SENSE OF HEARING. 261 



Fig. 56. 



The labyrinth of the Left Ear, laid open in order to show its cavities and the Membranous Labyrinth ; 

 after Breschet; 1, the cavity of the vestibule, opened from its anterior aspect in order to show the three-cor- 

 nered form of its interior, and the membranous labyrinth which it contains; the figure rests upon the com- 

 mon saccule of the membranous labyrinth the sacculus communis ; 2, the ampulla of the superior or per- 

 pendicular semicircular canal, receiving a nervous fasciculus from the superior bronch of the vestibular 

 nerve; 3, 4, the superior or perpendicular canal with its contained membranous canal; 5, the ampulla of 

 the inferior or horizontal semicircular canal, receiving a nervous fasciculus from the superior branch of 

 the vestibular nerve; 6, the termination of the membranous canal of the horizontal semicircular canal in 

 the sacculus communis; 7. the ampulla of the middle or oblique semicircular canal, receiving a nervous 

 fasciculus from the inferior branch of the vestibular nerve; 8, the oblique semicircular canal with its 

 membranous canal; 9, the common canal, resulting from the union of the perpendicular with the oblique 

 semicircular canal; 10, the membranous common canal terminating in the sacculus communis; 11, the 

 otoconite of the sacculus communis seen through the membranous parietes of that sac ; a nervous fasci- 

 culus from the inferior branch of the vestibular nerve is seen to be distributed to the sacculus communis 

 near to the otoconite; the extremity of the sacculus above the otoconite is lodged in the superior ventricle 

 of the vestibule, and that below it in the inferior ventricle ; 12, the sacculus proprius situated in the ante- 

 rior ventricle; its otoconite is seen through its membranous parietes, and a nervous fasciculus derived 

 from the middle branch of the vestibular nerve, is distributed to it; the spaces around the membranous 

 labyrinth are occupied by the aqua labyrinth!; 13, the first turn of the cochlea; the figure is situated in the 

 scala tympani; 14, the extremity of the scala tympani corresponding with the fenestra rotunda; 15, the 

 lamina spiralis; the figure is situated in the scala vestibuli ; 16, the opening of the scala vestibuli into the 

 vestibule; 17, the second turn of the cochlea; the figure is placed upon the lamina spiralis, and, therefore, 

 in the scala vestibuli, the scala tympani being beneath the lamina; 18, the remaining half turn of the 

 cochlea; the figure is placed in the scala tympaui; 19, the lamina spiralis terminating in a falciform ex- 

 tremity ; the dark space included within the falciform curve of the extremity of the lamina spiralis is the 

 helicotrema ; 20, the infundibulum. 



parts may be thrown into reciprocal vibration, even though the tone of the 

 whole be different, or it be not capable of producing a definite tone at all. 

 This is the case, for example, when a tuning-fork in vibration is placed upon 

 a sound-board ; for even though the whole board have no definite fundamental 

 note,* it^tt divide itself into a number of parts, which will reciprocate the 



* The fundamental note of & body is the lowest tone which it will yield, when the whole 

 of it is in vibraftj^ together. By dividing the body into two or more distinct parts, it 

 may be made to^pre a great variety of sounds. Thus, if a stretched string be divided 

 by a bridge into two equal parts, each will sound the octave of the fundamental note, or 

 the 8th note above it. If it be divided into three parts, each will give the 12th above the fun- 

 damental note ; if into four, the 15th or double octave will be heard ; if into five, the 17th ; 

 if into six, the 19th; if into seven, the 20 (flat seventh above the second octave); if into 

 eight, the 22dor triple octave. A string forcibly set in vibration has a tendency to sound 

 these harmonics with the fundamental note, by spontaneous division into several distinct 

 segments of vibration ; as may be easily made evident, by striking one of the lower keys 

 of the piano, and listening to the sounds heard whilst the fundamental note is dying away. 



