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Standard anatomical terms of location are used to unambiguously describe the
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual conti ...

anatomy
of
animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, ...

animal
s, including
human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use of culture, language and tools. They are the only Extant taxon, ...

human
s. The terms, typically derived from
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became the ...

Latin
or
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
roots, describe something in its
standard anatomical position The standard anatomical position, or standard anatomical model, is the scientifically agreed upon reference position for anatomical location terms. Standard anatomical positions are used to standardise the position of appendages An appendage ( ...
. 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 plane An anatomical plane is a hypothetical plane Plane or planes may refer to: * Airplane or aeroplane or informally plane, a powered, fixed-wing aircraft Arts, entertainment and media *Plane (Dungeons & Dragons), Plane (''Dungeons & Dragons''), ...
s and anatomical axes. The meaning of terms that are used can change depending on whether an organism is
bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biologica ...
or
quadrupedal The zebra is a quadruped. Quadrupedalism is a form of terrestrial locomotion where a tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amph ...
. Additionally, for some animals such as
invertebrate Invertebrates are animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular resp ...
s, 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 ''Terminologia Anatomica'' (''TA'') is the international standard on human anatomic terminology. It was developed by the Federative Committee on Anatomical Terminology The Federative International Committee for Anatomical Terminology (FICAT) is a ...
for humans, and
Nomina Anatomica Veterinaria The ''Nomina Anatomica Veterinaria'' (often abbreviated as ''NAV'') is an standardized Standardization or standardisation is the process of implementing and developing technical standard A technical standard is an established norm or requirem ...
for animals. These allow parties that use anatomical terms, such as
anatomist Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mo ...
s,
veterinarian A veterinarian (vet), also known as a veterinary surgeon or veterinary physician, is a medical professional who practices veterinary medicine by treating diseases, disorders, managing reproductive health and injuries in non-human animal ...
s, and
medical doctor A physician (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American Eng ...

medical doctor
s to have a standard set of terms to communicate clearly the position of a structure.


Introduction

Standard
anatomical Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mo ...

anatomical
and
zoological Zoology ()The pronunciation of zoology as is typically regarded as nonstandard, though it is not uncommon. is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical s ...
terms of location have been developed, usually based on
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became the ...

Latin
and
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
words, to enable all biological and medical scientists,
veterinarian A veterinarian (vet), also known as a veterinary surgeon or veterinary physician, is a medical professional who practices veterinary medicine by treating diseases, disorders, managing reproductive health and injuries in non-human animal ...
s,
doctors Doctor or The Doctor may refer to: Personal titles * Doctor (title), the holder of an accredited academic degree * A medical practitioner, including: ** Physician ** Surgeon *Other roles ** Doctor of the Church, a title given to those with g ...

doctors
and
anatomist Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mo ...
s 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 Anatomica'' (''TA'') is the international standard on human anatomic terminology. It was developed by the Federative Committee on Anatomical Terminology The Federative International Committee for Anatomical Terminology (FICAT) is a ...
) and animals (
Nomina Anatomica Veterinaria The ''Nomina Anatomica Veterinaria'' (often abbreviated as ''NAV'') is an standardized Standardization or standardisation is the process of implementing and developing technical standard A technical standard is an established norm or requirem ...
). For humans, one type of vertebrate, and other animals that stand on two feet (
bipeds Bipedalism is a form of terrestrial locomotion – an erect-stanced unguligrade Ungulates (pronounced ) are members of a diverse clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, i ...
), terms that are used are different from those that stand on four (
quadrupeds The zebra is a quadruped. Quadrupedalism is a form of terrestrial locomotion where a tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amph ...
). One reason is that humans have a different
neuraxis The neuraxis or sometimes neuroaxis is the axis of the central nervous system The central nervous system (CNS) is the part of the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an animal ...
and another is that unlike animals that rest on four limbs, humans are considered when describing anatomy as being in the
standard anatomical position The standard anatomical position, or standard anatomical model, is the scientifically agreed upon reference position for anatomical location terms. Standard anatomical positions are used to standardise the position of appendages An appendage ( ...
, which is standing up with arms outstretched. Thus, what is on "top" of a human is the
head Head Sport GmbH is an American-Austrian manufacturing company headquartered in Kennelbach. It owns the American tennis racket brand Head. Head GmbH is a group that includes several previously independent companies, including the original "Head ...

head
, whereas the "top" of a dog may be its back, and the "top" of a
flounder Flounders are a group of flatfish species. They are demersal fish, found at the bottom of oceans around the world; some species will also enter estuary, estuaries. Taxonomy The name "flounder" is used for several only distantly related specie ...
could refer to either its left or its right side. Unique terms are used to describe animals without a backbone (
invertebrate Invertebrates are animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular resp ...
s), because of their wide variety of shapes and symmetry.


