SENSE OF HEARING USES OF LABYRINTH. 



791 



enabled to estimate the pitch of sounds, particularly of the voice ; and he 

 adduces, in support of this idea, the fact, that the development of the cochlea 

 follows a very similar proportion with the compass of the voice. This is 

 much the greatest in the Mammalia; less in Birds; and in Reptiles which 

 have little true vocal power, the cochlea is reduced to its lowest form, dis- 

 appearing entirely in the Amphibia. That there should be an acoustic rela- 

 tion between the voice and ear of each species of animal, cannot be re- 



Vertical Section of the Human Ear, the internal portions on an enlarged scale : a, 6, c, external ear; 

 d, entrance to auditory canal,/; e, e, petrous portion of temporal bone; g, membrana tympani; h, 

 cavity of the tympanum, the chain of bones being removed; i, openings from this cavity into the 

 cells, _/, excavated in the bone ; on the side opposite the membrana tympani are seen the fenestra 

 ovalis and rotunda; k, Eustachian tube; I, vestibule ; m, semicircular canals ; n, cochlea ; o, auditory 

 nerve ; p, canal for carotid artery ; q, part of glenoid fossa ; r, styloid process ; s, mastoid process. 



garded as improbable ; and the speculation of M. Duges derives confirmation 

 from the researches of Helmholtz, who appears to consider that the function 

 of the cochlea stands in intimate relation with our power of discriminating 

 differences in the quality of sounds. This will naturally follow from his 

 demonstration that the timbre depends upon the harmonic combinations ; if 

 it be the function of the cochlea to discriminate pitch. According to his 

 observations, the individual branches of the auditory nerve are only capable 

 of distinguishing simple, pendulum-like vibrations; but, as already stated 

 ( 640), all ordinary sounds are compound in their nature, the fundamental 

 note being accompanied by harmonics ; these throw corresponding fibres into 

 vibration, and produce an impression which may be likened to a color. The 

 analogy which exists between the power of distinguishing colors and that of 

 discriminating musical tones has long been recognized ; and whilst we find 

 that some persons are endowed w r ith the latter, which is commonly known as 

 a " musical ear," in a degree that renders it a source of great discomfort to 

 them (since every discordant sound is a positive torment), others are alto- 

 gether destitute of it, the deficiency being very analogous to the " color- 



