THE EAR 289 



into the median part of the labyrinth, the vestibule, which 

 is separated from the middle ear by the fenestra ovalis. 

 The other passage of the cochlea, the scala tympani, ends, 

 at the base, in the fenestra rotundis (compare Figs. 40 and 



In the labyrinth, therefore, the passage from the fenestra 

 ovalis to the fenestra rotundis goes through the canals of the 

 cochlea. By the vibrations of the membranes of the fenestra 

 ovalis the water in the labyrinth is caused to vibrate and 

 presumably that in the cochlea, because the passage from the 

 fenestra ovalis to the other yielding place of the labyrinth 



FIG. 40. CROSS-SECTION OF THE COCHLEA. 



wall (the membrane of the fenestra rotundis) passes through 

 the cochlea. The movement of the water in the labyrinth 

 is rendered possible by the existence of this second flexible 

 part [membrane of the fenestra rotundis]. The partition in 

 the canal of the cochlea is partly membranous, and the 

 vibrations of the water of the labyrinth are conveyed to this 

 membrane. This membrane contains the sensory apparatus 

 which is stimulated by the vibrations. 



2. The sound-sensations. 



(a) The apparatus for the auditory sensations (Fig. 

 41). The septum of the cochlea canals consists of: 



i . The lamina spiralis ossea (Isd), \vhich extends from the 

 axis of the cochlea (modiolus) into the lumen of the cochlea 

 canal. 



