THE EXTERNAL EAR 



713 



subject the nerves to mechanical or electric stimulation in the human 

 subject without involving other parts, it might be possible 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 

 apparatus, 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 mem- 

 brana 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. Fig. 183. The pinna (Sappey). 



3. The internal ear contains the terminal i, i, helix; 2, 2, fossa of the 



i r ,1 j-, T^. i j helix; 3, 3, antihelix; 4, fossa of 



filaments of the auditory nerve. It includes the ant iheiix; 5, concha; 6, tra- 

 the vestibule, the three semicircular canals and s us ; 7, antitragus; 8, external 



. r 111-1 auditory meatus; 9, lobule. 



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 refract- 

 ing media of the eye. Structures contained in the labyrinth constitute 

 the true sensory organ. 



The External -Ear. The pinna, auricle, or pavilion 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, bifurcating above and anteriorly, called 

 the antihelix ; and above the concha, between the bifurcating arms of 

 the antihelix and the anterior portion of the helix, is a shallow fossa, 

 called the fossa of the antihelix. The deep fossa immediately sur- 



