606 



THE NERVOUS SYSTEM. 



ear, and is closed by the stapes, an annular ligament uniting the 

 bone to the fenestra. 



Fenestra Eotunda. This opening, also on the internal wall of 

 the tympanum, leads into the cochlea of the internal ear. It is 



FIG. 386. Eight bony labyrinth, viewed from outer side: the figure represents 

 the appearance produced by removing the petrous bone down to the denser layer 

 immediately surrounding the labyrinth : 1, 2, 3, the superior, posterior, and external 

 or horizontal semicircular canals ; 4, 5, 6, the ampullse of the same ; 7, the vestibule ; 

 8, the fenestra ovalis ; 9, fenestra rotunda ; 10, first turn of the cochlea ; 11, second 

 turn ; 12, apex (from Quain., after Sommerring). 



FIG. 387. Interior view of left bony labyrinth after removal of the superior and 

 external walls : 1, 2, 3, the superior, posterior, and external or horizontal semicir- 

 cular canals ; 4, fovea hemi-elliptica ; 5, fovea hemispherica ; 6, common opening of 

 the superior and posterior semicircular canals ; 7, opening of the aqueduct of the 

 vestibule ; 8, opening of the aqueduct of the cochlea ; 9, the scala vestibuli ; 10, 

 scala tympani ; the lamina spiralis separating 9 and 10 (from Quain, after Som- 

 merring). 



closed by the membrana tympani secundaria, which is made up of 

 an external or mucous layer, a continuation of that lining the 

 tympanum ; and an internal or serous, a continuation of that lining 

 the cochlea ; between these two is a third or fibrous layer. Be- 



