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(also auricle or auricula), the external part of the human and mammalian auditory analyser, consisting of elastic cartilage and a skin covering. The cartilage determines the pinna’s shape and its various elevations and depressions, such as the helix (the pinna’s incurved margin), the antihelix (located parallel to the helix), the tragus (the anterior protuberance), the antitragus (located behind the tragus), and the fossa triangularis. The lobe has no cartilage. Deep within the pinna, directly behind the tragus, is the opening of the external auditory canal. The pinna’s skin is covered with minute hairs and contains sebaceous and sudoriferous glands.
In some mammals, the pinna is endowed with special musculature and is capable of movement; in others, individual parts of the pinna are capable of movement; and in still others, for example, humans, movement is severely limited. The pinna is secondarily simplified or completely reduced in many aquatic mammals, such as whales, manatees, seals, and walruses, and in many burrowing animals, such as desmans and moles. It is well developed in nocturnal animals, for example, bats, in some forest ungulates, and in desert canids.
The pinna has many functions. It receives sound and amplifies or reflects it according to frequency. It makes possible the determination of the spatial location of a sound source. It also protects the auditory organs from mechanical injury during digging and diving, as well as from excessive noise, by means of special protective hairs, by the overlapping of the auditory canal, or by the involution of the entire pinna, as in some bats.
G. N. SIMKIN