.br., short process ; pr.l., long process ; pr.len., lenticular process for articulation 

 with stapes. 



shall see limits the number of rays that penetrate the eye, and 

 adapts it to different intensities of light. 



Numerous observations and experiments have been made upon 

 man in health and in disease in support of this theory of the 

 protective functions of the tensor tympani. Destruction of its 

 tendon by disease increases the amplitude of the vibrations of 

 the ossicles, especially in the direction of excursions toward the 

 auditory passage (Bezold). Sometimes after tenotomy the patient 

 complains for many days of hyperaesthesia to high tones of 

 normal strength (Kessel). Helmholtz and Politzer noticed in 

 yawning that hearing was reduced for low tones, which they 

 referred to the associated contraction of the malleus muscle. 

 Some people are able voluntarily to contract this muscle by 

 raising the soft palate. During contraction the low and middle 

 tones are enfeebled, particularly if they are very loud (ISTagel and 

 others). Similar results were obtained on anatomical preparations 



