Chap. 40.] [ 375 ] 



CHAP. XL. 



HEARING, AND ITS ORGANS. 



Defcription of the Ear. Admirable Structure of this Organ for con- 

 veying and echoing Sound. -Ears of different Animah. Manner in 

 which the Puljes of Air are conveyed to the Ear.- Communication 

 by the Euftachian Tube. Reafon <wby Perfons who lijlen attentively 

 'open their Mouths. The Membrana Ijmpani probably the great In- 

 Jlrument of hearing. 



AS by the fenfe of fmelling we diftinguifli certain 

 particles floating in the' air, fo by that of hear- 

 ing we difcover the motions and vibrations of the air 

 itfelf. The parts of the ear are diftinguiihed into 

 external and internal. The former of thefe divifions 

 comprehends all thofe parts which we are able to ob- 

 ferve without direction, and which are feparated from 

 thofe of. the internal ear by the membrana tympani, 

 improperly called the drum of the ear, as it is only a 

 membrane flretched before the entrance of the cavity 

 which is properly the ear. The external ear, which 

 from its refemblance to a certain fea (hell is called 

 concha, is a cartilaginous funnel of an irregular oval 

 form, moveably connected to the head by ligaments, 

 mufcles, and cellular fubftance. The mufcles with 

 which the ear is furnimed, and which are much 

 employed by quadrupeds, are of little or no ufe to 

 man. 



Different parts of the external ear are known by 

 different names ; its upper cartilaginous part is called 

 the ala or wing, to diftinguim it from the fofc 

 and pendent part below, called the lobe ; its outer 

 border or circle is called the helix, and the femicircle 

 B b 4 within 



