Theouter ear,external ear, orauris externa is the external part of theear, which consists of theauricle (also pinna) and theear canal.^[1] It gathers sound energy and focuses it on the eardrum (tympanic membrane).

Outer ear
A diagram of the anatomy of the human ear:   Brown isouter ear.   Red ismiddle ear.   Purple isinner ear.
The auricula. Lateral surface.
Details
Identifiers
Latin	auris externa
MeSH	D004431
NeuroLex ID	birnlex_1705
TA98	A15.3.01.001
TA2	6862
FMA	52781
Anatomical terminology [edit on Wikidata]

The visible part is called theauricle, also known as thepinna, especially in other animals. It is composed of a thin plate of yellowelastic cartilage, covered with integument, and connected to the surrounding parts by ligaments and muscles; and to the commencement of theear canal by fibrous tissue. Manymammals can move the pinna (with the auriculares muscles) in order tofocus their hearing in a certain direction in much the same way that they can turn theireyes. Most humans do not have this ability.^[2]

From the pinna, thesound waves move into theear canal (also known as theexternal acoustic meatus) a simple tube running through to themiddle ear. This tube leads inward from the bottom of the auricula and conducts the vibrations to the tympanic cavity and amplifies frequencies in the range 2 kHz to 5 kHz.^[3]

Theintrinsic auricular muscles are:

• Thehelicis major is a narrow vertical band situated upon the anterior margin of thehelix. It arises below, from thespina helicis, and is inserted into the anterior border of the helix, just where it is about to curve backward.
• Thehelicis minor is an obliquefasciculus, covering thecrus helicis.
• Thetragicus is a short, flattened vertical band on the lateral surface of thetragus. Also known as the mini lobe.
• Theantitragicus arises from the outer part of the antitragus, and is inserted into thecauda helicis andantihelix.
• Thetransverse muscle is placed on the cranial surface of thepinna. It consists of scattered fibers, partly tendinous and partly muscular, extending from theeminentia conchae to the prominence corresponding with thescapha.
• Theoblique muscle also on the cranial surface, consists of a few fibers extending from the upper and back part of theconcha to the convexity immediately above it.

The intrinsic muscles contribute to the topography of the auricle, while also function as a sphincter of the external auditory meatus. It has been suggested that during prenatal development in the womb, these muscles exert forces on the cartilage which in turn affects the shaping of the ear.^[4]

Theextrinsic auricular muscles are the threemuscles surrounding theauricula or outer ear:

• anterior auricular muscle
• superior auricular muscle
• posterior auricular muscle

The superior muscle is the largest of the three, followed by the posterior and the anterior.

In some mammals these muscles can adjust the direction of the pinna. In humans these muscles possess very little action.The auricularis anterior draws the auricula forward and upward, the auricularis superior slightly raises it, and the auricularis posterior draws it backward. The superior auricular muscle also acts as a stabilizer of theoccipitofrontalis muscle and as a weak brow lifter.^[5] The presence of auriculomotor activity in the posterior auricular muscle causes the muscle to contract and cause the pinna to be pulled backwards and flatten when exposed to sudden, surprising sounds.^[6]

One consequence of the configuration of the outer ear is selectively to boost thesound pressure 30- to 100-fold for frequencies around 3 kHz. This amplification makes humans most sensitive to frequencies in this range—and also explains why they are particularly prone to acoustical injury and hearing loss near this frequency. Most human speech sounds are also distributed in the bandwidth around 3 kHz.^[7]

Malformations of the external ear can be a consequence ofhereditary disease, or exposure to environmental factors such asradiation,infection. Such defects include:

• Apreauricular fistula, which is a long narrow tube, usually near thetragus. This can be inherited as anautosomal recessive fashion and may suffer from chronic infection in later life.^[8]
• Cosmetic defects, such as very large ears, small ears.^[9][10]
• Malformation that may lead to functional impairment, such asatresia of the external auditory meatus^[11] oraplasia of the pinna,^[12]
• Geneticsyndromes, which include:
  • Konigsmark syndrome, characterised by small ears and atresia of the external auditory canal, causingconductive hearing loss and inherited in anautosomal recessive manner.^[13]
  • Goldenhar syndrome, a combination of developmental abnormalities affecting the ears, eyes, bones of the skull, and vertebrae, inherited in anautosomal dominant manner.^[14]
  • Treacher Collins syndrome, characterised by dysplasia of the auricle, atresia of the bony part of the auditory canal, hypoplasia of the auditory ossicles and tympanic cavity, and 'mixed' deafness (bothsensorineural and conductive), inherited in an autosomal dominant manner.^[15][16]
  • Crouzon syndrome, characterised by bilateral atresia of the external auditory canal, inherited in anautosomal dominant manner.^[17]

Usually, malformations are treated with surgery, although artificial prostheses are also sometimes used.^[10]

• Preauricular fistulas are generally not treated unless chronically inflamed.^[10]
• Cosmetic defects without functional impairment are generally repaired after ages 6–7.^[18]

If malformations are accompanied by hearing loss amenable to correction, then the early use ofhearing aids may prevent complete hearing loss.^[18]

The outer ear's cartilage is homologous to the cartilage ingills of amphibians, fishes, and invertebrates such as thehorseshoe crab. The extracolumella cartilage of reptiles is likely also homologous.^[19]

•  
  External and middle ear, opened from the front. Right side.

 This article incorporates text in thepublic domain frompage 1033 of the 20th edition ofGray's Anatomy(1918)

  Media related toOuter ear at Wikimedia Commons