anatomical terms of location anatomical terms of location standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. the terms, typically derived from latin or greek roots, describe something in its standard anatomical position. this position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. as part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axes. this article is part of a series onanatomical terminology bonelocationmicroanatomymotionmuscleneuroanatomy the meaning of terms that are used can change depending on whether an organism is bipedal or quadrupedal. additionally, for some animals such as invertebrates, some terms may not have any meaning at all; for example, an animal that is radially symmetrical will have no anterior surface, but can still have a description that a part is close to the middle ("proximal") or further from the middle ("distal"). international organisations have determined vocabularies that are often used as standard vocabularies for subdisciplines of anatomy, for example, terminologia anatomica for humans, and nomina anatomica veterinaria for animals. these allow parties that use anatomical terms, such as anatomists, veterinarians, and medical doctors to have a standard set of terms to communicate clearly the position of a structure. introduction 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 and zoological terms of location have been developed, usually based on latin and greek words, to enable all biological and medical scientists, veterinarians, doctors and anatomists to precisely delineate and communicate information about animal bodies and their organs, even though the meaning of some of the terms often is context-sensitive. much of this information has been standardised in internationally agreed vocabularies for humans (terminologia anatomica) and animals (nomina anatomica veterinaria). for humans, one type of vertebrate, and other animals that stand on two feet (bipeds), terms that are used are different from those that stand on four (quadrupeds). one reason is that humans have a different neuraxis and another is that unlike animals that rest on four limbs, humans are considered when describing anatomy as being in the standard anatomical position, which is standing up with arms outstretched. thus, what is on "top" of a human is the head, whereas the "top" of a dog may be its back, and the "top" of a flounder could refer to either its left or its right side. unique terms are used to describe animals without a backbone (invertebrates), because of their wide variety of shapes and symmetry. standard anatomical position main article: standard anatomical position a male and female human in the standard anatomical position because animals can change orientation with respect to their environment, and because appendages like limbs and tentacles can change position with respect to the main body, terms to describe position need to refer to an animal when it is in its standard anatomical position. this means descriptions as if the organism is in its standard anatomical position, even when the organism in question has appendages in another position. this helps avoid confusion in terminology when referring to the same organism in different postures. in humans, this refers to the body in a standing position with arms at the side and palms facing forward, with thumbs out and to the sides. combined terms anatomical terms can be combined to be more specific. this is a dorsolateral view of the frog mantophryne insignis. many anatomical terms can be combined, either to indicate a position in two axes simultaneously or to indicate the direction of a movement relative to the body. for example, "anterolateral" indicates a position that is both anterior and lateral to the body axis (such as the bulk of the pectoralis major muscle). in radiology, an x-ray image may be said to be "anteroposterior", indicating that the beam of x-rays passes from their source to patient's anterior body wall through the body to exit through posterior body wall. combined terms were once generally hyphenated, but the modern tendency is to omit the hyphen. planes main article: anatomical plane anatomical planes in a human anatomical terms describe structures with relation to four main anatomical planes: the median plane, which divides the body into left and right. this passes through the head, spinal cord, navel, and, in many animals, the tail. the sagittal planes, which are parallel to the median plane. the frontal plane, also called the coronal plane, which divides the body into front and back. the horizontal plane, also known as the transverse plane, which is perpendicular to the other two planes. in a human, this plane is parallel to the ground; in a quadruped, this divides the animal into anterior and posterior sections. axes organisms where the ends of the long axis are distinct. (paramecium caudatum, above, and stentor roeselii, below.) the axes of the body are lines drawn about which an organism is roughly symmetrical. to do this, distinct ends of an organism are chosen, and the axis is named according to those directions. an organism that is symmetrical on both sides has three main axes that intersect at right angles. an organism that is round or not symmetrical may have different axes. example axes are: the anteroposterior axis the cephalocaudal axis the dorsoventral axis examples of axes in specific animals are shown below. anatomical axes in a human, similar for other orthograde bipedal vertebrates anatomical axes and directions in a fish spheroid or near-spheroid organs such as testes may be measured by "long" and "short" axis. modifiers 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. several terms are commonly seen and used as prefixes: sub- (from latin sub 'preposition beneath, close to, nearly etc') is used to indicate something that is beneath, or something that is subordinate to or lesser than. for example, subcutaneous means beneath the skin, and "subglobular" may mean smaller than a globule hypo- (from ancient greek ὑπό 'under') is used to indicate something