Standard anatomical position

Because
animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, ...

animal
s can change orientation with respect to their environment, and because
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are co ...
s like limbs and
tentacle with 2 tentacles and 8 arms In zoology Zoology ()The pronunciation of zoology as is typically regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the anatomy, structure, emb ...

tentacle
s 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 The standard anatomical position, or standard anatomical model, is the scientifically agreed upon reference position for anatomical location terms. Standard anatomical positions are used to standardise the position of appendages An appendage ( ...
. 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

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 The pectoralis major () is a thick, fan-shaped or triangular convergent muscle, situated at the chest of the human body. It makes up the bulk of the chest Skeletal muscle, muscles and lies under the breast. Beneath the pectoralis major is the pect ...

pectoralis major
muscle). In
radiology Radiology is the medical discipline that uses medical imaging to diagnose and treat diseases within the bodies of animals and humans. A variety of imaging techniques such as X-ray radiography, ultrasound, x-ray computed tomography, computed to ...

radiology
, an
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motio ...

X-ray
image may be said to be "anteroposterior", indicating that the beam of X-rays passes from their source to patient's
anterior Standard anatomical terms of location deal unambiguously with the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient ...
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

Anatomical terms describe structures with relation to four main
anatomical plane An anatomical plane is a hypothetical plane Plane or planes may refer to: * Airplane or aeroplane or informally plane, a powered, fixed-wing aircraft Arts, entertainment and media *Plane (Dungeons & Dragons), Plane (''Dungeons & Dragons''), ...
s: # The
median plane The median plane also called a mid-sagittal plane is used to describe the sagittal plane In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology ...
, which divides the body into left and right. This passes through the
head Head Sport GmbH is an American-Austrian manufacturing company headquartered in Kennelbach. It owns the American tennis racket brand Head. Head GmbH is a group that includes several previously independent companies, including the original "Head ...

head
,
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord, which co ...

spinal cord
,
navel The navel (clinically known as the umbilicus, commonly known as the belly button) is a protruding, flat, or hollowed area on the abdomen The abdomen (colloquially called the belly, tummy, midriff or stomach) is the part of the body between th ...

navel
, and, in many animals, the
tail The tail is the section at the rear end of certain kinds of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotrop ...
. # The
sagittal plane In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...

sagittal plane
s, which are to the median plane. # The frontal plane, also called the
coronal plane A coronal plane (also known as the frontal plane) is any vertical plane that divides the body into ventral and dorsal (belly and back) sections. It is one of the three main planes of the body used to describe the location of body parts in relatio ...
, which divides the body into front and back. # The horizontal plane, also known as the
transverse plane The transverse plane or axial plane (also called the horizontal plane or transaxial plane) is an imaginary plane that divides the body into superior and inferior parts. It is perpendicular to the coronal plane and sagittal plane In anatomy, the ...
, 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

'', 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 angle In geometry and trigonometry, a right angle is an angle of exactly 90 Degree (angle), degrees or π/2 radians corresponding to a quarter turn (geometry), turn. If a Line (mathematics)#Ray, ray is placed so that its endpoint is on a line and the ...

right angle
s. 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.svg, Anatomical axes in a human, similar for other orthograde bipedal vertebrates Anatomical Directions and Axes.JPG, Anatomical axes and directions in a
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

fish
Long and short axis.png,
Spheroid A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric In mathematics, a quadric or quadric surface (quadric hypersurface in higher dimensions), is a generalization of conic sections (ellipse In math ...

Spheroid
or near-spheroid organs such as
testes Testicle or testis (plural testes) is the male reproductive gland or gonad in all animals, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primaril ...

testes
may be measured by "long" and "short" axis.


