AUDITORY ORGANS. 



525 



epithelium of the cochlear canal a very remarkable organ known as the organ 

 of Corti, the development of which is of sufficient importance to merit a 

 brief description. A short account of this organ in the adult state may 

 facilitate the understanding of its development. 



The cochlear canal is bounded by three walls, the outer one being the 

 osseous wall of the cochlea. The membrane of Reissner bounds it towards 



U 



FIG. 305. DIAGRAMS OF THE MEMBRANOUS LABYRINTH. (From Gegenbaur.) 



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



U. utriculus ; S. sacculus ; US. utriculus and sacculus ; Cr. canalis reuniens ; 

 R. recessus labyrinthi ; UC. commencement of cochlea ; C. cochlear canal ; L. lagena ; 

 PC. cupola at apex of cochlear canal; V. csecal sack of the vestibulum of the cochlear 

 canal. 



the scala vestibuli, and the basilar membrane towards the scala tympani. 

 This membrane stretches from the margin of the lamina spiralis to the 

 ligamentum spirale ; the latter being merely an expanded portion of the 

 connective tissue lining the osseous cochlea. 



The lamina spiralis is produced into two lips, called respectively the 

 labium tympanicum and labium vestibulare ; it is to the former and 

 longer of these that the basilar membrane is attached. At the margin of the 

 junction of the labium tympanicum with the basilar membrane the former is 

 perforated for the passage of the nervous fibres, and this region is called the 

 habenula perforata. 



The labium vestibulare, so called from its position, is shorter than the 

 labium tympanicum and is raised above into numerous blunt teeth. Partly 

 springing out from the labium vestibulare, and passing from near the inner 

 attachment of the membrane of Reissner towards the outer wall of the 

 cochlea, is an elastic membrane, the membrana tectoria. Resting on the 

 basilar membrane is the organ of Corti. 



Considering for the moment that a transverse section of the cochlear 



