Chap, viii.] 



OF THE SENSE OF HEARING, 



417 



is lined witli cyliadrical epithelial cells. Beneath are found other 

 cells sending baoilla between the epithelial cells. At this base 

 these cells emit fine filaments which seem to be in relation with 

 the nerves (Kg. 76). It is a structure very analogous to that 

 of the olfactory membrane. 



In man and the superior vertebrates the auditory organ is 

 composed, as is well known, of three 

 parts, namely : — the external ear, 

 comprehending the pavilion of 

 the ear and the external auditory 

 conduit, shut by the membrane of 

 the tympanum : the mediali ear, 

 composed of the cavity of the 

 tympanum, communicating with 

 the throat through the Eustachian 

 tube and traversed by the chain 

 oi the ossicles ; finally, the internal 

 ear, constituted schematically by 

 an ampulla full of liquid, and 

 containing otoliths. It is also 

 known that this internal ear is 

 subdivided into vesdbtile, semi- 

 circular canals, and into a part 

 rolled spiKilly, the cochlea. The 

 fundamental portion of all this 

 complicated apparatus is evidently 

 the internal ear, in which are 

 formed the terminal threads of the 



Fia. 76. 

 Microscopical preparation talcen from the 

 partition of th« auditory ampulla of the 

 clavated ray (^aja clavata): a, cylindri- 

 cal nucleaiiod cell, fonuiug the internal 

 epithelium ; 6, nucleates cells terminat 

 ing in line fllaments and resting on the 

 cartilage travened hy the nervous 

 fihres, /, which terminate in very fine 

 Tamiiications, g ; the ramifications con- 

 tinue veryprohahly in the fine ^laments, 

 e, with which commence the nucleated 

 cells, c, of which the terminations in 

 auditory bacilla, d, are placed between 

 the cells, a, of the epithelium. 



.auditory nerve. The other parts 

 are accessory, and are more or less lacking in many vertebrates. 

 The internal ear is simplified more and more in proportion as we 

 descend in the series. The aquatic mammifers and birds have 

 no external ears. The median ear gradually disappears in reptiles 

 and the amphibia. Already in the inferior vertebrates the cochlea 

 its usual shape. Instead of the spiral cochlea birds 



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