THE COCHLEA 



375 



endolvmph. and is continuous with the saccule, is called 

 the canalis cochlearis. The upper of the two cavities 

 containing perilymph, when traced d.nvu to the bottom of 

 the spiral, is found to be continuous with the cavity 

 containing perilymph which surrounds the vestibule ij.e 

 the utricle and saccule) ; hence it is called the scala 

 vestibuli. The lower cavity, when similarly traced to 

 the bottom of the spiral, ends at the fenestra rotunda, 

 which is closed bv a membrane. Since this lower cavity 

 is only separated from the middle ear or tympanum by 





Fio. 120. 



-A S2CTI0V THROrnH THE AXIS OF THE COCHI.EA 

 THBEK DIAMETERS. 



MAONIFIBD 



r r canalis cochlearis, or cochlear tube : Sc. r, scala vestibuli ; ScT 

 sca^-f 'tympani ; i S lamina spiralis ; Md. bony axis, or modiolus, round 

 which the scalJe are wound ; C. .V, cochlear nerve. 



the membrane covering the fenestra rotunda, it is called 

 the scala tympani. Thus the scala vestibuli and scala 

 tympani begin at different points, and are separated along 

 their whole course by the cochlear tube and the lamina 

 spiralis except at the very tip of the spiral, where tbese 

 latter end ; here the two seal* are prolonged beyond the 

 cochlear tube and join together, forming a common space, 

 as seen at the top of Fig. 120. 



The vibrations of sound are brought, as we shall see, 

 to the perilymph chamber of the vestibule, whence they 

 spread on *the other into the scala vestibuli. Passing 

 upwards, in the spiral along the scala vestibuli. they enter at 



