Hearing, and the Ear. 471 



of this point, the forward end next the mouth becomes the eustachian 

 tube, while the rear end, next the tympanic membrane, is the tympanic 

 cavity or drum. The hammer and anvil bones are developed from the 

 firsl gill arch, the stapes ( stirrup ) from the second. ( Haeckel. ) 



The division of the musical scale into seven intervals appears to have 

 been purely accidental, and has been transmitted with its variations and 

 growth from the ancients. Our adherence to the present scale, and 

 especially the readiness with which children take to it, shows the nature 

 of an instinct to be hereditary acquirement, for it is not founded in any 

 natural necessity but in a chance habit. ( See History of the Scale in 

 Blaserna's Theory of Sound. ) Octaves are natural chords it is true, 

 but they are chords in a 

 geometrical ratio, while 

 equally true chords go 

 by arithmetical ratios, 

 and would be at least as 

 natural. Vocalization 

 depends on the auditory 

 sense. People who 

 are born deaf are also 



FIG. 216. Ear bones of Mon- 

 keys compared with those 

 of Man. 



A. Lemur. 



B. Cebus. 



C. Cercopithecus. 



S. Man. 

 bserye the progressive evo- 

 lution of the " process "/ 



dumb, unless carefully 

 trained, although their 

 vocal organs may be all 

 right. In like manner 

 the perfection of musi- 

 cal accomplishments de- FlG 2 ie. 



pends on the quality of the ear. A great many birds not only have one 

 or more songs of their own, but are able to learn the songs of others, 

 so that they must be reckoned to possess a discrimination of sounds, 

 and that without the organs of corti, as stated above. It is probable 

 that the function of pitch may be connected with the cross fibres of the 

 basilar membrane (fig. 197), their progressively increasing length from 

 bottom to top corresponding with a descending musical scale. A num- 

 ber of other animals besides birds and men possess musical talents. An 

 ape of the Gibbon family produces an exact octave of musical sounds, 

 ascending and descending the scale by half tones. A good many of the 



