THE LARYNX AND THE EAR 363 



The Scala Vestibula and the Scala Tympani appear in 

 cross section as the larger of the canals. The former t 

 ,so named from its connection with the vestibule, occupies 

 the upper position in all parts of the coil. The latter lies 

 below at all places, and is separated from the channels 

 above partly by a margin of bone and partly by a mem- 

 brane. It receives its name from its termination at the 

 tympanum, or middle ear, from which it is separated only 

 by a thin membrane. 1 Both the scala vestibula and the 

 scala tympani belong to the outer portion of the internal 

 ear and are, for this reason, filled with the perilymph. At 

 their upper ends they communicate with each other by a 

 small opening, making by this means one continuous canal 

 through the cochlea. This canal passes from the vesti- 

 bule to the tympanum and, in so doing, goes entirely 

 around 



The Scala Media. This division of the cochlea lies 

 parallel to and between the other two divisions. It is 

 above the scala tympani and below the scala vestibula, 

 and is separated from each by a membrane. The scala 

 media belongs to the membranous portion of the internal 

 ear and is, therefore, filled with the endolymph. It receives 

 the terminations of fibers from the auditory nerve and may 

 be regarded as the true sense organ of hearing. The nerve 

 fibers terminate upon the membrane known as the basilar 

 membrane, which separates it from the scala tympani. 

 This membrane extends the length of the cochlear canals, 

 and is stretched between a projecting shelf of bone on one 

 side and the outer wall of the cochlea on the other. It is 

 covered with a layer of epithelial cells, some of which have 

 small, hair-like projections and are known as the hair cells. 

 Above the membrane, and resting partly upon it, are two 



i A small opening in the bone at this place is called \\iefenestra rotunda. 



