PHYSIOLOGY OF THE EXTERNAL EAR. 189 



quality may be dependent as well upon the nature of the sonorous body, 

 as upon the greater or less number of harmonics, that accompany the 

 fundamental sound. 1 



3. PHYSIOLOGY OF AUDITION. 



In tracing the progress of sonorous vibrations to the internal ear, 

 we shall follow the order of parts described in the anatomical sketch of 

 the auditory apparatus ; commencing with the external ear. The 

 meatus auditorius externus being always open, sonorous vibrations can 

 readily reach the membrana tympani. Some of these pass directly to 

 the membrane without experiencing reflection, and communicate their 

 oscillations to it. The pavilion has been regarded, by most physio- 

 logists, as a kind of ear-trumpet, for collecting aerial undulations, and 

 directing them, after various reflections, to the bottom of the auditory 

 canal. In the horse, and in those animals which have the power of 

 pricking the ears, or of moving them in various directions, this is 

 doubtless the case; but in man we cannot expect any great effect of 

 the kind, if we regard its arrangement, and the incapability of moving 

 it from its fixed direction, which is nearly parallel to the head. Boer- 

 haave, 2 indeed, pretended to have proved by calculation, that every 

 sonorous ray, which falls upon the pavilion, is ultimately directed to- 

 wards the meatus auditorius externus. Simple inspection of the pavil- 

 ion shows that this cannot be universally true. Some part of the an- 

 thelix is, in almost every individual, more prominent than the helix; 

 and it is therefore impossible for the undulations, that fall upon the 

 posterior surface of the former, to be reflected towards the concha. 

 M. Itard, 3 a distinguished physiologist and aurist of Paris, asserts, that 

 he has never seen the loss of the pavilion affect the hearing; and many 

 animals, whose sense of hearing is acute, the mole and birds, for 

 example, are devoid of it. Hence he concludes, that it is, perhaps, 

 rather injurious than favourable to audition; and is more inservient to 

 the expression than to the hearing of the animal. 



M. Itard's view is doubtless too exclusive. The pavilion may have 

 but little agency as an ear-trumpet, but it must have some. The 

 concha, being the expanded extremity of the meatus auditorius, must 

 receive more sonorous vibrations than could be admitted by the meatus 

 itself. These are reflected towards the membrana tympani, and reach 

 it in a state of concentration but, to no great amount, it is true. In 

 this way, and perhaps in that suggested by M. Savart, 4 the pavilion is 

 useful in audition. That gentleman is of opinion, that the whole of 

 the external ear, the elasticity of which he considers to be capable of 

 slight modification by the action of its proper muscles, is an apparatus 

 for repeating sonorous vibrations, and transmitting or conducting them 

 along its own parietes to the membrane of the tympanum. According 

 to this view, the different inequalities of surface of the pavilion admit 



1 On sonorous undulations in general, see Muller's Elements of Physiology, by Baly, Pt. v. 

 p. 1215, Lond., 1839. 



2 Praelect., torn. iv. p. 317. 



Traite des Maladies de 1'Oreille et de 1'Andition, i. 131, Paris, 1821. 



* Annales de Chimie, xxvi. 5; and Journal de Physiologie, iv. 183, and v. 367. 



