626 THE EAE 



with the saccule and utricle by means of the canalis reiiniens, as 

 described above. 



The scala tympani and scala vestibuli, on either side of the scala 

 media, extend spirally from the base to the apex of the cochlea. At 

 the apex they are united by the Jielicotrema, a continuation of these 

 canals which curves around the hamulus. At the base of the coch- 

 lea the two canals diverge, the scala tympani ending abruptly at 

 the fenestra rotunda, which is closed by a fibrous membrane, clothed 

 on its tympanic surface by the-flattened epithelium of the tympanic 

 mucosa, and on its cochlear surface by the epithelium of the scala 

 tympani. The scala vestibuli, on the other hand, is continued 

 backward into the vestibule, where it is in relation with the exter- 

 nal surface of the saccule and utricle, and, since it is in contact 

 with the outer wall of the bony vestibule, this portion of the scala 

 vestibuli receives the opening of the fenestra ovalis, which is closed 

 by the foot plate of the stapes. Corresponding to the relative posi- 

 tions of the fenestra ovalis and fenestra rotunda, 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 por- 

 tions of the cochlea, we are now in a position to study more care- 

 fully the finer structure of its more important parts. 



The membranous wall of the scala tympani and scala vestibuli 

 is clothed by a layer of flattened endothelial 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 scalse are peri- 

 lymphatic canals. 



The membrane of Reissner is an extremely delicate structure 

 which consists of a thin central substantia propria, covered on 

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

 tinuous with the endothelium of the scala vestibuli, that on the 

 other with the endothelium of the scala media. 



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

 the endothelium in that portion which adjoins the membrane of 

 Eeissner, 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 liga- 

 mentous structure, triangular in shape as seen in a longitudinal 

 section of the cochlea, which receives the insertion of the membrana 