that is beneath. for example, the hypoglossal nerve supplies the muscles beneath the tongue. infra- (from latin infra 'under') is used to indicate something that is within or below. for example, the infraorbital nerve runs within the orbit. inter- (from latin inter 'between') is used to indicate something that is between. for example, the intercostal muscles run between the ribs. super- or supra- (from latin super, supra 'above, on top of') is used to indicate something that is above something else. for example, the supraorbital ridges are above the eyes. other terms are used as suffixes, added to the end of words: -ad (from latin ad 'towards') and ab- (from latin ab) are used to indicate that something is towards (-ad) or away from (-ab) something else. for example, "distad" means "in the distal direction", and "distad of the femur" means "beyond the femur in the distal direction". further examples may include cephalad (towards the cephalic end), craniad, and proximad. main terms superior and inferior superior (from latin super 'above') describes what is above something and inferior (from latin inferus 'below') describes what is below it. for example, in the anatomical position, the most superior part of the human body is the head and the most inferior is the feet. as a second example, in humans, the neck is superior to the chest but inferior to the head. anterior and posterior anterior (from latin ante 'before') describes what is in front, and posterior (from latin post 'after') describes what is to the back of something. for example, for a dog the nose is anterior to the eyes and the tail is considered the most posterior part; for many fish the gill openings are posterior to the eyes but anterior to the tail. medial and lateral these terms describe how close something is to the midline, or the medial plane. lateral (from latin lateralis 'to the side') describes something to the sides of an animal, as in "left lateral" and "right lateral". medial (from latin medius 'middle') describes structures close to the midline, or closer to the midline than another structure. for example, in a human, the arms are lateral to the torso. the genitals are medial to the legs. the terms "left" and "right" are sometimes used, or their latin alternatives (latin: dexter, lit. 'right'; latin: sinister, lit. 'left'). however, as left and right sides are mirror images, using these words is somewhat confusing, as structures are duplicated on both sides. for example, it is very confusing to say the dorsal fin of a fish is "right of" the left pectoral fin, but is "left of" the right eye, but much easier and clearer to say "the dorsal fin is medial to the pectoral fins". terms derived from lateral include: contralateral (from latin contra 'against'): on the side opposite to another structure. for example, the right arm and leg are controlled by the left, contralateral, side of the brain. ipsilateral (from latin ipse 'same'): on the same side as another structure. for example, the left arm is ipsilateral to the left leg. bilateral (from latin bis 'twice'): on both sides of the body. for example, bilateral orchiectomy means removal of testes on both sides of the body. unilateral (from latin unus 'one'): on one side of the body. for example, a stroke can result in unilateral weakness, meaning weakness on one side of the body. varus (from latin 'bow-legged') and valgus (from latin 'knock-kneed' ) are terms used to describe a state in which a part further away is abnormally placed towards (varus) or away from (valgus) the midline. proximal and distal "proximal" and "distal" redirect here. for the linguistic terms, see demonstrative § distal and proximal demonstratives. for the dental terms, see glossary of dentistry. anatomical directional reference the terms proximal (from latin proximus 'nearest') and distal (from latin distare 'to stand away from') are used to describe parts of a feature that are close to or distant from the main mass of the body, respectively. thus the upper arm in humans is proximal and the hand is distal. "proximal and distal" are frequently used when describing appendages, such as fins, tentacles, and limbs. although the direction indicated by "proximal" and "distal" is always respectively towards or away from the point of attachment, a given structure can be either proximal or distal in relation to another point of reference. thus the elbow is distal to a wound on the upper arm, but proximal to a wound on the lower arm. this terminology is also employed in molecular biology and therefore by extension is also used in chemistry, specifically referring to the atomic loci of molecules from the overall moiety of a given compound. central and peripheral central and peripheral refer to the distance towards and away from the centre of something. that might be an organ, a region in the body, or an anatomical structure. for example, the central nervous system and the peripheral nervous systems. central (from latin centralis) describes something close to the centre. for example, the great vessels run centrally through the body; many smaller vessels branch from these. peripheral (from latin peripheria, originally from ancient greek) describes something further away from the centre of something. for example, the arm is peripheral to the body. superficial and deep these terms refer to the distance of a structure from the surface. deep (from old english) describes something further away from the surface of the organism. for example, the external oblique muscle of the abdomen is deep to the skin. "deep" is one of the few anatomical terms of location derived from old english rather than latin – the anglicised latin term would have been "profound" (from latin profundus 'due to depth'). superficial (from latin superficies 'surface') describes something near the outer surface of the organism. for example, in skin, the epidermis is superficial to the subcutis. dorsal and ventral these two terms, used in anatomy and embryology, describe something at the back (dorsal) or front/belly (ventral) of an organism. the dorsal