posterior
Meaning of posterior: Nothing is posterior on its own, since the word only carries meaning once a second structure is named for comparison.
Definition of posterior
Posterior is a directional term meaning toward the back of the body or of a structure, and it is always stated in relation to something else. The spine is posterior to the breastbone; the heel is posterior to the toes. Anatomical directions are read from the anatomical position, a person standing upright, facing forward, arms at the sides with the palms turned out.
How do the directional pairs work?
Anatomical direction words come in opposing pairs, and each pair covers one axis of the body. Using them removes the ambiguity of everyday words such as above or behind, which change meaning the moment a person lies down.
| Term | Opposite | Meaning |
|---|---|---|
| Posterior | Anterior | Toward the back, versus toward the front |
| Superior | Inferior | Toward the head, versus toward the feet |
| Medial | Lateral | Toward the midline, versus away from it |
| Proximal | Distal | Nearer the trunk, versus further along a limb |
| Superficial | Deep | Nearer the surface, versus further inside |
Is posterior the same as dorsal?
For the human trunk and head the two are used interchangeably, so the back of the chest can be called posterior or dorsal without confusion. They separate at the limbs. The dorsum of the hand does face backward in the anatomical position, but the dorsum of the foot faces upward and forward, so dorsal there is nearer to superior than to posterior. The terms also diverge across species: in a four-legged animal, dorsal means toward the spine while posterior means toward the tail. Comparative anatomy keeps both words for that reason.
Where does the word appear in practice?
It labels structures, positions and views. Named structures include the posterior cruciate ligament of the knee and the posterior cerebral artery. On a chest radiograph, posteroanterior describes a beam passing from back to front, which is not the same image as an anteroposterior film taken the other way round, because structures nearer the detector appear sharper and closer to true size. In an examination note, posterior localizes a finding precisely, so that tenderness behind the shoulder is not confused with tenderness in front of it.
Used in a sentence
Tenderness was noted along the posterior shoulder.
Good to know
Posterior and dorsal are often used interchangeably for the trunk, but they are not equivalent everywhere, since the dorsum of the foot faces upward rather than backward and dorsal means toward the spine in four-legged animals.
Word origin
Where “posterior” comes from
From Latin posterior, meaning coming after or behind, the comparative form of posterus, meaning following.