150 ON THE SENSES 



fitted for this purpose, since it gives no direction to the incident waves by wMcb 

 any important portion of them can be thrown into the auditory channel. If we 

 would convert the auricle lato a reflector, we must resort to a very usual means 

 of overcoming any difficulty o£ hearing by bending forwai'd its free cartilage 

 with the hand, while at the same time the hollow palm of the latter is extended 

 to increase the capacity of the cavity. In this way the auricle with the band 

 acts as an ear-trumpet in collecting the waves of sound and throwing them thus 

 condensed into the ear. In its usual posture, on the other hand, the chief ser- 

 vice of the auricle is to be sought in the second of the above-named relations : 

 on the impact of the air-waves, it is itself fitted to take up the vibrations and 

 convey them through the intermediate structures to the tympanum. The com- 

 municated vibrations will, from physical laws, be stronger in proportion, as the 

 direction in which the air-waves strike is more perpendicular, but as the auricle 

 is not a level surface, and, at different points, is struck by the same air-wave in 

 different directions, it is more exact to say that its conducting capacity will be 

 greater, the larger the portion of its surface opposed perpendicularly to the air- 

 wave. If the source of the sound is in front of us, so that the waves are di- 

 rected perpendicularly towards the face, they will evidently strike the right and 

 left ear under equal conditions. In this case it is plain that the ears are not in 

 the most favorable position for the entry of the air- wave into the auditory pas- 

 sages, since, on each side, these cross the direction of the wave at right angles, 

 and there is, besides, a projecting lobe in front which forms a sort of screen to 

 the entrance ; still the auricles are not unfavorably situated as regards the direc- 

 tion of the waves, since a large portion of their cavity is turned almost perpen- 

 dicularly to that direction, at least in persons whose ears stand out somewhat 

 from the head and do not form too small an angle with its side-walls. In this 

 way we may account for the conclusion experimentally arrived at by one of the 

 older physiologists, that the perception of sounds is most distinct if the auricle 

 forms an angle of 40"^ with the lateral surface of the head; the most favorable 

 angle for all directions of sound there are no means of determining. If the 

 source of sound, instead of being before, is on one side of us and in the direct 

 prolongation of one or other of the ear-passages, the conditions are of course 

 different. The ear of the corresponding side has then evidently the advantage, 

 inasmuch as the entrance of the wave into the auditory canal is here direct, 

 while on the averted side it is circuitous ; nor does the auricle, in this case, pre- 

 sent itself in a wholly disadvantageous position to the undulations, since no in- 

 considerable part of its surface, though a different one from the former, is now 

 more or less perpendicular to their direction. That, on the whole, the conditions 

 for the access of the waves are more favorable when they strike the ear laterally 

 rather than directly in front, is evinced by the fact that, in earnest listening, we 

 unconsciously turn the head laterally, so as to bring the axis of one of the 

 auditory canals into the direction of the sound. The above is all that can be 

 said respecting the significancy of the outermost structure of the organ of hear- 

 ing, and is little enough,. if we consider how freely it lies open to observation 

 and the exact knowledge we possess of the nature of the undulations. 



The next part to be traversed by the sound-producing air- wave is the auditory 

 canal ffneatus auditorius externus) which leads from the bottom of the concha 

 or cavity of the external ear to the seat of the finer apparatus of the organ. 

 This canal, which is about an inch long, is not straight, but somewhat bent, nor 

 is it everywhere of equal width ; its walls are covered with the viscous secre- 

 tion called ear-wax, and, especially at the entrance, are overgrown with small 

 hairs. The function of this part, in a general point of view, is clear, though 

 some obscurity rests upon certain special details — that is to say, we know that 

 this external meatus, partly through the included air-column, partly through its 

 own elastic environment, conducts the waves of sound to the interior of the 

 organ ; that on account of its curvature and varying width the waves must, iu 



