Anatomical Terminology: Standard Directions and Planes of the Body

In the fields of medicine and biology, precision is paramount. To describe the location of organs, tissues, and structures without ambiguity, professionals use standard anatomical terms of location. These terms, primarily derived from Latin and Greek roots, provide a universal language that ensures a clinician in one part of the world understands exactly what a colleague in another part means when describing a patient's anatomy.

These descriptors are based on the standard anatomical position, a consistent reference point that defines what constitutes the front, back, top, and bottom of an organism. By establishing this baseline, the body can be mapped using specific planes and axes.

A male and female human in the standard anatomical position

Key Facts

Because of differences in the way humans and other animals are structured, different terms are used according to the neuraxis and whether an animal is a vertebrate or invertebrate.

Standard Anatomical Position: The universal reference point used to define directional terms.
Planes: Imaginary flat surfaces (frontal, sagittal, transverse) used to section the body.
Axes: Lines around which the body rotates or is measured (e.g., craniocaudal, anteroposterior).
Species Variation: Terms change based on whether an animal is a biped (two-legged) or quadruped (four-legged) due to the neuraxis (the imaginary line connecting the brain and spinal cord).
Non-Bilaterians: Organisms without a symmetrical left/right side use terms like proximal and distal relative to their center.

Anatomical Planes and Axes

To navigate the complex geometry of the body, anatomists use three primary plane orientations and corresponding axes.

The Three Main Planes

Planes are used to slice the body into sections for imaging or description. These include the frontal (coronal), sagittal, and transverse planes.

The standard anatomical planes of both a human and a goat displaying three anatomical planes:

The Primary Axes

Left-Right Axis: Also known as the horizontal or frontal axis.
Craniocaudal Axis: Also referred to as the rostrocaudal, longitudinal, or cephalocaudal axis.
Anteroposterior Axis: Also known as the dorsoventral or sagittal axis.

While these axes apply to humans and most vertebrates, organisms with spherical or asymmetrical body plans may utilize different axial systems.

Anatomical axes in a human, similar for other orthograde bipedal vertebrates

Essential Directional Terms

Directional terms allow for the precise description of one structure relative to another. Many of these terms come in opposite pairs.

Vertical and Longitudinal References

In humans, superior (or cranial) describes a position nearer to the head, while inferior (or caudal) describes a position nearer to the feet. For example, the superior mediastinum is located above the inferior mediastinum.

In veterinary anatomy, superior and inferior are generally reserved for the eyes, eyelids, lips, and inner ear; instead, dorsal and ventral are used for the rest of the body.

Front and Back

Anterior refers to the front, and posterior refers to the back. In neuroanatomy and embryology, the terms ventral (belly side) and dorsal (back side) are frequently used. In humans, ventral is typically anterior, and dorsal is posterior.

Midline and Side

Medial: Closer to the midline of the body.
Lateral: Further from the midline.
Contralateral: On the opposite side of the body (e.g., the left brain controls the contralateral right arm).
Unilateral: Affecting only one side of the body.

Special terms like varus (bowing toward the midline) and valgus (bowing away from the midline) describe specific joint angulations in the coronal plane.

Proximity to the Center

Proximal describes a part closer to the main mass of the body (the chest or heart), while distal describes a part further away. For instance, the shoulder is proximal to the hand.

Anatomical terms used to describe a human hand

Specialized Anatomical Terms

Neuroanatomy and Head Terms

Because the human brain curves, the terms rostral (toward the nose) and caudal (toward the tail/back) are adapted to the C-shaped neuraxis of Hominidae.

In the human skull, the terms rostral and caudal are adapted to the curved neuraxis of Hominidae, rostrocaudal meaning the region on C shape connecting rostral and caudal regions.

Depth and Centrality

Central vs. Peripheral: Central refers to the core (e.g., central nervous system), while peripheral refers to the surface or extremities.
Superficial vs. Deep: Superficial describes structures near the skin's surface, whereas deep describes those further inside.

Dorsolateral prefrontal cortex highlighted in dark green

Modifiers and Combined Terms

Anatomical terms are often modified by prefixes to provide more detail:

Sub-: Beneath (e.g., subcutaneous).
Infra-: Below (e.g., infraorbital).
Inter-: Between (e.g., intercostal).
Supra- / Super-: Above (e.g., supraorbital).
Ab-: Away from (e.g., abduction).
Ad-: Toward (e.g., adduction).

Terms can also be combined, such as the proximodistal axis, which describes the length of an appendage from its attachment point to its tip.

Terms can be modified with prefixes and suffixes. In this image showing the jellyfish species Chrysaora, the prefix 'ab-', is used to indicate something that is 'away from' the mouth, for example the aboral. Other terms are combined to indicate axes, such as proximodistal axis.

Comparative Anatomy and Special Cases

Anatomical language adapts to the body plan of the organism:

Non-Bilaterians: Organisms like jellyfish or sponges lack a left/right symmetry. They may use oral (near the mouth) and aboral (away from the mouth) or apical-basal axes.
Elongated Organisms: Organisms like Paramecium have distinct ends to their long axis.
Asymmetrical/Spherical: Amoeboid organisms may have entirely different axial definitions.

Asymmetrical and spherical body shapes. (a) An organism with an asymmetrical, amoeboid body plan (Amoeba proteus – an amoeba). (b) An organism with a spherical amoeboid body plan (Actinophrys sol – a heliozoan).

Four individuals of Phaeodactylum tricornutum, a diatom with a fixed elongated shape

Organisms where the ends of the long axis are distinct (Paramecium caudatum, above, and Stentor roeselii, below).

A cluster of Euplectella aspergillum sponges (Venus flower baskets), showing the apical–basal axes

Term	Meaning	Opposite Term
Superior (Cranial)	Toward the head	Inferior (Caudal)
Anterior (Ventral)	Toward the front	Posterior (Dorsal)
Medial	Toward the midline	Lateral
Proximal	Nearer to the body center	Distal
Superficial	Near the surface	Deep

Frequently Asked Questions

What is the difference between anterior and ventral?

In human anatomy, anterior and ventral both generally refer to the front of the body. However, ventral is more commonly used in embryology and neuroanatomy, while anterior is the standard term for general body surface description.

Why do veterinary terms differ from human anatomical terms?

The difference is primarily due to the neuraxis. Because quadrupeds walk on four legs, their "back" (dorsal) is their top surface, whereas in bipedal humans, the "back" is the posterior surface.

What does contralateral mean in a medical context?

Contralateral refers to the opposite side of the body. A common example is the brain's organization, where the left hemisphere controls the contralateral (right) side of the body.

How are proximal and distal used to describe limbs?

Proximal refers to the part of the limb closest to where it joins the torso (e.g., the shoulder is proximal to the elbow), while distal refers to the part furthest away (e.g., the fingers are distal to the wrist).

What is the meaning of aboral in non-bilaterian organisms?

Aboral is used for organisms that lack a traditional front/back symmetry, such as jellyfish, to describe the side or region that is furthest away from the mouth (oral surface).