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Skull - midsaggital section P.2005 - Inion.png
Midsaggital section of a human skull. Inion indicated by yellow arrow.
Schaedel im Röntgen seitlich - Inion.png
X-ray of a human skull in lateral view. Inion indicated by yellow arrow.
Gray's p.185
TA A02.1.00.018
FMA 76624
Anatomical terms of bone

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.


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

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