Modifiers

Several terms are commonly seen and used as
prefix A prefix is an affix which is placed before the Word stem, stem of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix ''un-'' is added to the word ''happy'', it creates the word ''unhappy'' ...
es: * Sub- () 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 * Hypo- () is used to indicate something that is beneath. For example, the
hypoglossal nerve The hypoglossal nerve is the twelfth cranial nerve, and innervates all the extrinsic and intrinsic muscles of the tongue, except for the palatoglossus which is innervated by the vagus nerve The vagus nerve, historically cited as the pneumog ...
supplies the muscles beneath the tongue. * Infra- () is used to indicate something that is within or below. For example, the
infraorbital nerve The infraorbital nerve is a branch of the maxillary nerve, itself a branch of the trigeminal nerve The trigeminal nerve (the fifth cranial nerve, or simply CN V) is a nerve responsible for sensation in the face and motor functions such as bitin ...
runs within the
orbit In celestial mechanics, an orbit is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificial satellite around an object or pos ...
. * Inter- () is used to indicate something that is between. For example, the
intercostal muscle Intercostal muscles are many different muscle groups of muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains o ...
s run between the
rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest ...
s. * Super-'' or ''Supra- () is used to indicate something that is above something else. For example, the
supraorbital ridge The brow ridge, or supraorbital ridge known as superciliary arch in medicine, refers to a bony ridge located above the eye sockets of all primates. In '' Homo sapiens sapiens'' (modern humans) the eyebrows are located on their lower margin. Stru ...
s are above the
eye Eyes are organs of the visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which ...

eye
s. Other terms are used as
suffix In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. The traditional areas of linguistic analysis include ...
es, added to the end of words: * -ad () and 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 () describes what is above something and inferior () describes what is below it. For example, in the
anatomical position The standard anatomical position, or standard anatomical model, is the scientifically agreed upon reference position for anatomical location terms. Standard anatomical positions are used to standardise the position of appendages An appendage ( ...

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 The neck is the part of the body on many vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With f ...

neck
is superior to the
chest The thorax or chest is a part of the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανι ...

chest
but inferior to the
head Head Sport GmbH is an American-Austrian manufacturing company headquartered in Kennelbach. It owns the American tennis racket brand Head. Head GmbH is a group that includes several previously independent companies, including the original "Head ...

head
.


Anterior and posterior

Anterior () describes what is in front, and posterior () describes what is to the back of something. For example, for a dog the
nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for Respiration (physiology), respiration alongside the mouth. Behind the nose are the olfactory mucosa and the Paranasal sinus, sinuses. Be ...

nose
is anterior to the eyes and the
tail The tail is the section at the rear end of certain kinds of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotrop ...
is considered the most posterior part; for many
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

fish
the
gill A gill () is a respiration organ, respiratory organ found in many aquatic ecosystem, aquatic organisms that extracts dissolved oxygen from water and excretes carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...
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 () describes something to the sides of an animal, as in "left lateral" and "right lateral". Medial () 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 torso or trunk is an anatomical terminology, anatomical term for the central part, or the core (anatomy), core, of the body (biology), body of many animals (including humans), from which the head, neck, limb (anatomy), limbs, tail and other a ...

torso
. The
genitals A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction Sexual reproduction is a type of reproduction that involves a complex Biological life cycle, life cycle in which a gamete (such as a sp ...
are medial to the legs. The terms "left" and "right" are sometimes used, or their Latin alternatives ( la, dexter, lit=right; la, 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 A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal, animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though throug ...
of a
dolphin Dolphin is the common name of aquatic mammals within the infraorder Cetacea. The term dolphin usually refers to the extant families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dol ...

dolphin
is "right of" the left
pectoral fin Fins are distinctive anatomical features composed of bony spine (zoology), spines or Ray (fish fin anatomy), rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony ...
, but is "left of" the right
eye Eyes are organs of the visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which ...

eye
, but much easier and clearer to say "the dorsal fin is medial to the pectoral fins". Terms derived from lateral include: * Contralateral (): 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 (): on the same side as another structure. For example, the left arm is ipsilateral to the left leg. * Bilateral (): on both sides of the body. For example, bilateral
orchiectomy Orchiectomy (also named orchidectomy, and sometimes shortened as orchi) is a surgery, surgical procedure in which one or both testicles are removed. The surgery is performed as treatment for testicular cancer, as part of Sex reassignment surgery ...
means removal of
testes Testicle or testis (plural testes) is the male reproductive gland or gonad in all animals, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primaril ...

testes
on both sides of the body. * Unilateral (): on one side of the body. For example, a
stroke A stroke is a medical condition A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. Dis ...

