SENSE OF HEARING. 543 



upon the organ, than upon any change in the organ itself. This habit 

 may be cultivated in regard to sounds of some one particular class ; all 

 others being heard as by an ordinary person. Thus, the watchful 

 North American Indian recognises footsteps, and can even distinguish 



Fig. 161. 



A diagram of the Ear : p. The pina. t. The tympanum. 1. The labyrinth. 1. The upper part of the 

 helix. 2. The antihelix. 3. The tragus. 4. The antitragus. 5. The lobulus. 6. The concha. 7. The upper 

 part of the fossa scaphoidea. 8. The meatus. 9. The membrana tympani, divided by the section. 10. The 

 three little bones, crossing the area of the tympanum, malleus, incus, and stapes ; the foot of the stapes 

 blocks up the fenestra ovalis upon the inner wall of the tympanum. 11. The promontory. 12. The fenestra 

 rotunda; the dark opening above the ossicula leads into the mastoid cells. 13. The Eustachian tube; the 

 little canal upon this tube contains the tensor tympani muscle in its passage to the tympanum. 14. The 

 vestibule. 15. The three semicircular canals, horizontal, perpendicular, and oblique. 16. The ampullae 

 upon the perpendicular and horizontal canals. 17. The cochlea. 18. A depression between the convexities 

 of the two tubuli which communicate with the tympanum and vestibule ; the one is the scala tympani, 

 terminating at 12; the other is the scala vestibuli. 



between the tread of friends and foes ; whilst his white companion, 

 who has lived among the busy hum of cities, is unconscious of the 

 slightest sound. Yet the latter may be a musician, capable of dis- 

 tinguishing the tones of all the different instruments in a large orches- 

 tra, of following any one of them through the part which it performs, 

 and of detecting the least discord in the blended effects of the whole, 

 effects which would be to the unsophisticated Indian but an indistinct 

 mass of sound. In the same manner, a person who has lived much in 

 the country, is able to distinguish the note of every species of bird 

 that lends its voice to the general chorus of nature ; whilst the inhabi- 

 tant of a town hears only a confused assemblage of shrill sounds, 

 which may impart to him a disagreeable rather than a pleasurable sen- 

 sation. 



954. In all continued sounds or tones, there are several points to be 

 attended to. In the first place, we take cognizance of their pitch; 

 which depends upon the number of vibrations in a given time, the 

 high notes being produced by the most rapid vibrations, and the low 

 notes by the slowest. The ear can appreciate tones produced by 24,000 



