i88 



Human Physiology. 



As the sound waves move with a velocity of about a mile in 

 four seconds we see the flash of a gun before we hear the re- 

 port, and can judge of the distance of lightning by noting the 

 time it takes for the thunder to reach us. A long column of 

 soldiers cannot all keep step at once to the music ; and singers 

 or players of instruments, far apart, cannot keep together. 



The waves of sound, larger or smaller as the sounds are grave 

 or acute, enter the opening of the ear. The long ears of the ass, 

 horse, rabbit, &c., seem to be useful in gathering and concen- 

 trating these vibrations, but the external ear of man is probably 

 more ornamental than useful ; and birds and many animals 

 have very acute hearing without any external ear whatever. 

 About an inch within the human ear is placed a membrane, 

 like the head of a drum, which receives the vibrations of sound. 

 Within this tympanum is an air chamber connected by a tube, 

 the eustachian, with the mouth, and three small bones, joined 

 to each other, aid in carrying the atmospheric impulses to the 

 labyrinth or internal ear, which is the real organ of hearing, 

 where the auditory nerve fills three semicircular canals and a 

 very curiously formed cochlea, or shell-like spiral chamber 



(Fig. 35), where its fibres 

 may be seen spread out 

 and gradually shortening 

 like the strings of a harp 

 or pianoforte, as if each 

 sound from lowest pitch 

 to highest had a separate 

 nerve fibre to convey it 

 to the sensorium ; where 

 atmospheric vibrations are 

 finally converted into all 

 the wondrous modulations 

 of music and speech. This 

 true ear, the organ of hearing, is embedded in the bones of the 



Fig 35. LABYRINTH OF THE EAR, LAID 

 OPEN, MAGNIKIKD. 