stroke
can result in unilateral
weakness Weakness is a symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressu ...
, meaning weakness on one side of the body. Varus () and valgus () 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

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. "Proximal and distal" are frequently used when describing
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are co ...
s, such as
fins A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people or ...

fins
,
tentacle with 2 tentacles and 8 arms In zoology Zoology ()The pronunciation of zoology as is typically regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the anatomy, structure, emb ...

tentacle
s, 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 Moiety may refer to: * Moiety (chemistry), a part or functional group of a molecule * Moiety (kinship), either of two groups into which a society is divided * A division of society in the Iroquois government and societal structure * An Australian Ab ...
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 The central nervous system (CNS) is the part of the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sensory information by transmi ...

Central nervous system
and the
peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sen ...
s. Central () describes something close to the centre. For example, the
great vessels Great vessels are the large vessels that bring blood to and from the heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped bloo ...
run centrally through the body; many smaller vessels branch from these. Peripheral (, originally from
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages () ...
) 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 () describes something further away from the surface of the organism. For example, the
external oblique muscle
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 Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventu ...
rather than Latin – the anglicised Latin term would have been "profound" (). Superficial () describes something near the outer surface of the organism. For example, in
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have differe ...

skin
, the
epidermis The epidermis is the outermost of the three layers that comprise the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Oth ...

epidermis
is superficial to the
subcutis The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, superficial fascia, is the lowermost layer of the integumentary system The integumentary system is the set of organs forming the outermost layer of an animal's body. ...
.


Dorsal and ventral

These two terms, used in anatomy and
embryology Embryology (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 mi ...
, describe something at the back (''dorsal'') or front/belly (''ventral'') of an organism. The dorsal () surface of an organism refers to the back, or upper side, of an organism. If talking about the skull, the dorsal side is the top. The ventral () surface refers to the front, or lower side, of an organism. For example, in a fish, the
pectoral fins Fins are distinctive anatomical features composed of bony spine (zoology), spines or Ray (fish fin anatomy), rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony ...
are dorsal to the
anal fin Fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust Thrust is a reaction (physics), reaction force (physics), force described quantitatively by ...
, but ventral to the
dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal, animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though throug ...
.


Cranial and caudal

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. * Cranial () or cephalic () describes how close something is to the head of an organism. * Caudal () describes how close something is to the trailing end of an organism. For example, in
horse The horse (''Equus ferus caballus'') is a Domestication, domesticated odd-toed ungulate, one-toed ungulate, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two Extant taxon, extant subspecies of wild horse, ''Equus ferus' ...

horse
s, the eyes are caudal to the nose and rostral to the back of the head. These terms are generally preferred in veterinary medicine and not used as often in human medicine.Hickman, C. P. Jr., Roberts, L. S. and Larson, A. ''Animal Diversity''. McGraw-Hill 2003 Miller, S. A. ''General Zoology Laboratory Manual'' McGraw-Hill, and In humans, "cranial" and "cephalic" are used to refer to the skull, with "cranial" being used more commonly. The term "rostral" is rarely used in human anatomy, apart from embryology, and refers more to the front of the face than the superior aspect of the organism. Similarly, the term "caudal" is used more in embryology and only occasionally used in human anatomy. This is because the brain is situated at the superior part of the head whereas the nose is situated in the anterior part. Thus, the "rostrocaudal axis" refers to a C shape (see image).


Other terms and special cases


Anatomical landmarks

The location of anatomical structures can also be described in relation to different
anatomical landmark Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mo ...
s. They are used in anatomy, surface anatomy, surgery, and radiology. Structures may be described as being at the level of a specific spinal vertebra, depending on the section of the
vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordata, ...

vertebral column
the structure is at. The position is often abbreviated. For example, structures at the level of the fourth
cervical vertebra In tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids (including ...

cervical vertebra
may be abbreviated as "C4", at the level of the fourth
thoracic vertebra The thorax or chest is a part of the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανι ...

thoracic vertebra
"T4", and at the level of the third
lumbar vertebra The lumbar vertebrae are, in human anatomy, the five vertebrae between the Human rib cage, rib cage and the Human pelvis, pelvis. They are the largest segments of the Human vertebral column, vertebral column and are characterized by the absence o ...
"L3". Because the
sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure ho ...

sacrum
and coccyx are fused, they are not often used to provide the location. References may also take origin from
superficial anatomy Surface anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ...
, made to landmarks that are on the skin or visible underneath. For example, structures may be described relative to the
anterior superior iliac spine The anterior superior iliac spine (abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full version of the w ...
, the
medial malleolus A malleolus is the bony prominence on each side of the human ankle The ankle, or the talocrural region, is the region where the foot and the human leg, leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the ...
or the medial epicondyle. Anatomical lines are used to describe anatomical location. For example, the mid-clavicular line is used as part of the cardiac exam in medicine to feel the of the
heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste ...

heart
.


