THE EAR. 



By John Gray M'Kendrick and Albert A. Gray. 



Contents : — The External Ear, p. 1149 — The Auricle, p. 1149 — The External Audi- 

 tory Meatus, p. 1150 — Movements of the Auricle, p. 1152 — The Middle Ear, p. 

 1152— The Tension of the Membrana Tympani, and its Regulation, p. 1152 — 

 Movements of the Membrana Tympani in response to Sound Pressures, p. 1153 — 

 The Movements of the Malleus, p. 1155 — The Movements of the Incus, p. 1155 

 — The Movements of the Stapes, p. 1156 — The Tensor Tympani, p. 1156— The 

 Stapedius, p. 1157 — The Movements of the Ossicles as a whole under the Influence 

 of Sound-waves, p. 1158 — The Magnitude of the Movements of the Ossicles, p. 

 1159 — Transmission of Sound to the Labyrinth otherwise than by the Ossicles, 

 p. 1160 — Regulation of Atmospheric Pressure in the Tympanum, p. 1161 — 

 Auditory Reflexes, p. 1162 — Binaural Audition, p. 1163 — The Internal Ear, p. 

 1164 — General Mechanism of Internal Ear, p. 1164 — The Utricle and Saccule, p. 

 1166— The Cochlea, p. 1168— Pitch, p. 1169— Beats, p. 1169— Beat Tones, p. 1170 

 — Audibility as affected by Intensity, p. 1171 — The Analytic Properties of the 

 Ear, p. 1171 — Resonance, p. 1177 — Probable Action of the Cochlea, p. 1179 — 

 Upper Partial Tones and the Theory of Dissonance, p. 1186 — Combination Tones, 

 p. 1188 — Objections to the Theory of Helmholtz, p. 1190 — Other Theories, p. 

 1190— The Semicircular Canals, p. 1194. 



The External Ear. 



The auricle. — The most natural supposition is that the auricle reflects 

 sound-waves into the external meatus. But cases of absence of the 

 auricle have been recorded without any appreciable diminution in the 

 power of hearing, 1 and persons from whom the external ear has been 

 removed have been found to possess normal hearing power. Experi- 

 ments upon the auricle, in which the depressions on its surface were 

 filled up, have given contradictory results. 2 M'Kendrick 3 found that 

 covering the external ear with plaster of Paris, leaving the entrance to 

 the canal free, weakened the intensity, and altered the quality of tones. 

 It must be observed that in such experiments the mass of the auricle 

 itself would not be able to vibrate to the same extent as in the normal 

 condition, and hence an apparent diminution of hearing may have been 

 due to a loss of vibrations conducted by the solid structures, and not to 

 the loss of the reflecting action of the auricle. 



Long ago, Boerhaave attempted to show mathematically that the concha 

 acts as a parabolic reflector, collecting and throwing vibrations into the 

 meatus. Savart, 4 however, demonstrated experimentally that this is not the 

 case. Still there is evidence that the concha does in a slight degree affect 

 acuteness of hearing by reflection. Thus 5 if a small tube, curved like a 



1 Allen Thomson, London and Edinburgh Month. Journ. Med. Sc, April 1S47 ; Toynbce, 

 "Diseases of the Ear," London, 1868, p. 14. 



2 Schneider, " Inang. Diss.," Marburg, 1855; Harless, Wagner's " Handworterbuch d. 

 Fhysiol.," 1853, Bd. iv. S. 422. 



3 "Text-Book of Physiology," vol. ii. p. (372. 



4 Journ. de physiol. cxpir., Paris, 1824, tome iv. p. 183. 



5 Politzer, "Diseases of the Ear," 1894, p. 710. 



