a. External Ear. The external ear consists of an auricle, or pinna, and an
external auditory meatus (a tube ending at the tympanic membrane or ear drum). The
auricle collects the sound vibrations in the air and sends them through the external
canal to the ear drum.
b. Tympanic Membrane. The tympanic membrane (see figure 1-6) is a tri-
layered membrane stretched across the end of the external meatus. The sound waves
come through the meatus and vibrate the membrane.
Figure 1-6. Landmarks of right tympanic membrane.
c. Middle Ear. Inside the tympanic membrane is a narrow, irregular, oblong,
air-conditioned cavity in the tympanic part of the temporal bone. This air-filled space
contains three small bones, which transfer the vibrations from the tympanic membrane
to the inner ear. Figure 1-7 shows the ossicles of the middle ear.
d. Inner Ear. The inner ear is a complex structure located in the petrous portion
of the temporal bone. It is made up of two distinct parts, each of which contains its own
kind of fluid. Sound vibrations carried by the bones of the inner ear are transferred by
way of the oval window to the fluid in the cochlea and received through a fine
membrane by the organ of Corti, the delicate neural end organ for sound. A second
function of the inner ear is the maintenance of balance, controlled by the movement of
fluid in the labyrinth in relation to neuroepithelial cells.
e. Temporal Bone. The temporal bone houses the middle and inner ear as well
as the mastoid sinuses.