226 THE HUMAN BODY 



the ear each note is analyzed into its components; and that the 

 difference of sensation which we call timbre is due to the effect of 

 the secondary partial tones thus perceived. If so, the ear must 

 have in it an apparatus adapted for sympathetic resonance. 



The External Ear. The auditory organ in man consists of 

 three portions, known respectively as the external ear, the middle 

 ear or tympanic cavity, and the internal ear or labyrinth; the latter 

 contains the end organs of the auditory nerve. The external ear 

 consists of the expansion seen on the exterior of the head, called 

 the concha, M, Fig. 69, and a passage leading in from it, the ex- 



FIG. 69. Semidiagrammatic section through the right ear (Czermak). M, con- 

 cha; G, external auditory meatus; T, tympanic membrane; P, middle ear; o, oval 

 foramen; r, round foramen; R, pharyngeal opening of Eustachian tube; V, vesti- 

 bule; B, a semicircular canal; S, the cochlea; Vt, scala vestibuli; Pt, scala tympani; 

 A, auditory nerve. 



ternal auditory meatus, G. This passage is closed at its inner end 

 by the tympanic or drum membrane, T. It is lined by skin, through 

 which numerous small glands, secreting the wax of the ear, open. 

 The Functions of the Tympanic Membrane. If a stretched 

 membrane, such as a drumhead, be struck, it will be thrown into 

 periodic vibration and emit for a time a note of a determined pitch. 

 The smaller the membrane and the tighter it is stretched the higher 

 the pitch of its note; every stretched membrane thus has a rate of 

 its own at which it tends to vibrate, just as a piano or violin string 



