1 152 THE EAR. 



downwards and outwards. Since the osseous portion of the meatus runs from 

 above downwards and inwards, it is evident that, if glands existed in this 

 portion, the cerumen would collect around the tympanic membrane, with 

 a result disastrous to the transmission of sound. 



The outward flow of cerumen is also aided by the continually repeated 

 movements of the cartilaginous meatus which occurs during mastication. 



Movements of the auricle. The movements of the auricle in the 

 human being are for the most part insignificant. They have no effect 

 on hearing. The muscles of the tragus and antitragus tend to contract 

 the orifice of the meatus, while those of the helix produce the opposite 

 effect. Many animals have the power of moving the opening of the 

 auricle in the direction from which the sound conies. Thus the horse 

 pricks its ears when it hears a sound, and no doubt its appreciation 

 of the direction of sounds is thereby assisted. 



Though none of the muscles of the pinna are, as a rule, under the 

 control of the will, yet some individuals have the power of moving that 

 structure as a whole. No doubt, by attention and practice, a man may 

 acquire the power of moving the auricle slightly; but at best these 

 movements are small as compared with those of the lower animals. 

 Politzer 1 states that an unconscious movement of the ear occurs in 

 many persons when they listen to a very feeble noise. In some animals 

 a reflex contracture of the muscles of the pinna occurs when the ear is 

 suddenly stimulated by sound. 



THE MIDDLE EAR. 



The function of the middle ear is to receive sound-waves occurring 

 in the air, and to transmit the effect of these to the labyrinth. The 

 reception of the waves naturally comes first under consideration, and, 

 since the tympanic membrane is the only structure concerned in this 

 part of the process, an accurate knowledge of its anatomical structure, 

 position, and tension in the living being are necessary for a full appre- 

 ciation of its important function. 



The tension of the membrana tympani, and its regulation. 

 Although, as a matter of fact, the membrana tympani is a stretched mem- 

 brane, yet, from the acoustic point of view, it does not act like the mem- 

 brane of a drum. If it did so act, waves of sound would cause it not only 

 to vibrate, but to continue vibrating after the tone had ceased, and thus 

 confusion and indistinctness of the sound would result. The membrane 

 is also perfectly elastic in all its parts, although the amount of 

 movement of various parts is not the same, owing chiefly to the 

 fact that the relative number of radiating and circular fibres varies in 

 different parts. Thus the central portions are composed almost entirely 

 of radial, while the peripheral parts are formed chiefly of circular fibres. 

 If the air in the external meatus be rarefied and condensed alternately 

 by means of a pneumatic speculum, it will be observed that certain 

 parts of the membrane undergo much greater alterations in position 

 than others. Mach and Kessel 2 first demonstrated that this change in 

 position of the membrane was greatest in the posterior segment. 



Some writers have asserted that the membrane has a tone of its own. 

 Thus Politzer 3 names the tone as e* (mi*), having a vibration frequency 



1 Op. tit., p. 56. 



2 Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1874, Bd. Ixix. S. 221. 



3 Op. cit., p. 58. 



