Anatomical terms of location

and whether an animal is a vertebrate or invertebrate. Standard anatomical terms of location have been developed, usually based on Latin and Greek words, to enable all biological and medical scientists, veterinarians, medical 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, Terminologia Neuroanatomica, and Terminologia Embryologica), with Nomina Anatomica Veterinaria and Nomina Embryologica Veterinaria used for animal anatomy. Different terms are used for those vertebrates that are bipedal and those that are quadrupedal. 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, even when its appendages are in another position. This helps to avoid confusion in terminology when referring to the same animal in different postures. In humans, this refers to the body in a standing position with arms at the side and palms facing forward. For a fish this is belly down with neutral appendages. Planes Anatomical terms describe structures with relation to three main anatomical planes. The three main plane orientations are: • The sagittal planes, also called the parasagittal planes or paramedian planes, are planes that divide the body into left and right. • The coronal plane or frontal plane divides the body into front and back parts. Axes vertebrates The three axes of a vertebrate, are formed in embryonic development before and during the gastrulation stage. Distinct ends of the embryo are chosen, and the axis is named according to those directions. The three main axes of a bilaterally symmetrical animal that intersect at right angles, are the left-right, the craniocaudal, and the anteroposterior axes. An organism that is round, or asymmetrical may have different axes. ==Main terms==

Superior and inferior In the standard human anatomical position, superior () or cranial, describes something that is nearer to the head, and inferior () or caudal describes what is below, and nearer to the feet. In veterinary anatomy, the terms superior and inferior are not used except to describe the eye, eyelids, lips and inner ear, using instead dorsal and ventral. For example, for many fish the gill openings are posterior to the eyes and anterior to the tail. In veterinary anatomy, these terms are reserved for some structures of the head, instead using cranial and caudal throughout the rest of the body. The terms are used in other contexts, for example in dorsal and ventral gun turrets on a bomber aircraft. Medial and lateral These terms describe how close something is to the median plane. Varus () and valgus ( ) are terms used to describe angulation or bowing of a bone or joint within the coronal plane, where the distal portion deviates towards (varus) or away from (valgus) the midline. Proximal and distal The terms proximal () and distal () 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. The main mass is taken as the center, the chest, or the heart. 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. Rostral, cranial, and caudal , the terms rostral and caudal are adapted to the curved neuraxis of Hominidae, rostrocaudal meaning the region on C shape connecting rostral and caudal regions. Specific terms exist to describe how close or far something is to the head or tail of an animal. To describe how close to the head of an animal something is, three distinct terms are used: • Rostral () describes something situated toward the oral or nasal region, or in the case of the brain, toward the tip of the frontal lobe. For example, in horses, the eyes are caudal to the nose and rostral to the back of the head. For example, the great vessels run centrally through the body; many smaller vessels branch from these. Peripheral (, originally from Ancient Greek) describes something that is situated nearer to the body's surface, such as a peripheral nerve. Superficial and deep These terms refer to the distance of a structure from the surface. Deep () describes something further away from the surface of the organism. The term can also describe the direction and location of something that enters or courses through the body such as the anterolateral system in the spinal cord, and the anterolateral central arteries. Another term anteromedial is used for example in the anteromedial central arteries. In the more internal brain and spinal cord of the central nervous system the terms dorsal and ventral and their combinations are often used in place of anterior and posterior. In these organs numerous references need to be used, and in the brain for example the prefrontal cortex has the divisions of the dorsomedial prefrontal cortex, and the dorsolateral prefrontal cortex. And the dorsomedial region has subcompartments that make use of other terms such as the anterior cingulate cortex, and infralimbic cortex. Structures such as the anterior cingulate cortex may be divided anatomically based on cognitive (dorsal), and emotional (ventral) components. Proximodistal is the axis of an appendage such as an arm or a leg, taken from its tip at the distal part to where it joins the body at the proximal part. Combined terms were once generally hyphenated, but typically the hyphen is omitted. Modifiers 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- () is used to indicate something that is beneath, or something that is subordinate to or lesser than. For example, "distad" means "in the distal direction," as in "arterial blood flows distad/distally." Further examples may include cephalad (towards the cephalic end), orad, craniad, and proximad. The terms "proximally" and "distally" are in more common use in human and veterinary anatomic textbooks, while "proximad" and "distad," are used commonly in insect anatomy. ==Other terms and special cases==

Anatomical landmarks The location of anatomical structures can also be described in relation to different anatomical landmarks used in anatomy, surface anatomy, surgery, and radiology. Structures may be described as being at the level of a specific vertebra, depending on the section of the vertebral column the structure is at. For example, the terms "distal" and "proximal" (or "mesial") are used for surfaces of individual teeth relative to the midpoint of the dental arch, and "medial" and "lateral" are used in the standard sense relative to the median plane. Terms used to describe structures include "buccal" () and "palatal" () referring to structures close to the cheek and hard palate respectively. But palmar is used exclusively for the palm of the hand, and plantar is used exclusively for the sole of the foot. Similarly, in the limbs for clarity, the sides are named after the bones. In the forearm, 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, such as the distal radioulnar joint. Similarly, in the lower leg, structures near the tibia (shinbone) are tibial and structures near the fibula are fibular (or peroneal). Rotational direction Anteversion and retroversion are complementary terms describing an anatomical structure that is rotated forwards (towards the front of the body) or backwards (towards the back of the body), relative to some other position. They are particularly used to describe the curvature of the uterus. • Anteversion () describes an anatomical structure being tilted further forward than normal, whether pathologically or incidentally. • Retroversion () describes an anatomical structure tilted back away from something. Two related terms, "abaxial" and "adaxial", refer to locations away from and toward the central axis of an organism, respectively • Luminal (): on the—hollow—inside of an organ's lumen (body cavity or tubular structure); adluminal is towards, abluminal is away from the lumen. Opposite to outermost (the adventitia, serosa, or the cavity's wall). • Terminal () at the extremity of a usually projecting structure; forming the end of a structure such as an axon terminal. • Visceral (): associated with the innermost layer of an organ within the body. For example, the visceral pleura covering the lungs, contrasted with the parietal pleura lining the thoracic cavity. • Parietal (): pertaining to the wall of a body cavity as the parietal pleura lining the thoracic cavity, contrasted with visceral pleura. • Aboral (away from oral) is used to denote a location in an organism that is further from the mouth. ==Other animals==

