The ear is the primary organ of hearing. It is divided into three parts: the external, middle, and inner ear (figs. 3-49 and 3-50).
Figure 3-49.The ear.
The external, or outer, ear is composed of two parts, the auricle and the external auditory canal. The auricle, or pinna, is a cartilaginous structure located on each side of the head. The auricle collects sound waves from the environment, which are then conducted by the external auditory canal to the eardrum. The lining of the auditory canal contains glands that secrete a waxy substance called cerumen. The cerumen aids in protecting the eardrum against foreign bodies and microorganisms.
Figure 3-50.The hearing process.
The eardrum, or tympanic membrane, is an oval sheet of fibrous epithelial tissue, 10 mm by 9 mm in size, which stretches across the inner end of the external auditory canal and separates the outer and middle ear. The sound waves cause the eardrum to vibrate. This vibration transfers the sounds from the external environment to the auditory ossicles.