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 membrane to bulge inward, and to be stretched so tight that it cannot vibrate freely.

The inner ear is called the labyrinth, because of its winding passages. There is a spiral passage called the snail shell and three simpler passages called the loops (Fig. 128). The inner ear is filled with a limpid liquid which conveys the vibrations to the ends of the auditory nerve found in the snail shell. If the auditory nerve or labyrinth becomes diseased, the deafness is probably incurable. Quinine and other drugs may cause deafness.

Sense of Equilibrium.—Some fibers of the auditory nerve end in the loops and are not believed to be used in hearing. It is believed that each loop acts like a carpenter's level, and the varying pressure of the fluid upon the nerves in the loops tells us the position of the body and constitutes the sense of equilibrium. There are how many of these loops in each ear? (Fig. 128.)