CHAPTER XII. 



Sense oj hearing. Organ of hearing. External ear; pavilion of the 

 ear, auditory canal. Middle ear; tympanum, drum, or membrana 

 tympani, fenestra ovalis, fenestra rotunda, Enstachian tube, the small 

 bones of the ear, muscles and movements of the small bones. Internal 

 ear; labyrinth, vestibule, semicircular canals, cochlea, membranous 

 labyrinth. Auditory nerve. Noises and sounds; duration, pitch, in- 

 tensity and quality of sound; passage of sound through air, water, solid 

 bodies; gravity, sharpness of sound. Mechanism of hearing ; functions 

 of different parts of the ear; movement of sounds in the ear; propagation 

 of sounds to the audilory apparatus by the vibrations of the bones of the 

 skull. Opinions of physiologists on the functions of different portions of 

 the labyrinth; theory of llelmholtz. Fineness and delicacy of hearing. 

 Correctness of the ear. Estimation of the intensity, the distance, and 

 the direction of sounds; ventriloquism. Duration of auditory impres- 

 sions. Sensations having an internal origin. Parallel between the 

 eye and ear. 



The ear. The organ of hearing is not placed on the face, 

 like those of sight, smell, and taste; but in the thickness of 

 the base of the skull. But we may say it belongs to the face 

 as one of the elements of the physiognomy, by its external 

 apparatus, which contributes to the expression of the head. 

 The ear is divided anatomically into three regions the exter- 

 nal, middle, and internal ear. 



External ear. This is the least complicated portion of the 

 organ; it is composed of the pavilion, or projecting part, and 

 the auditory canal. 



T}\e pavilion of the ear is similar, as the name implies, to 

 the open portion of wind-instruments or a speaking-trumpet. 

 It is an acoustic horn, which gathers the sonorous waves, and 

 conducts them to the intricacies of the auditory apparatus. 

 It consists of an elastic cartilaginous layer covered with a 



