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Zootomical terms of location

In zootomy, several terms are used to describe the location of organss and other structures in the body of bilateral animals. These terms are listed and explained here. In some cases, the terminology in human anatomy may differ from that in general anatomy (see below). Some specific details of human anatomy are described under anatomical position.

Table of contents
1 Directions
2 Planes
3 Relative directions
4 Relative Motions
5 See Also:


Anatomical directions and planes shown on a kangaroo.

General usage

Animals typically have one end with a head and mouth, with the opposite end often having the anus and tail. The head end is the cranial end; the tail end is the caudal end. Within the head itself, rostral refers to the direction toward the end of the nose, and caudal is still used to refer to the tail direction.

The side of animals with the spine or nerve chord is the dorsal side; the opposite side, typically the one closest to the ground when walking on all legs, swimming or flying, is the ventral side. For example: a cow's udder is on the ventral side. A dolphin's dorsal fin is, unsurprisingly, on the dorsal side.

The right and left side (sometimes in Latin: dexter - right, and sinister - left) are given as viewed from the animal that is described.

Usage in human anatomy

One's torso is divided from the waist, by the transverse plane; one's right-side is divided from the left-side, by the midsagittal plane; and one's rear is divided from the front, by the frontal plane.

Portions of the body which are clsoer to the head, are "superior" ("upper"); those which are farther away, are "inferior" ("lower") -- superior corresponds to cranial, and inferior to caudal. Objects near the front are "anterior"; those near the rear are "posterior" -- these correspond respecitvely to "ventral" and "dorsal". On the limbs, an object closer to the main body is "proximal"; an object farther away is "distal". Such terms are discussed further at: terms for anatomical location.

The terms anterior and posterior should not be used when refering to most animals however, and are particularly incorrect for quadrupeds.


Usage in human anatomy

Sometimes the orientation of certain planes need to be distinguished, for instance in
medical imaging techniques such as CT scans, MRI scans or PET scans. One imagines a human in anatomical position (standing, arms hanging down with palms to the front) and an X-Y-Z coordinate system with the X-Y plane parallel to the ground, the X-axis going from left to right, the Y-axis passing from front to back, and the Z-axis going up and down.

Relative directions

Structures near the midline are called medial and those near the sides of animals are called lateral. Therefore, medial structures are closer to the midsagittal plane, lateral structures are further from the midsagittal plane. Structures in the midline of the body are median. For example, your cheeks are lateral to your nose and the tip of the nose is in the median line.

Structures that are close to the center of the body are proximal or central, while ones far removed are distal or peripheral. For example, the hands are at the distal end of the arms, while the shoulders are at the proximal ends. These terms can also be used relatively to organs, for example the proximal end of the urethra is attached to the bladder.

Structures on or close to the body´s surface are superficial and those further inside are profound or deep.

When speaking of inner organs, visceral means close to or attached to the organ, while parietal is more distant. For example, the visceral pleura is attached to the lung and the parietal pleura is attached to the chest wall.

Relative directions in the limbs

In the limbs, the terms cranial and caudal are used in the region proximal to the carpus (the "wrist", in the forelimb) and the tarsus (the "ankle" in the hindlimb). Distal to the carpal joint, the forward direction in animals and the top of the palm region in humans is referred to as dorsal, while the rearward direction is referred to as palmar. Distal to the tarsal joint, the forward direction in animals, and the top of the foot in humans, is referred to as dorsal, while the rearward direction is referred to as plantar. The sides of the forearm are named after its bones: Structures closer to the radius are radial, and structures closer to the ulna are ulnar. Similarly, in the lower leg, structures near the tibia (shinbone) are tibial and structures near the fibula are fibular (or peroneal).

Relative Motions

Flexion means approximating adjacent parts of the body (usually at a joint) and extension means separating them. For example, the legs are are flexed at the knee joints when sitting down, and extended when standing up. Generally, flexion produces an acute angle between adjacent parts, with its vertex at the joint, and extension produces an obtuse angle. One exception to this rule is in the ankle joint where moving the foot such that the toes move upwards is dorsiflexion and moving the foot such that the toes move downwards is plantar flexion.

Adduction means moving a part of the body toward or past its median line or toward the long axis of a limb. Abduction means moving a part of the body away from its median line or away from the long axis of a limb. For example, adducting the thighs brings the legs together, and abducting the thighs spreads the legs apart. Similarly, adducting the fingers brings them into contact with one another, and abducting the fingers spreads them apart.

Rotation means moving a part about its long axis, for example, in turning the neck. Supination means rotation of the forearm such that the palm of the hand faces forward or upward, and pronation means rotation of the forearm such that the palm of the hand faces backward or downward; the forearm with the hand is supinated or pronated at the elbow. Similar movements may be accomplished at the ankle, where supination results in the foot tipping inward relative to its long axis, and pronation results in the foot tipping outward; overpronation may contribute to the condition flatfoot.

An anterograde motion is in the normal direction of flow, while retrograde means reversed flow. For example, passage of food from the mouth to the stomach is in an anterograde direction, and gastric reflux is in a retrograde direction.

See Also:

Nomina Anatomica Veterinaria