Different terms are used because of different body plans in animals, whether animals stand on two or four legs, and whether an animal is symmetrical or asymmetrical. For example, as humans are bilaterally symmetrical, anatomical descriptions usually use the same terms as those for other vertebrates. The term "rostral" used to refer to the beak or nose in some animals is used less frequently in humans, with the exception of parts of the brain; Invertebrates have a large variety of body shapes that can present a problem when trying to apply standard directional terms. Depending on the organism, some terms are taken by analogy from vertebrate anatomy, and appropriate novel terms are applied as needed. Some such borrowed terms are widely applicable in most invertebrates; for example proximal, meaning "near" refers to the part of an appendage nearest to where it joins the body, and distal, meaning "standing away from" is used for the part furthest from the point of attachment. In all cases, the usage of terms is dependent on the body plan of the organism. Direcoes anatomicas.svg|Anatomical terms of location in a dog Anatomical-directions-kangaroo.svg|Anatomical terms of location in a kangaroo Anatomical Directions and Axes.JPG|Anatomical terms of location in most fish Horse Axes.JPG|Anatomical terms of location in a horse File:Pseudopleuronectes americanus.jpg|Flatfish are asymmetric, with both eyes lying on the same side of the head. Non-bilaterian organisms . (a) An organism with an asymmetrical, amoeboid body plan (Amoeba proteus an amoeba). (b) An organism with a spherical amoeboid body plan (Actinophrys sol a heliozoan). In non-bilaterian organisms with a changeable shape, such as amoeboid organisms, most directional terms are meaningless, since the shape of the organism is not constant and no distinct axes are fixed. Similarly, in radially symmetrical organisms, there is nothing to distinguish one line through the centre of the organism from any other. An indefinite number of triads of mutually perpendicular axes could be defined, but any such choice of axes would be useless, as nothing would distinguish a chosen triad from any others. In such organisms, only terms such as superficial and deep, or sometimes proximal and distal, are usefully descriptive. Elongated organisms '', a diatom with a fixed elongated shape In organisms that maintain a constant shape and have one dimension longer than the other, at least two directional terms can be used. The long or longitudinal axis is defined by points at the opposite ends of the organism. Similarly, a perpendicular transverse axis can be defined by points on opposite sides of the organism. There is typically no basis for the definition of a third axis. Usually such organisms are planktonic (free-swimming) protists, and are nearly always viewed on microscope slides, where they appear essentially two-dimensional. In some cases a third axis can be defined, particularly where a non-terminal cytostome or other unique structure is present. , above, and Stentor roeselii'', below). Some elongated protists have distinctive ends of the body. In such organisms, the end with a mouth (or equivalent structure, such as the cytostome in Paramecium or Stentor), or the end that usually points in the direction of the organism's locomotion (such as the end with the flagellum in Euglena), is normally designated as the anterior end. The opposite end then becomes the posterior end. , showing the apical–basal axes Organisms that are attached to a substrate, such as sponges and animal-like protists also have distinctive ends. The part of the organism attached to the substrate is usually referred to as the basal end (), whereas the end furthest from the attachment is referred to as the apical end (). Radially symmetrical organisms Radially symmetrical organisms include those in the group Radiata primarily Cnidarians (jellyfish, sea anemones and corals, and the comb jellies). Adult echinoderms, such as starfish, sea urchins, sea cucumbers and others are also included, since they have a pentamerous symmetry having five discrete symmetric parts arranged around a central axis. Echinoderm larvae are not included, since they are bilaterally symmetrical. Comb jellies have a biradial symmetry about only two planes, a tentacular plane, and a pharyngeal plane. Image:Radiate Radial Axes.JPG|Aurelia aurita, another species of jellyfish, showing multiple radial and medio-peripheral axes File:Porania_pulvillus.jpg|The sea star Porania pulvillus, aboral and oral surfaces Spiders Special terms are used for spiders. Two such terms are useful in describing views of the legs and pedipalps of spiders, and other arachnids. Prolateral refers to the surface of a leg that is closest to the anterior end of an arachnid's body. Retrolateral refers to the surface of a leg that is closest to the posterior end of an arachnid's body. Most spiders have eight eyes in four pairs. All the eyes are on the carapace of the prosoma, and their sizes, shapes and locations are characteristic of various spider families and other taxa. Usually, the eyes are arranged in two roughly parallel, horizontal and symmetrical rows of eyes. Eyes are labelled according to their position as anterior and posterior lateral eyes (ALE) and (PLE); and anterior and posterior median eyes (AME) and (PME). File:Palystes superciliosus male anterior 2012 03 04 3452.JPG|Aspects of spider anatomy. This aspect shows the mainly prolateral surface of the anterior femora, plus the typical horizontal eye pattern of the Sparassidae. File:Hogna species female Lycosidae showing eye pattern EOS 027s.jpg|Typical arrangement of eyes in the Lycosidae, with PME being the largest File:Salticidae Male Anterior annotated.jpg|In the Salticidae the AME are the largest. ==See also==