Mouth and teeth

Special terms are used to describe the mouth and teeth. Fields such as
osteology 125px, A human skeleton (endoskeleton) Osteology, derived from the , is the science, scientific study of bones, practised by osteologists. A subdiscipline of anatomy, anthropology, and paleontology, osteology is the detailed study of the structure ...
,
palaeontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (geology), epoch (roughly 11,700 years before present). It includes th ...
and dentistry apply special terms of location to describe the mouth and teeth. This is because although teeth may be aligned with their main axes within the jaw, some different relationships require special terminology as well; for example, teeth also can be rotated, and in such contexts terms like "anterior" or "lateral" become ambiguous. For example, the terms "distal" and "proximal" are also redefined to mean the distance away or close to the
dental arch The dental arches are the two arches (crescent arrangements) of tooth, teeth, one on each jaw, that together constitute the dentition. In humans and many other species; the anatomical terms of location#Superior and inferior, superior (maxillary or ...
, and "medial" and "lateral" are used to refer to the closeness to the midline of the dental arch. Terms used to describe structures include "buccal" () and "palatal" () referring to structures close to the
cheek The cheeks ( la, buccae) constitute the area of the face below the human eye, eyes and between the Human nose, nose and the left or right ear. "Buccal" means relating to the cheek. In humans, the region is innervated by the buccal nerve. The are ...

cheek
and
hard palate The hard palate is a thin horizontal bony plate made up of two bones of the facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull The skull is a bone A bone is a Stiffness, ri ...
respectively.


Hands and feet

Several anatomical terms are particular to the hands and feet. Additional terms may be used to avoid confusion when describing the surfaces of the hand and what is the "anterior" or "posterior" surface. The term "anterior", while anatomically correct, can be confusing when describing the
palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand and a subdivision of the cubit * Palm trees, of family Arecaceae **List of Arecaceae genera * Several Arecaceae#Other plants, other plants known as Palm P ...

palm
of the hand; Similarly is "posterior", used to describe the back of the hand and arm. This confusion can arise because the forearm can
pronate Motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in which an object changes its position (mathematics), position over time. Motion is mathematically described in terms of ...
and
supinate Motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in which an object changes its position (mathematics), position over time. Motion is mathematically described in terms of ...
and flip the location of the hand. For improved clarity, the directional term palmar () is commonly used to describe the front of the hand, and dorsal is the back of the hand. For example, the top of a
dog The domestic dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated form of wolf. The dog descended from an ancient, extinct wolf, with the modern grey wolf being the dog's nearest living relative. The dog was the first ...

dog
's
paw A paw is the soft foot-like part of a mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which i ...
is its dorsal surface; the underside, either the palmar (on the forelimb) or the plantar (on the hindlimb) surface. The palmar fascia is ''palmar'' to the
tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant l ...

tendon
s of muscles which flex the fingers, and the
dorsal venous arch The dorsal venous arch of the foot is a superficial vein that connects the small saphenous vein The small saphenous vein (also short saphenous vein or lesser saphenous vein), is a relatively large superficial vein A superficial vein is a vein th ...
is so named because it is on the dorsal side of the foot. In humans, volar can also be used synonymously with ''palmar'' to refer to the underside of the
palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand and a subdivision of the cubit * Palm trees, of family Arecaceae **List of Arecaceae genera * Several Arecaceae#Other plants, other plants known as Palm P ...

palm
, but plantar is used exclusively to describe the sole. These terms describe location as '' palmar'' and ''
plantar Standard anatomical terms of location deal unambiguously with the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient ...
''; For example, ''volar'' pads are those on the underside of hands or fingers; the ''plantar'' surface describes the sole of the heel, foot or toes. Similarly, in the forearm, for clarity, the sides are named after the bones. Structures closer to the
radius In classical geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties ...
are radial, structures closer to the
ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in Standard anatomical position, anatomical position, is found on the Anatomical terms of location, medial side of ...

ulna
are ulnar, and structures relating to both bones are referred to as radioulnar. Similarly, in the lower leg, structures near the
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia), an ...

tibia
(shinbone) are tibial and structures near the
fibula The fibula or calf bone is a leg A leg is a weight-bearing and locomotive File:R707-loco-victorian-railways.jpg, upright=1.2, An Victorian Railways R class, R class steam locomotive number R707 as operated by the Victorian Railways of R ...

