THE EXTERNAL EAR. 817 



ments of Wreden, to become convinced that the subjective auditory phenomena, attrib- 

 uted by Brenner and others to irritation of the auditory nerves, are due to contraction 

 of the muscles of the middle ear, particularly the stapedius. The facts, clinical and ex- 

 perimental, upon which this view is based, are the following : In cases of clonic spasm of 

 the stapedius, sensations of sound have been observed, exactly like those produced by an 

 induced current. In cases of complete facial paralysis from otitis, in which paralysis of 

 the auditory nerve could be positively excluded, it was not possible to produce subjective 

 auditory sensations, even by powerful galvanization by a catheter passed through the 

 Eustachian tube into the tympanic cavity, or by the external meatus. In addition, there 

 are other well-established clinical observations, mentioned by Wreden, which sustain the 

 theory of muscular contraction and are opposed to the idea of direct stimulation of the 

 auditory nerves. 



The facts just stated show that there is no positive evidence of the production of im- 

 pressions of sound by galvanic stimulation of the auditory nerves ; while it appears from 

 experiments, that these nerves are not endowed with general sensibility. The results, 

 then, as regards the auditory nerves,, are simply negative. Were it possible to subject 

 these nerves to mechanical or galvanic stimulation, in the human subject, without involv- 

 ing other parts, we might arrive at ome definite conclusion ; but the difficulties in the 

 way of such an experiment, it must be admitted, have thus far proved insurmountable. 



Topographical Anatomy of the Parts essential to the Appreciation of Sound. 



Perfect audition requires the anatomical integrity of a very complex apparatus, which, 

 for convenience of anatomical description, may be divided into the external, middle, and 

 internal ear. A correct appreciation of the physiology of these parts demands, as a neces- 

 sary preparation, a knowledge of their physiological anatomy : 



1. The external ear includes the pinna and the external auditory meatus, which is 

 closed internally by the membrana tympani. 



2. The middle ear includes the cavity of the tympanum, or drum, with its boundaries. 

 The parts here to be described are, the membrana tympani, the form of the tympanic 

 cavity, its openings, its lining membrane, and the small bones of the ear, or ossicles, with 

 their ligaments, muscles, and nerves. The cavity of the tympanum communicates, by 

 the Eustachian tube, with the pharynx and also, presents openings into the mastoid cells. 



3. The internal ear contains the terminal filaments of the auditory nerve. It includes 

 the vestibule, the three semicircular canals, and the cochlea, which together form the 

 labyrinth. 



The pinna and the external meatus simply conduct the waves of sound to the tym- 

 panum. The parts entering into the structure of the middle ear are accessory, and are 

 analogous in their functions to the refracting media of the eye. Structures contained 

 in the labyrinth constitute the true sensory organ ; and these bear the same relations to 

 the auditory apparatus as the retina to the eye. 



The External Ear. It is hardly necessary to our purpose to describe very minutely 

 the external ear. The pinna, or auricle is that portion projecting from the head, which 

 first receives the waves of sound. Beginning externally, we have the helix, which is the 

 outer ridge of the pinna. Just within this, is a groove, called the fossa of the helix. This 

 fossa is bounded anteriorly by a prominent but shorter ridge, called the antihelix ; and 

 above the concha, between the superior portion of the antihelix and the anterior portion 

 of the helix, is a shallow fossa, called the fossa of the antihelix. The deep fossa, imme- 

 diately surrounding the opening of the meatus, is called the concha. A small lobe pro- 

 jects posteriorly, covering the anterior portion of the concha, which is called the tragus ; 

 and the projection at the lower extremity of the antihelix is called the antitragus. The 

 fleshy, dependent portion of the pinna is called the lobule of the ear. 

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