Anatomical terms of location: Encyclopedia II - Anatomical terms of location - Relative directions

Anatomical terms of location - 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. Ipsilateral means on the same side, contralateral means on the other side and bilateral means on both sides.

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 closer to the body´s surface are superficial (or external) and those further inside are profound or deep (or internal).

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.

Anatomical terms of location - Relative directions in the limbs

In the limbs of most animals, the terms cranial and caudal are used in the regions proximal to the carpus (the wrist, in the forelimb) and the tarsus (the ankle in the hindlimb). Objects and surfaces closer to or facing towards the head are cranial; those facing away or further from the head are caudal. This usage is not common in human anatomy, however.

Distal to the carpal joint, the term dorsal replaces cranial and palmar replaces caudal. Similarly, distal to the tarsal joint the term dorsal replaces cranial and plantar replaces caudal. For example, the top of a dog's paw is its dorsal surface; the underside, either the palmar (on the forelimb) or the plantar (on the hindlimb) surface.

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).

Volar, a term which refers to both the palm and the sole, is sometimes used as a synonym for "palmar".

Adapted from the Wikipedia article "Relative directions", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki