CHAP, viii.] 



OF THE SENSE OF HEARING. 



417 



is lined with cylindrical epithelial cells. Beneath are found other 

 , cells sending bacilla between the epithelial cells. At this base 

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

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

 of the olfactory membrane. 



In man and the superior vertebrates the auditory or<*nn 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 median ear, 

 composed of the cavity of the 

 tvmpanum, communicating with 

 the throat through the Eustachian 

 tube and traversed by the chain 

 of 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 Fio _ 6 



subdivided into vestibule. semi- Microscopical preparation taken from the 



partition of the auditory ampulla of the 



Circular Canals, and into a part clavated ray rJJaja elamta): a, cylindii- 



cal nucleated cell, forming- the internal 

 epithelium ; 6, nucleated cells terminal 

 ing in fine filaments and resting on the 

 cartilage traversed by the nervous 

 fibres, /, which terminate in very fine 

 ramifications, g; the ramifications con- 

 tinue very probably in the fine filaments, 

 e, with which commence the nucleated 

 cells c, of which the terminations in 

 auditory bacilla, d, are placed between 

 'the cells, o, of the epithelium. 



rolled spirally, the cochlea. The 



fundamental portion of all this 



complicated apparatus is evidently 



the internal ear, in which are 



formed the terminal threads of the 



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 



loses its usual shape. Instead of the spiral cochlea birds 



E E 