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 The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...

uterus
. * Anteversion () describes an anatomical structure being tilted further ''forward'' than normal, whether pathologically or incidentally. For example, a woman's
uterus The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...

uterus
typically is anteverted, tilted slightly ''forward''. A misaligned
pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen The abdomen (colloquially called the belly, tummy, midriff or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in o ...

pelvis
may be anteverted, that is to say tilted ''forward'' to some relevant degree. * Retroversion () describes an anatomical structure tilted ''back'' away from something. An example is a
retroverted uterus A retroverted uterus (tilted uterus, tipped uterus) is a uterus The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in t ...
.


Other directional terms

Several other terms are also used to describe location. These terms are not used to form the fixed axes. Terms include: * Axial (): around the central axis of the organism or the extremity. 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 The adventitia, () is the outer layer of fibrous connective tissue surrounding an organ (anatomy), organ. The outer layer of connective tissue that surrounds an artery, or vein – the tunica externa, is also called the ''tunica adventitia''. To ...
,
serosa In anatomy, serous membrane (or serosa) is a smooth membrane, tissue membrane of mesothelium lining the contents and inside wall of body cavity, body cavities, which secrete serous fluid to allow lubricated sliding (motion), sliding movements betw ...
, or the cavity's wall). * Parietal (): pertaining to the wall of a body cavity. For example, the
parietal peritoneum The peritoneum is the serous membrane In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργα ...
is the lining on the inside of the abdominal cavity. Parietal can also refer specifically to the
parietal bone The parietal bones () are two bones in the Human skull, skull which, when joined together at a fibrous joint, form the sides and roof of the Human skull, cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bor ...

parietal bone
of the skull or associated structures. * Terminal () at the extremity of a usually projecting structure. For example, "...an antenna with a terminal sensory hair". * Visceral and ''viscus'' (): associated with organs within the body's cavities. For example, the
stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital Digestion, digestive organ. ...

stomach
is covered with a lining called the visceral
peritoneum The peritoneum is the serous membrane In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργα ...

peritoneum
as opposed to the parietal peritoneum. Viscus can also be used to mean "organ". For example, the stomach is a viscus within the abdominal cavity, and ''visceral pain'' refers to pain originating from internal organs. *Aboral (opposite to oral) is used to denote a location along the
gastrointestinal canal The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of ...
that is relatively closer to the
anus The anus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

anus
.


Specific animals and other organisms

Different terms are used because of different
body plan A body plan, ''Bauplan'' (German plural ''Baupläne''), or ground plan is a set of morphological features common to many members of a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ) ...
s in animals, whether animals stand on one or two legs, and whether an animal is symmetrical or not, as discussed above. For example, as humans are approximately
bilaterally symmetrical Symmetry in biology refers to the symmetry observed in organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties o ...
organisms, anatomical descriptions usually use the same terms as those for other vertebrates. However, humans stand upright on two legs, meaning their anterior/posterior and ventral/dorsal directions are the same, and the inferior/superior directions are necessary. Humans do not have a
beak The beak, bill, and/or rostrum is an external anatomical structure found mostly in birds Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, the Ovi ...

beak
, so a term such as "rostral" used to refer to the beak in some animals is instead used to refer to part of the brain; humans do also not have a tail so a term such as "caudal" that refers to the tail end may also be used in humans and animals without tails to refer to the hind part of the body. In
invertebrates Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart from the chordata, chordate subphylum vertebrate, Vertebrat ...
, the large variety of body shapes presents a difficult problem when attempting 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 A body plan, ''Bauplan'' (German plural ''Baupläne''), or ground plan is a set of morphological features common to many members of a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ) ...
of the organism. 662px-Anatomical-directions.png, Anatomical terms of location in a
dog The domestic dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated form of wolf. The dog descended from an ancient, extinct wolf, with the modern grey wolf being the dog's nearest living relative. The dog was the first ...

dog
Anatomical-directions-kangaroo.svg, Anatomical terms of location in a
kangaroo The kangaroo is a marsupial Marsupials are any members of the mammalian Class (biology), infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of t ...

kangaroo
Anatomical Directions and Axes.JPG, Anatomical terms of location in a
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

fish
. Horse Axes.JPG, Anatomical terms of location in a
horse The horse (''Equus ferus caballus'') is a Domestication, domesticated odd-toed ungulate, one-toed ungulate, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two Extant taxon, extant subspecies of wild horse, ''Equus ferus' ...

horse
.


