Inion

Inion
Midsaggital section of a human skull. Inion indicated by yellow arrow.
X-ray of a human skull in lateral view. Inion indicated by yellow arrow.
Identifiers
Dorlands /Elsevier	i_08/12452346
TA	A02.1.00.018
FMA	76624
*Anatomical terms of bone* [edit on Wikidata]

The inion is the most prominent projection of the occipital bone at the posterioinferior (lower rear) part of the human skull. The ligamentum nuchae and trapezius muscle attach to it.

The term external occipital protuberance (protuberantia occipitalis externa) is sometimes used as a synonym, but more precisely the term "inion" refers to the highest point of the external occipital protuberance.

The inion is used as a landmark in the 10-20 system in EEG recording.

Etymology

The word ἰνίον (iníon) is the Greek word for the occipital bone.

Additional images

Side view of head, showing surface relations of bones. (Inion visible at center right.)

References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

Compound structures of skull

Neurocranium	Calvaria Diploë Asterion Pterion Stephanion Inion Bregma Lambda Fossae anterior middle posterior cranial cavity Base of skull Fontanelle anterior posterior sphenoidal mastoid

Facial skeleton	Nasion Gonion

Both	dacryon zygomatic arch temporal fossa infratemporal fossa pterygomaxillary fissure pterygopalatine fossa

The neurocranium of the skull

Occipital

Squamous part	external Inion/External occipital protuberance External occipital crest Nuchal lines planes Occipital Nuchal internal Cruciform eminence Internal occipital protuberance Sagittal sulcus Internal occipital crest Groove for transverse sinus

Lateral parts	Condyle Condyloid fossa Condylar canal Hypoglossal canal jugular Jugular process Jugular tubercle

Basilar part	Pharyngeal tubercle Clivus

Other	Foramen magnum Basion Opisthion

Parietal

Frontal

Squamous part	Frontal suture Frontal eminence external Superciliary arches Glabella foramina Supraorbital Cecum Zygomatic process internal Sagittal sulcus Frontal crest

Orbital part	Ethmoidal notch Fossa for lacrimal gland Trochlear fovea Frontal sinus Frontonasal duct

Temporal

Squamous part	Articular tubercle Suprameatal triangle Mandibular fossa Petrotympanic fissure Zygomatic process

Mastoid part	Mastoid foramen Mastoid process (Mastoid cells) Mastoid notch Occipital groove Sigmoid sulcus Mastoid antrum (Aditus)

Petrous part	Carotid canal Facial canal Hiatus Internal auditory meatus Cochlear aqueduct Stylomastoid foramen fossae Subarcuate fossa Jugular fossa canaliculi Inferior tympanic Mastoid Styloid process Petrosquamous suture (note: ossicles in petrous part, but not part of temporal bone)

Tympanic part	Suprameatal spine

Sphenoid

Surfaces	Superior surface: Sella turcica Dorsum sellae Tuberculum sellae Hypophysial fossa Posterior clinoid processes Ethmoidal spine Chiasmatic groove Middle clinoid process Petrosal process Clivus Lateral surface: Carotid groove Sphenoidal lingula Anterior surface: Sphenoidal sinuses

Great wings	foramina Rotundum Ovale Vesalii Spinosum Spine Infratemporal crest Sulcus for auditory tube

Small wings	Superior orbital fissure Anterior clinoid process Optic canal

Pterygoid processes	fossae Pterygoid Scaphoid pterygoid plates Lateral Medial Pterygoid canal Hamulus

Other	Body Sphenoidal conchae

Ethmoid

Plates	Cribriform plate Crista galli Olfactory foramina Perpendicular plate

Surfaces	Lateral surface Orbital lamina Uncinate process Medial surface Supreme nasal concha Superior nasal concha Superior meatus Middle nasal concha Middle meatus

Labyrinth	Ethmoid sinus ethmoidal foramina Posterior Anterior

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Inion

Etymology

Additional images

References

See also