What Is the Inion?

The inion is the most noticeable or pronounced protrusion of the occipital bone, which is one of the bones that comprise the skull. In fact, the name “inion” is a Greek term that is actually used for the occipital bone. Thus, in some cases, synonyms like “occipital bone,” among others, are used for the protrusion, even if they are not entirely accurate.

Forming part of the much larger, upper part of the human skull, called the cranium, the occipital bone is shaped like a saucer, or a trapezoid with curved ends. It is located at the cranium’s rear and lower regions. The occipital bone has a scale-like structure called the occipital squama, near the middle of the external occipital protuberance.

The inion is located at the external occipital protuberance. Thus, the protrusion is sometimes referred to as the external occipital protuberance. The inion, however, is the highest point of this particular area of the occipital bone. It is not synonymous with the external occipital protuberance itself.

Two types of muscles are attached to the inion: the ligamentum nuchae and the trapezius muscle. Also known as the nuchal ligament, or paxwax, the ligamentum nuchae is one of the strong fibrous cords of the neck. It is named after the median nuchal line, which is one of the occipital bone’s four external curved lines that runs from the external occipital protuberance. The other type of muscle attached to the bump, the trapezius, runs lengthwise to the middle section of the spine. The trapeziuses are responsible for moving the scapulae, or shoulder blades, enabling movement of the head and providing support to the arms.

The inion is also anatomically notable for being referred to as an Anatolian bump, which is when the inion is larger than usual. The protrusion gets its name from the alleged high number of occurrences among the people of Anatolia — the westernmost region of Asia, which is mostly covered by the Republic of Turkey. There is no research or proof, however, to substantiate that contention, nor is this variant of the inion restricted to the Anatolian region. Legend has it that in Nazi Germany, the protrusion was considered an indication of membership of the “master race” or “Aryan race,” a concept of white supremacy especially dominant in the late 19th and early 20th centuries. Additionally, some Swedes consider the bump as the mark of descendants of Walloons, some of who migrated to Sweden from Belgium as early as the 17th century.