Anatomical terms of location
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In human and zoological anatomy (sometimes called zootomy), several terms are used to describe the location of organs and other structures in the body of bilateral animals. These terms, generally derived from Latin, are listed and explained here.
In some cases, the terminology in human anatomy may differ from that in general anatomy, which also applies to other species (where some very different organs occur).
Directions
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 surface or side of the body normally oriented upwards, away from the pull of gravity, 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: in vertebrates, the spine or nerve cord is located on the dorsal side of the organism. A dolphin's dorsal fin is, unsurprisingly, on the dorsal side. A cow's udder is on the ventral side.
On the limbs or other appendages, a point closer to the main body is "proximal"; a point farther away is "distal".
The right and left side (sometimes in Latin: dexter - right, and sinister - left) are always given as viewed from the animal that is described.
Usage in human anatomy
In human anatomy, the body and its parts are always described using the assumption that the subject is standing upright and facing forwards, with the palms directed forwards.Portions of the body which are closer to the head end are "superior" (Latin "upper"); those which are farther away are "inferior" ("lower") -- superior corresponds to cranial ('at the skull'), and inferior to caudal ('at the tail'). Objects near the front are "anterior"; those near the rear are "posterior" -- these correspond respectively to "ventral" and "dorsal".
The terms "anterior" and "posterior" are confusing when referring to most animals, however, and are particularly unsuitable for quadrupeds. In this case, "rostral/cranial" and "caudal" are more appropriate.
- However the word posterior is commonly used (in common slang usage) as a substantive meaning the buttocks or an adjective referring to them, as in 'posterior discipline' (such as spanking)
In the anatomical position, the most superior point on the skull is known as the vertex.
In humans, the position of the forearm with the palm directed anteriorly (or upwards when seated) is known as the supine position. Where the palm faces posteriorly (or downwards when seated), this is the prone position. Turning the hand from prone to supine is called supination; turning the hand from supine to prone is pronation. Pronation results in crossing of the radius with respect to the ulna. To avoid confusion with "medial" and "lateral", different terms are used when describing the sides of the forearm (see below).
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 more distant 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 attached to or associated with an organ, while parietal refers to a structure associated with or attached to the body wall (the chest wall or the abdominal wall). For example, whilst the pleura is a single structure, for convenience the term "visceral pleura" is used to refer to that part attached to the outer surface of the lung, and "parietal pleura" to refer to that part attached to the inside of the chest wall.
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, structures closer to the ulna are ulnar, and structures relating to both bones are referred to as radioulnar. 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".
The terms valgus and varus are used to refer to angulation of the distal part of a limb at a joint. For example, at the elbow joint, in the anatomical position, the forearm and the upper arm do not lie in a straight line, but the forearm is angulated laterally with respect to the upper arm by about 5-10°. The forearm is said to be "in valgus". Angulation at a joint may be normal (as in the elbow) or abnormal.
Planes
General usage
Three basic reference planes are used in zoological anatomy. A sagittal plane divides the body into left and right portions. The midsagittal plane is in the midline, i.e. it would pass through midline structures such as the navel or spine, and all other sagittal planes are parallel to it. A coronal plane divides the body into dorsal and ventral portions. A transverse plane divides the body into cranial and caudal portions.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 front and back, the Y-axis passing left and right, and the Z-axis going up and down.By convention, when displaying axial images, the image is positioned as if the viewer were standing at the feet of a reclining subject, looking towards the head.
- A transverse (also known as axial or horizontal) plane is an X-Y plane, parallel to the ground, which (in humans) separates the superior from the inferior, or put another way, the head from the feet.
- A coronal (also known as frontal) plane is an Y-Z plane, perpendicular to the ground, which (in humans) separates the anterior from the posterior, the front from the back, the ventral from the dorsal.
- A sagittal plane is an X-Z plane, perpendicular to the ground and to the coronal plane, which separates left from right. The midsagittal plane is the specific sagittal plane that is exactly in the middle of the body.
Relative motions
See also
External links
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