ii5o THE EAR. 



hunting-horn, is inserted into the meatus in such a way that its wide opening 

 is directed backwards to the concha, hearing is assisted, the sound-waves which 

 strike the concha being reflected upon the instrument, which then directs 

 them inwards. 



A more delicate mode of testing this question is to sound a compound tone, 

 and observe whether it changes in quality, according to its position in relation 

 to the ear. Thus, if the auricle reflects the fundamental tone more strongly 

 than the partials, or the converse, then a change in the quality of the tone 

 should be perceptible when alterations are made in the position of the source 

 of sound. Experiment shows that such a difference in quality is found to 

 occur. Thus S. P. Thompson 1 has pointed out that the ticking of a watch placed 

 in the middle line behind the head appears to have a slightly different quality 

 from that which it possesses when held in the corresponding position in front 

 of the head, the higher tones being relatively more pronounced in the former 

 case. Gray 2 has found that by putting the hand in front of the ear, with tbe 

 hollow of the palm directed backwards, while the watch is behind the head, 

 the relative increase in the intensity of the higher tones is annulled, and the 

 sound has the same quality as when held in front of the head. 



Mach 3 has suggested that the pinnae may act as resonators for the higher 

 partials of compound tones. S. P. Thompson 4 is of opinion that the cartila- 

 ginous rim at the outer margin of the pinna may catch sound-waves that have 

 been reflected from the ground in an upward direction. Politzer 5 asserts that 

 not only the concha but also the tragus exercises a certain influence upon sound- 

 waves. By placing a small disc behind the tragus, and thus directing its apex 

 outwards, he found that acuteness of hearing was appreciably increased. This 

 increase he attributes to the larger surface which the tragus offers to waves 

 which have been reflected forward from the concha, and which are finally 

 reflected into the meatus. It must be stated, however, that some authorities 6 

 hold that the auricle does not act as a reflector of sound at all. 



Another function of the auricle, probably quite as important as its 

 acoustic function, is its protective influence. The mouth of the meatus is 

 somewhat twisted, and since the tragus projects backwards over it, the difficulty 

 of foreign bodies obtaining entrance is much increased. The stiff hairs which 

 are present in the lower animals, and frequently also in the human subject, at 

 the entrance to the meatus, no doubt aid in this protective function, by pre- 

 venting the entrance of dust, insects, etc., into the outer canal. 



The external auditory meatus. — The functions of the external 

 auditory meatus are (1) to conduct waves of sound to the membrana 

 tympani, and (2) to afford protection to this membrane and the delicate 

 structures in the middle ear. 



As regards its first function, the question of its action upon the 

 reflection of sound again comes into consideration, and authors are 

 not wanting who find in its various curves a means of reflecting 

 the waves of sound to the drum-head. Such curves exist at two 

 places, one at the depression on the posterior wall of the cartilagin- 

 ous meatus, immediately after its commencement, and the other at 

 the concavity which occupies the anterior and inner wall of the meatus, 

 and which is subtended by the tympanic membrane. Politzer 7 states 

 that the latter concavity is in the form of a parabolic curve, and will 

 thus reflect sound-waves very powerfully on to the membrane. The 



1 London, Edinburgh, and Dublin Phil. Mag., London, 1882, vol. xiii. p. 413. 



2 When no reference is given to statements by M'Kendrick and Gray, it will be under- 

 stood that these are the result of experiments and observations made lor the purpose of this 

 article. 



3 Arch./. Ohrenh., 1874, Bd. ix. S. 72. 4 Op. tit., p. 416. 5 Op. cit., p. 55. 

 6 Kiipper, Arch. f. Ohrenh., 1873, Bd. viii. S. 158. 7 Op. cit., p. 57. 



