Gross Anatomy: Directional Terms

Directional Terms

An understanding of the following planes, positions, and directions relative to the animal body or its parts is necessary to follow the procedures for dissection.

PLANE

A surface, real or imaginary, along which any two points can be connected by a straight line.

Median Plane

Divides the head, body, or limb longitudinally into equal right and left halves.

Sagittal Plane

Passes through the head, body, or limb parallel to the median plane.

Transverse (Horizontal) Plane

Cuts across the head, body, or limb at a right angle to its long axis or across the long axis of an organ or a part.

Dorsal (Frontal) Plane

Runs at right angles to the median and transverse planes and thus divides the body or head into dorsal and ventral portions

DORSAL

Toward or relatively near the upper surface (as opposed to the supporting surface) of the head, body, and tail.

VENTRAL

Toward or relatively near the supporting surface and the corresponding surface of the head, neck, thorax, and tail. This term is never used for the limbs.

MEDIAL

Toward or relatively near the median plane.

LATERAL

Away from or relatively farther from the median plane

CRANIAL

Toward or relatively near the head; on the limbs it applies proximal to the carpus and tarsus. In reference to the head, it is replaced by the term rostral.

ROSTRAL

Toward or relatively near the nose; applies to the head only.

CAUDAL

Toward or relatively near the tail; on the limbs it applies proximal to the carpus and tarsus. Also used in reference to the head.

INTERNAL or INNER

Close to, or in the direction of, the center of an organ, body cavity, or structure.

EXTERNAL or OUTER

Away from the center of an organ or structure

Superficial

Relatively near the surface of the body or the surface of a solid organ.

DEEP

Relatively near the center of the body or the center of a solid organ.

PROXIMAL

Relatively near the main mass or origin; in the limbs and tail, the attached end of that structure.

DISTAL

Away from the main mass or origin; in the limbs and tail, the free end of that structure.

RADIAL

On that side of the forearm (antebrachium) in which the radius is located.

ULNAR

On that side of the forearm in which the ulna is located.

TIBIAL and FIBULAR

On the corresponding sides of the leg (crus), the tibial side being medial and the fibular side being lateral.

PALMAR

The aspect of the forepaw on which the pads are located—the surface that contacts the ground in the standing animal—and the corresponding surface of the metacarpus and carpus.

PLANTAR

The aspect of the hindpaw on which the pads are located—the surface that contacts the ground in the standing animal—and the corresponding surface of the metatarsus and tarsus. “The opposite surface of both forepaw and hindpaw is known as the dorsal surface.”

AXIS

The central line of the body or any of its parts.

AXIAL, ABAXIAL

Of, pertaining to, or relative to the axis. In reference to the digits, the functional axis of the limb passes between the third and fourth digits. The axial surface of the digit faces the axis, and the abaxial surface faces away from the axis.

FLEXION

The movement of one bone in relation to another in such a manner that the angle formed at their joint is reduced

EXTENSION

The movement of one bone upon another such that the angle formed at their joint increases.

ABDUCTION

The movement of a part away from the median plane.

ADDUCTION

The movement of a part toward the median plane.

CIRCUMDUCTION

The movement of a part when outlining the surface of a cone (e.g., the thoracic limb extended drawing a circle).

ROTATION

The movement of a part around its long axis (e.g., the action of the radius when using a screwdriver). The direction of rotation of a limb or segment of a limb on its long axis is designated by the direction of movement of its cranial or dorsal surface (e.g., in medial rotation of the arm, the crest of the greater tubercle is turned medially).

SUPINATION

Lateral rotation of the appendage so that the palmar or plantar surface of the paw faces medially.

PRONATION

Medial rotation of the appendage from the supine position so that the palmar or plantar surface will face the substrate.

Brachium

for the arm (between shoulder and elbow)

Antebrachium

for the forearm (between elbow and carpus)

Thigh

for the pelvic limb (between the hip and stifle)

Crus

for the leg (between stifle and tarsus)