''For people with the surname, see

Porion (surname) Porion is a French surname French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic g ...

.'' The porion is the point on the

human skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

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 pinna to the eardrum and is about in length and in diameter. Struc ...

(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 scientific discipline concerned with the biological and behavioral aspects of human beings, their extinct hominin ancestors, and related non-human primates, particularly from an e ...

and in clinical applications such as oral and maxillofacial surgery.

Anatomical significance

The porion is one of the three anatomical points used to determine the

Frankfurt plane The standard anatomical position, or standard anatomical model, is the scientifically agreed upon reference position for anatomical location terms. Standard anatomical positions are used to standardise the position of appendages of animals with r ...

. 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 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 object or position in space such as a p ...

(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 harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

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 (Greek: , gen.: , literally "starry") or Asterius () may refer to the following figures: * Asterion, one of the Potamoi. * Asterius, one of the Giants. * Asterion, an attendant of the starry-god Astraeus. * Aster ...

. 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