704 THE EAE 



since it is in contact with the outer wall of the bony vestibule, this por- 

 tion of the scala vestibuli receives the opening of the fenestra vestibuli, 

 which is closed by the foot plate of the stapes. Corresponding to the 

 relative positions of the fenestra vestibuli and fenestra cochleae, the scala 

 vestibuli in the first turn of the cochlea lies above the scala tympani, 

 and being somewhat the longer it also extends farther backward. 



Having traced the general form and relations of the several portions 

 of the cochlea, we are now in a position to study more carefully the 

 finer structure of its more important parts. 



The membranous wall of the scala tympani and scala vestibuli is 

 alothed by a mesenchymal epithelium of flattened endothelioid cells, 

 which rest upon a double layer of fibrous tissue. Thus the tunica propria 

 also serves as a periosteum for the inner surface of the bony wall of the 

 cochlea, and conveys the blood and lymphatic vessels. The scalae are 

 perilymphatic canals. They communicate with the subdural space 

 through the aqueductus vestibuli and the aqueductus cochleae. The latter 

 opens from the scala tympani near its beginning at the fenestra coch- 

 leae, and passes below the pyramid to the dura transmitting a small 

 vein. 



The vestibular membrane (of Reissner) is an extremely delicate 

 structure which consists of a thin central substantia propria, covered 

 on either surface by epithelium, that on the one surface being con- 

 tinuous with the mesenchymal epithelium of the scala vestibuli, that 

 on the other with the ectodermal epithelium of the scala media. It is 

 non-vascular in the adult. 



The outer wall of the scala media is lined by a continuation of the 

 epithelium in that portion which adjoins the membrane of Beissner, 

 and this rests upon a fibrous membrane similar to that which forms 

 the walls of the other scalae. Toward the attachment of the membrana 

 basilaris, however, the tissue of the outer fibrous wall of the scala media 

 is much thickened, and forms a dense ligamentous structure, triangular 

 in shape as seen in a longitudinal section of the cochlea, which receives 

 the insertion of the membrana basilaris at its apex, and being, like 

 the basilar membrane, continued from the base to the apex of the cochlea, 

 is known as the spiral ligament. Its dense fibrous bands radiate from 

 the attachment of the basilar membrane to all portions of the ligament, 

 and are firmly attached to the bony wall of the cochlea, with whose 

 periosteum the deeper fibers of the spiral ligament are blended. 



The surface of the spiral ligament, which forms the outer wall of 

 the scala media, slopes gradually away from the attachment of the basilar 



