SENSE OF HEARING. 



613 



to the outer bony wall of the cochlea, where it is enlarged, forming 

 the ligamentum spirale. From the base of the labium vestibulare 

 a membrane (Reissner's membrane) extends to the outer wall, above 

 and nearly parallel with the membrana basilaris. Between this 

 membrane and the membrana basilaris is the ductus cochlearis or 

 ductus auditoriuSj and in this, situated upon the membrana basilaris, 



FIG. 393. Section through one of the turns of the osseous and membranous 

 cochlear ducts of the cochlea of a guinea-pig : Z, scala vestibuli ; m, labium vestibu- 

 lare of the limbus ; n, sulcus spiralis internus ; o, nerve-fibers lying in the lamina 

 spiralis ; p, ganglion -cells ; q, blood-vessels ; a, bone ; 6, Eeissner's membrane ; DC, 

 ductus cochlearis; d, Corti's membrane; /, prominentia spiralis; g, organ of Corti: 

 h, ligamentum spirale; i, crista basilaris; k, scala tympani ; X 90 (Bohm and 

 Davidoff). 



is the organ of Corti. The membrana basilaris is composed of stiff, 

 straight fibers, estimated at 24,000 in number, which are embedded 

 in a homogeneous stratum. It is much broader in the uppermost 

 tarns of the cochlea than in the lowest ; the width being at the 

 bottom, 0.21 mm. ; in the middle, 0.34 mm. ; and at the top, 

 0.36 mm." 



