Corpus: Auricle

The auricle is the outer part of the ear, formed from cartilage tissue and covered with skin, which acts as a sound funnel.

The auricle is fused to the periosteum of the skull (pericranium). The shape of the auricle is characterised by the auricular cartilage (cartilago auriculae), which consists of one piece. It consists of elastic cartilage.

2.1. Topography

The auricle is located on both sides in the auricular region of the same name. As it is a prominent reference point, structures located in front of the auricle are referred to as preauricular and those located behind it as retroauricular.

2.2. Morphology

The ear cartilage is strongly folded, resulting in a typical ear relief with numerous elevations and depressions, each of which has its own name. The prominent outer edge of the auricle is called the helix. Parallel to the helix - separated by a narrow curved indentation called the scapha - runs the crescent-shaped anthelix as a prominent bulge. At its cranial end it divides into two separate folds, the upper (crus superius anthelicis) and lower anthelical root (crus inferius anthelicis). Between them lies a triangular indentation, the triangular fossa.

The anthelix frames the actual "auricle" (concha auricularis), an extensive depression. It is separated into two parts by an extension of the helix (crus helicis), the cranial cymba conchae ("conchal bowl") and the caudal cavum conchae ("conchal cavity"), which represents the transition to the external auditory canal (meatus acusticus externus). Two protrusions can be recognised laterally in front of the cavum conchae: The rostrally located tragus (ear cover) and the dorsally located antitragus. The incisura intertragica lies between the tragus and antitragus. Caudal to the tragus is the earlobe (lobulus auriculae), which is free of cartilage.

The tuberculum auriculae (Darwin's tubercle) is an irregular triangular protrusion of the edge of the helix. It corresponds to the tip of the previously pointed mammalian ear in the sense of an atavism.

The facies medialis of the pinna is significantly less structured than the outer side (facies lateralis). The concha, triangular fossa and scapha appear as protrusions of the same name (eminentiae).

2.3. Ligaments

The auricle is attached to the bone by three ligaments (ligamenta auricularia):

• Ligamentum auriculare anterius: runs from the spina helicis to the root of the zygomatic process
• Ligamentum auriculare superius: runs from the upper edge of the external auditory canal cartilage to the pars squamosa ossis temporalis
• Posterior auricular ligament: runs from the back of the concha to the mastoid process of the temporal bone

2.4. Muscles

The auricular muscles are divided into intrinsic and extrinsic muscles. Four intrinsic striated muscle bundles connect and stabilise the auricle on the lateral surface (Musculi helicis major and minor, Musculus tragicus, Musculus antitragicus) and two on the medial surface (Musculus transversus and obliquus auriculae).

The extrinsic muscles can move the auricle slightly and are part of the mimic musculature. The anterior and superior auricularis muscles insert at the spina helicis, the upper one additionally at the eminentia fossae triangularis of the facies medialis. The posterior auricularis muscle inserts on the eminentia conchae on the medial side. The three muscles originate from the head ridge (anterior and superior) or from the mastoid region (posterior).

The muscles of the outer ear are innervated by the facial nerve, the lateral side by the temporal rami and the medial side by the posterior auricular nerve.

2.5. Innervation

The sensory innervation of the auricle is provided by various nerves. The medial side is supplied by the cervical plexus:

• Auricularis magnus nerve (lower two-thirds)
• minor occipital nerve (upper third)

The lateral side is innervated by:

• auricularis magnus nerve (posterior sections)
• Rami auriculares of the vagus nerve: concha and cymba
• auriculotemporal nerve from the mandibular nerve of the trigeminal nerve: anterior sections of the helix, tragus and earlobe
• Posterior auricular nerve from the facial nerve: ring-shaped area around the concha
• Ramus communicans cum nervo vagi from the glossopharyngeal nerve: entrance area of the external auditory canal

2.6. Blood supply

The arterial blood supply to the medial side of the auricle is provided by the auricular ramus of the posterior auricular artery from the external carotid artery or occipital artery. The lateral facies is supplied by branches of the medial side, which perforate the auricle, and by the anterior auricular rami from the superficial temporal artery.

2.7. Lymph drainage

The lymph flows to the Nodi lymphatici parotidei (anterior sections) and Nodi lymphatici cervicales profundi and Nodi lymphatici occipitales (remaining sections).

2.8. Histology

The cartilago auriculae consists of elastic cartilage with fibrocartilage components. It is covered by multilayered keratinised squamous epithelium. The dermis is fused with the perichondrium, subcutaneous fatty tissue is largely absent. The earlobe consists of a lot of fatty tissue and coarse connective tissue strands.

Lanugo hairs, sebaceous glands and sweat glands are found all over the outer ear, especially in the concha and scaphoid fossa. Longer bristle-shaped hairs (tragi) are also found in the opening and the cartilage section of the external auditory canal. In the tragus and antitragus area, tufts of terminal hairs can develop at an older age, which are known as barbula hirci (goat's beard).

The relief of the auricle with its folds and depressions is a natural filter system for incoming sound. The sound is refracted at the relief edges of the pinna and thus - depending on its frequency components - attenuated differently. From this modulation, the brain can obtain information about the spatial origin of a sound source, in particular whether a sound comes from the front, back, above or below (directional hearing).

Trauma to the auricle (e.g. injuries, insect bites, piercings, frostbite or surgery) can lead to an othaematoma with subsequent inflammation of the auricular tissue, which is known as auricular perichondritis. Another common disease of the pinna is chondrodermatitis nodularis helicis.

• Ear cysts
• Ear appendages
• Auricular fistulae
• Auricular dysplasia
• Microtia
• Apostasis otum (often due to a strong curvature of the concha and too weak angulation of the anthelix)C