THE SPECIAL SKN 



103. The vestibule communicates with the chain of 

 bones of the middle ear by means of a small open ing, 

 called the "oval wfadow," or/emfaa oralis. Across this 

 window is stretched the membrane, which has already 

 been alluded to as being joined to the stirrup-bone of the 

 middle ear. Through this window, then, the sound-wave. 

 which traverses the external and middle ear, arrives at last 

 at the labyrinth. The limpid fluid which the latter con- 

 tains, and which bathes the terminal fibres of the nerve of 

 hearing, is thus agitated, the nerve-fibres are excited, and 

 a sonorous impression is conducted to the brain, or, as we 

 say, a sound is heard. 



104. Protection of the Sense of Hearing. From 

 what has been seen of the complicated parts which com- 

 pose the organ of hearing, it is evident that while many 

 of them possess an exquisite delicacy of structure, Nature 

 has well and amply provided for their protection. We 

 have observed the concealed situation of the most impor- 

 tant parts of the mechanism of the ear, the length of its 

 cavity, its partitions, the hardness of its Avails, and its 

 communication with the atmosphere; all these provisions 

 rendering unnecessary any supervision or care on our part 

 in reference to the interior of the ear. But in respect to 



. ternal parts, which are under our control and within 

 the reach of harm, it is otherwise. We may both observe 

 the dangers which threaten them, and learn the means 

 necessary to protect them. 



105. One source of danger to the hearing consists in 

 lowering the temperature of the ear, especially by the 

 introduction of cold water into the auditory canal. Every 

 one is familiar with the unpleasant sensation of distension 

 and the confusion of sounds which accompany the filling 

 of the ear with water when bathing: the weight of the 



1OS. With what doo* tin- vestibule communicate? What is the theory bv 

 \\hich sound is conducted to the brain? 



104. The formation of the onran of hearing with a view to it* protection? 



105. Danger to which tin- hearing may be "subjected ? Ae.\ 



