Figure 15.11. Bony labyrinth of the human inner ear. The cochlea (on the
right) is a coiled structure; cochlea derives from the Greek and Latin word for
snail shell or spiral shell. The vestibular fenestra (Latin fenestra = door) is the
location of the membrane of the oval window. The cochlear fenestra is the
location of the membrane of the round window, which allows the fluid inside
the cochlea to move, by bulging out and in as the sound vibration moves
through the cochlea. On the left side of the diagram are the three orthogonal
semicircular canals, described later in this chapter. The bony labyrinth mea-
sures about 1.25 centimeters along its long axis. This drawing is from the
1918 edition of Henry Gray’s Anatomy of the Human Body.
Along the length of the basilar membrane are several thousand
elegant little cells, called hair cells (Fig. 15.12). These cells are charac-
terized by a bundle of hairs or cilia attached to one end. As the basilar
membrane vibrates, the hair cells in the vicinity also vibrate, and their
cilia swoosh to and fro through the surrounding fluid. At the opposite
end of the cell from the bundle of cilia, the hair cell forms chemical
synapses with fibers of the auditory nerve, cranial nerve 8. The bend-