Asymmetrical and spherical organisms

. (a) An organism with an asymmetrical, amoeboid, body plan (''Amoeba proteus'' an amoeba). (b) An organism with a spherical body plan (''Actinophrys sol'' a
heliozoan Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes Eukaryotes () are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embod ...
). In organisms with a changeable shape, such as
amoeboid An amoeba (; less commonly spelt ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism A unicellular organism, also known as a single-celled organism, is an organism ...
organisms, most directional terms are meaningless, since the shape of the organism is not constant and no distinct axes are fixed. Similarly, in spherically 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. with a fixed elongated shape.


Elongated organisms

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 Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocea ...
(free-swimming)
protists A protist () is any eukaryotic organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym f ...
, and are nearly always viewed on
microscope slide 240px, A microscope slide (top) and a cover slip (bottom) A microscope slide is a thin flat piece of glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technol ...

microscope slide
s, where they appear essentially two-dimensional. In some cases a third axis can be defined, particularly where a non-terminal
cytostome A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving ris ...
or other unique structure is present. Some elongated
protists A protist () is any eukaryotic organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym f ...
have distinctive ends of the body. In such organisms, the end with a mouth (or equivalent structure, such as the
cytostome A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving ris ...
in ''Paramecium'' or ''Stentor''), or the end that usually points in the direction of the organism's Animal locomotion, 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. Properly, this terminology would apply only to an organism that is always
planktonic Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocea ...
(not normally attached to a surface), although the term can also be applied to one that is Sessility (zoology), sessile (normally attached to a surface). Image:Venus Flower Basket (sponge-labelled).JPG, A cluster of Venus' Flower Basket, ''Euplectella aspergillum'' sponges (Venus flower baskets), showing the apical-basal axes. Organisms that are attached to a Substrate (biology), substrate, such as Porifera, sponges, Protista, 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

Radial symmetry, Radially symmetrical organisms include those in the group Radiata primarily Cnidaria, jellyfish, sea anemones and corals and the Ctenophora, comb jellies. Adult Echinodermata, echinoderms, such as starfish, sea urchins, sea cucumbers and others are also included, since they are pentaradial, meaning they have five rotational symmetry#n-fold rotational symmetry, discrete rotational symmetry (biology), symmetry. Echinoderm larvae are not included, since they are
bilaterally symmetrical Symmetry in biology refers to the symmetry observed in organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties o ...
. Radially symmetrical organisms always have one distinctive axis. Cnidarians (jellyfish, sea anemones and corals) have an incomplete digestive system, meaning that one end of the organism has a mouth, and the opposite end has no opening from the gut (coelenteron). For this reason, the end of the organism with the mouth is referred to as the oral end (), and the opposite surface is the aboral end (). Unlike vertebrates, cnidarians have no other distinctive axes. "Lateral", "dorsal", and "ventral" have no meaning in such organisms, and all can be replaced by the generic term peripheral (). Medial can be used, but in the case of radiates indicates the central point, rather than a central axis as in vertebrates. Thus, there are multiple possible radial axes and medio-peripheral (half-) axes. However, some biradially symmetrical Ctenophora, comb jellies do have distinct "tentacular" and "pharyngeal" axesRuppert ''et al.'' (2004), p. 184. and are thus anatomically equivalent to bilateria, bilaterally symmetrical animals. 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 specialized terms are useful in describing views of arachnid legs and pedipalps. 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 taxon, 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

* Geometric terms of location * Handedness * Laterality * Proper right and proper left * Reflection symmetry * Sinistral and dextral


References


Sources

* * * * * * * {{DEFAULTSORT:Anatomical Terms Of Location Anatomy, Animal anatomy Medical terminology Orientation (geometry) Position