The tragus is a small pointed eminence of the
external ear
The outer ear, external ear, or auris externa is the external part of the ear, which consists of the auricle (anatomy), auricle (also pinna) and the ear canal. It gathers sound energy and focuses it on the eardrum (tympanic membrane).
Structur ...
, situated in front of the
concha, and projecting backward over the
. It also is the name of hair growing at the entrance of the ear. Its name comes from the
Ancient Greek
Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
(), meaning 'goat', and is descriptive of its general covering on its under surface with a tuft of
hair
Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals.
The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and ...
, resembling a
goat
The goat or domestic goat (''Capra hircus'') is a species of Caprinae, goat-antelope that is mostly kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the ...
's
beard
A beard is the hair that grows on the jaw, chin, upper lip, lower lip, cheeks, and neck of humans and some non-human animals. In humans, beards are most commonly seen on pubescent or adult males, though women have been observed with beards ...
.
The nearby
antitragus
The antitragus is a feature of mammalian ear anatomy.
In humans, it is a small Tubercle (anatomy)#Ears, tubercle on the visible part of the ear, the Auricle (anatomy), auricle. The antitragus is located just above the earlobe and points anatomical ...
projects forwards and upwards.
Because the tragus faces rearwards, it aids in collecting sounds from behind. These sounds are delayed more than sounds arriving from the front, assisting the brain to sense front vs. rear sound sources.
In a positive
fistula
In anatomy, a fistula (: fistulas or fistulae ; from Latin ''fistula'', "tube, pipe") is an abnormal connection (i.e. tube) joining two hollow spaces (technically, two epithelialized surfaces), such as blood vessels, intestines, or other h ...
test (for the presence of a fistula from
cholesteatoma
Cholesteatoma is a destructive and expanding growth consisting of keratinizing squamous epithelium in the middle ear and/or mastoid process. Cholesteatomas are not cancerous as the name may suggest, but can cause significant problems because of the ...
to the
labyrinth
In Greek mythology, the Labyrinth () is an elaborate, confusing structure designed and built by the legendary artificer Daedalus for King Minos of Crete at Knossos. Its function was to hold the Minotaur, the monster eventually killed by the h ...
), pressure on the tragus causes
vertigo
Vertigo is a condition in which a person has the sensation that they are moving, or that objects around them are moving, when they are not. Often it feels like a spinning or swaying movement. It may be associated with nausea, vomiting, perspira ...
or eye deviation by inducing movement of
perilymph
Perilymph is an extracellular fluid located within the inner ear. It is found within the scala tympani and scala vestibuli of the cochlea. The ionic composition of perilymph is comparable to that of plasma and cerebrospinal fluid. The major ca ...
.
Other animals
The tragus is a key feature in many bat species. As a piece of skin in front of the ear canal, it plays an important role in directing sounds into the ear for prey location and navigation via
echolocation.
[Chiu, C., & Moss, C. F. (2007). The role of the external ear in vertical sound localization in the free flying bat, Eptesicus fuscus. The Journal of the Acoustical Society of America, 121(4), 2227–2235.] Because the tragus tends to be prominent in bats, it is an important feature in identifying bat species.
The tragus allows echolocating bat species to vertically discriminate the objects around them, which is key to identifying where prey items and obstacles are in three-dimensional space.
In studies where an individual's tragi are temporarily glued out of their normal positions, the bat's navigational acuity is one-fourth as effective as individuals with unmodified tragi.
Based on this study, the authors concluded that the tragus's function is to create acoustic cues to determine the direction of a target in the vertical plane.
Not all echolocating bats possess tragi, however.
Horseshoe bat
Horseshoe bats are bats in the family Rhinolophidae. In addition to the single living genus, ''Rhinolophus'', which has about 106 species, the extinct genus '' Palaeonycteris'' has been recognized. Horseshoe bats are closely related to the Ol ...
s are one such family; the way in which the outer bottom edge of the ear folds in on itself is thought to function in a similar way to the tragus in other families.
Additional images
File:Gray908.png, Horizontal section through left ear; upper half of section.
File:Slide2COR.JPG, External ear. Right auricle. Lateral view.
File:Slide4COR.JPG, External ear. Right auricle. Lateral view.
See also
*
Auricular branch of the vagus nerve
*
Tragal pressure
*
Tragus piercing
References
External links
*
* () (#7)
{{Authority control
Ear
Otorhinolaryngology