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Figure 3-47.—Eye, ophthalmoscope view. | Up
Hospital Corpsman 3 & 2 - Intro Navy Nursing manual for hospital training purposes | Next
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Figure 3-49.—The ear.
Figure 3-50.—The hearing process.
HEARING
to the eardrum. The lining of the auditory canal
contains glands that secrete a waxy substance
The ear is the primary organ of hearing. It is
called cerumen. The cerumen aids in protecting
divided into three parts: the external, middle, and
the eardrum against foreign bodies and
inner ear (figs. 3-49 and 3-50).
microorganisms.
External Ear
The eardrum, or tympanic membrane, is an
oval sheet of fibrous epithelial tissue, 10 mm by
The external, or outer, ear is composed of two
9 mm in size, which stretches across the inner end
parts, the auricle and the external auditory canal.
of the external auditory canal and separates the
The auricle, or pinna, is a cartilaginous structure
outer and middle ear. The sound waves cause the
located on each side of the head. The auricle col-
eardrum to vibrate. This vibration transfers the
lects sound waves from the environment, which
sounds from the external environment to the
are then conducted by the external auditory canal
auditory ossicles.
3-38
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