730 SPECIAL SENSES. 



ologists have thought that auditory sensations were produced ; but it is proba- 

 ble that the sensations observed were due to clonic spasm of the stapedius 

 muscle and not to impressions of sound produced by the action of the stimu- 

 lus upon the auditory nerves. In cases of complete facial paralysis from 

 otitis, in which paralysis of the auditory nerve could be positively excluded, 

 it has not been possible to produce subjective auditory sensations, even by 

 powerful Faradization by means of a catheter passed through the Eustachian 

 tube into the tympanic cavity or by the external meatus (Wreden). In addi- 

 tion there are well established clinical observations which sustain the theory 

 of muscular contraction and are opposed to the idea of impressions of sound 

 produced by direct stimulation of the auditory nerves. The results, then, 

 as regards stimulation of the auditory nerves, have been simply negative. 

 Were it practicable to subject the nerves to mechanical or electric stimula- 

 tion, in the human subject, without involving other parts, it might be pos- 

 sible to arrive at a definite conclusion ; but the difficulties in the way of 

 such an experiment have thus far proved insurmountable. 



TOPOGRAPHICAL ANATOMY OF THE PARTS ESSENTIAL TO THE APPRE- 

 CIATION OF SOUND. 



"Perfect audition involves the anatomical integrity of a complex appa- 

 ratus, which, for convenience of anatomical description, may be divided into 

 the external, middle and internal ear. 



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

 and is bounded 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 it 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 tympanum. The parts entering into the structure of the middle ear 

 are accessory, and are analogous in their uses to the refracting media of the 

 eye. Structures contained in the labyrinth constitute the true sensory organ. 



The External Ear. The pinna, or auricle, is that portion projecting from 

 the head, which first receives the waves of sound. The outer ridge of the 

 pinna is called the helix. 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, immediately surrounding the 

 opening of the meatus, is called the concha. A small lobe projects pos- 

 teriorly, covering the anterior portion of the concha, which is called the 



