Anatomical position and directional terms

Anatomical position is the standard reference posture used to describe the human body: standing upright, facing forwards, with the arms at the sides and the palms facing forwards. Directional terms describe where one structure lies relative to another, using this reference even when the body is sitting, lying down or moving.

What is the standard anatomical position?

In anatomical position, the body is upright, the head is level, and the face and eyes point forwards. The lower limbs are straight, with the feet directed forwards. The arms hang at the sides, with the palms facing forwards and the thumbs pointing away from the body.

The essential features are:

• The head and body face forwards.
• The upper limbs rest alongside the body.
• The palms face forwards, rather than towards the thighs.
• The thumbs point outwards, away from the centre of the body.
• The feet point forwards.

This is a reference posture, not a description of how people must normally stand. A person’s actual posture may differ, but anatomical descriptions still use the standard position unless another reference is explicitly stated.

Why do anatomists use a reference position?

A shared reference prevents the meaning of a description from changing whenever the body moves. Without it, words such as “above”, “behind” or “outside” could depend on the observer’s viewpoint or the subject’s posture. Anatomical directional terms instead describe consistent relationships within the body.

For example, the front of the body remains its anterior surface when a person lies face down. “Anterior” means towards the front in anatomical position; it does not mean towards the ceiling or towards the observer. Likewise, a structure described as superior remains towards the head in the anatomical reference, even when the person is lying horizontally.

Most directional statements are comparisons. Saying that one structure is anterior to another gives a relationship between them, rather than an absolute location. The same structure can be anterior to one neighbour and posterior to another.

What do the paired directional terms mean?

The terms below describe different aspects of position. The midline is an imaginary line through the centre of the body that separates its right and left sides. Attachment here means the connection of a limb to the trunk, the central part of the body containing the chest, abdomen and pelvis.

These pairs are not interchangeable. Superior and inferior describe the head-to-foot direction, whereas superficial and deep describe distance from the body surface. A structure can therefore be both inferior to one structure and deep to another without any contradiction.

How do you use directional terms in a sentence?

A clear anatomical sentence names a structure, gives a directional term, and identifies the structure used for comparison. A useful pattern is: “Structure A is [directional term] to structure B.” Where a structure occurs on both sides of the body, add left or right if the comparison requires it.

Examples include:

• The sternum is anterior to the vertebral column.
• The heart is posterior to the sternum.
• The skin is superficial to the humerus.
• The right femur is contralateral to the left humerus.

Reversing a comparison usually requires the opposite term. If the sternum is anterior to the heart, the heart is posterior to the sternum. Similarly, if the skin is superficial to the humerus, the humerus is deep to the skin.

Not every relationship fits neatly into a single direction. Structures have length, width and irregular shapes, so a precise description may need to identify a particular part. “The distal end of the humerus” identifies its end nearer the elbow, rather than treating the entire bone as a single point.

When should you use proximal and distal?

Proximal and distal are especially useful for describing limbs. They follow the limb from its attachment to the trunk towards its free end. The shoulder end of the humerus is proximal, while its elbow end is distal; the hip end of the femur is proximal, while its knee end is distal.

These terms remain useful when a limb is bent or raised. The wrist is distal to the elbow even when the hand is held above the head. Calling the wrist “superior” in that situation would describe its temporary height, not its position along the limb in the standard reference.

Avoid defining proximal simply as “closer to the centre of the body”. For limb anatomy, the relevant reference is the limb’s attachment to the trunk. Proximal and distal can also describe positions along other structures, but the starting point must be clear from the context.

How do left, right, ipsilateral and contralateral differ?

Left and right always belong to the subject being described. When facing a person who is in anatomical position, their right side is on your left. Turning around the person or viewing them from behind does not change their anatomical right and left.

Ipsilateral and contralateral compare sides rather than distances. The right upper limb and right lower limb are ipsilateral because both belong to the right side. The right upper limb and left lower limb are contralateral because they belong to opposite sides.

These terms do not mean that structures are close together, touching or at the same level. Two structures can be far apart and still be ipsilateral. Neither term replaces anterior, medial or proximal: each answers a different question about the relationship.

What mistakes should you avoid when learning these terms?

The most common errors come from changing the reference without noticing. Keep the subject’s anatomical position in mind, rather than letting the page, screen or viewing angle determine the description.

• Using the observer’s left and right: identify the subject’s side before naming a paired structure.
• Turning the palms towards the thighs: in anatomical position, the palms face forwards and the thumbs point outwards.
• Treating medial as “inside”: medial means towards the midline, not necessarily deeper beneath the skin.
• Treating lateral as “superficial”: lateral means away from the midline, not closer to the body surface.
• Using proximal as a synonym for superior: proximal follows the limb towards its attachment, regardless of how the limb is held.
• Leaving out the comparison: “anterior to the sternum” gives a clearer relationship than “anterior” alone.

In the 3D model next to this article, you can rotate and zoom, select a structure, and isolate it. After changing the viewing angle, practise describing the same relationship again: the observer’s view changes, but the anatomical terms do not.