AUDITORY ORGANS. 



433 



Considering for the moment that a transverse section of the cochlear 

 canal only one cell deep is being dealt with, the organ of Corti will be 

 found to consist of a central part composed of two peculiarly shaped rods 



- u 



FIG. 30.3. DIAGRAMS OF THE MEMBRANOUS LABYRINTH. (From Gegenbaur. ) 

 I. Fish. II. Bird. III. Mammal. 



I', ufcriculus ; S'. sacculus ; VS. utriculus and sacculus; Cr canalis reuniens ; 

 11. recessus labyrinth! ; f'C. commencement of cochlea; C. cochlear canal ; L. lagena; 

 K. cupola at apex of cochlear canal ; I", ciecal sack of the vestibulum of the cochlear 



canal. 



widely separated below, but in contact above. These are the rods or 

 fibres of Corti. On their outer side, i.e. on the side towards the 

 osseous wall of the canal, is a reticulate membrane which passes from the 

 inner rod of Corti towards the osseous wall of the canal. With their 

 upper extremities fixed in that membrane, and their lower resting on the 

 basilar membrane are three (four in man) cells with auditory hairs known 

 as the outer 'hair cells,' which alternate with tlrree other cells known 

 as Deiters' cells. Between these and the outer attachment of the basilar 

 membrane is a series of cells gradually diminishing in height in passing- 

 outwards. On the inner side of the rods of Corti is one hair cell, and 

 then a number of peculiarly modified cells which till up the space between 

 the two lips of the lamina spiralis. 



It will not be necessary to say much in reference to the development 

 of the labium tympanicum and the labium vestilmlare. 



The labium vestibulare is formed by a growth of the connective tissue 



tJ O 



which fuses with and passes up between the epithelial cells. The epithelial 

 cells which line its upper (vestibular) border become modified, and remain 

 as its teeth. 



The labium tympanicum is formed by the coalescence of the connective 

 tissue layer separating the scala tympani from the cochlear canal with part 

 of the connective tissue of the lamina spiralis. At first these two layers 

 are separate, and the nerve fibres to the organ ot Corti pass between 

 them. Subsequently however they coalesce, and the region where they are 

 penetrated by the nervous fibres becomes the habcnula perforata. 



B.E. II. 28 



