Porion
Encyclopedia
The porion is the point on the human skull
located at the upper margin of each ear canal
(external auditory meatus, external acoustic meatus). It underlies the targus. The anatomical landmark has significance in biological anthropology and craniometry.
. 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 orbitale (inferior margin of the left orbit)and the porion (upper margin of each ear canal) was most nearly parallel to the surface of the earth, and also close to 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
.
The determination of the Frankfort plane differs between skeletal and soft tissues, soft tissue using the targus as the landmark in place of the porion.
Human skull
The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...
located at the upper margin of each ear canal
Ear canal
The ear canal , is a tube running from the outer ear to the middle ear. The human ear canal extends from the pinna to the eardrum and is about 35 mm in length and 5 to 10 mm in diameter....
(external auditory meatus, external acoustic meatus). It underlies the targus. The anatomical landmark has significance in biological anthropology and craniometry.
Anatomical significance
The porion is one of the three anatomical points used to determine the Frankfurt planeFrankfurt plane
The Frankfurt plane was established at the World Congress on Anthropology in Frankfurt, Germany in 1884, and decreed as the anatomical position of the human skull...
. 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 orbitale (inferior margin of the left orbit)and the porion (upper margin of each ear canal) was most nearly parallel to the surface of the earth, and also close to the position the head is normally carried in the living subject.
In normal subjects, both orbitales
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
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
Asterion (anatomy)
The asterion is the point on the skull corresponding to the posterior end of the parietomastoid suture.-Location:In human anatomy, the asterion is a visible, so-called craniometric, point on the exposed skull, just behind the ear, where three cranial sutures meet:* the lambdoid,* parieto-mastoid,...
.
The determination of the Frankfort plane differs between skeletal and soft tissues, soft tissue using the targus as the landmark in place of the porion.