The porion is the point on the

human skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominen ...

located at the upper margin of each

ear canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the auricle to the eardrum and is about in length and in diameter. S ...

(external auditory meatus, external acoustic meatus). It lies on the superior margin of the tragus. It is a cephalometric landmark with significance in

biological anthropology Biological anthropology, also known as physical anthropology, is a natural science discipline concerned with the biological and behavioral aspects of human beings, their extinct hominin ancestors, and related non-human primates, particularly fro ...

and in clinical applications such as

oral and maxillofacial surgery Oral and maxillofacial surgery (OMFS) is a surgical specialty focusing on reconstructive surgery of the face, facial trauma surgery, the Human mouth, mouth, Human head, head and neck, and jaws, as well as facial plastic surgery including clef ...

Anatomical significance

The porion is one of the three anatomical points used to determine the Frankfurt plane. The Frankfurt plane (also called the auriculo-orbital plane) was established at the World Congress on Anthropology in Frankfurt, Germany in 1884, and decreed as the anatomical position of the human skull for comparative craniometric measurements. It was decided that a plane passing through the inferior margin of the left

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

(the point called the left orbitale) and the upper margin of each ear canal or external auditory meatus, a point called the porion, was most nearly parallel to the surface of the

earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

at the position the head is normally carried in the living subject. In normal subjects, both orbitales and both porions lie in a single plane. However, due to pathology, this is not always the case. The formal definition specifies only the three points listed above, sufficient to describe a plane in three-dimensional space. The Mastoid Index (a craniometric measurement) is the distance from the porion to the

asterion In Greek mythology, Asterion (Ancient Greek, Greek: , gen.: , literally "starry") or Asterius () may refer to the following figures: * Asterion (god), Asterion, one of the River gods (Greek mythology), river gods. * Asterius (giant), Asterius ...

. The determination of the Frankfort plane differs between skeletal and soft tissues, soft tissue using the tragus as the landmark in place of the porion.Ferrario, V.F. et al., 1995. Relative position of porion and tragus in orthodontic patients. Clinical Anatomy, 8(5), 352-358.

Additional Images

File:Slide3ROM.JPG, The porion. Human skull.

References

{{Reflist Skull