View source for Biology:Anatomical terms of location

{{Short description|Standard terms for unambiguous description of relative placement of body parts}}
{{Anatomical terminology series}}

Standard '''anatomical terms of location''' are used to unambiguously describe the [[Biology:Anatomy|anatomy]] of [[Biology:Animal|animal]]s, including [[Biology:Human|human]]s. The terms, typically derived from [[Social:Latin|Latin]] or [[Social:Greek language|Greek]] roots, describe something in its [[Biology:Standard anatomical position|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 [[Biology:Anatomical plane|anatomical plane]]s and anatomical axes.

The meaning of terms that are used can change depending on whether an organism is bipedal or quadrupedal. Additionally, for some animals such as [[Biology:Invertebrate|invertebrate]]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 standards for subdisciplines of anatomy. For example, ''[[Biology:Terminologia Anatomica|Terminologia Anatomica]]'' for humans and ''[[Biology:Nomina Anatomica Veterinaria|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==
[[File:Human Neuroaxis-en.svg|thumbnail|300px|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 [[Biology:Anatomy|anatomical]] and [[Biology:Zoology|zoological]] terms of location have been developed, usually based on Latin and [[Social:Greek language|Greek]] words, to enable all biological and medical scientists, veterinarians, [[Medicine:Physician|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.{{sfn|Dyce|Sack|Wensing|2010|pp=2–3}}{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}} Much of this information has been standardised in internationally agreed vocabularies for humans ([[Biology:Terminologia Anatomica|Terminologia Anatomica]]){{sfn|Gray's Anatomy|2016|pp=xvi-xvii}} and animals ([[Biology:Nomina Anatomica Veterinaria|Nomina Anatomica Veterinaria]]).{{sfn|Dyce|Sack|Wensing|2010|pp=2–3}}

Different terms are used for groups of creatures with different body layouts, such as bipeds (creatures that stand on two feet, such as humans) and quadrupeds.{{sfn|Dyce|Sack|Wensing|2010|pp=2–3}} The reasoning is that the [[Biology:Neuraxis|neuraxis]] is different between the two groups, and so is what is considered the [[Biology:Standard anatomical position|standard anatomical position]], such as how humans tend to be standing upright and with their arms reaching forward.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}} Thus, the "top" of a human is the head, whereas the "top" of a dog would be the back, and the "top" of a [[Biology:Flounder|flounder]] may be on either the left or right side. Unique terms are also used to describe [[Biology:Invertebrate|invertebrate]]s as well, because of their wider variety of shapes and symmetry.{{sfn|Kardong's|2019|p=16}} 

===Standard anatomical position===
{{Main|Biology:Standard anatomical position}}
[[File:Anatomical position.jpg|thumb|A male and female human in the standard anatomical position]]

Because [[Biology:Animal|animal]]s can change orientation with respect to their environment, and because [[Biology:Appendage|appendage]]s like limbs and [[Biology:Tentacle|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 [[Biology:Standard anatomical position|standard anatomical position]].{{sfn|Dyce|Sack|Wensing|2010|pp=2–3}} 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.{{sfn|Dyce|Sack|Wensing|2010|pp=2–3}} 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.{{sfn|Gray's Anatomy|2016|pp=xvi–xvii}}{{sfn|Dyce|Sack|Wensing|2010|pp=2–3}}
{{clear}}

=== Combined terms ===
[[File:Holotype of Mantophryne insignis, dorsolateral view.jpg|thumb|Anatomical terms can be combined to be more specific. This is a '''dorsolateral''' view of the [[Biology:Frog|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 [[Medicine:Radiology|radiology]], an [[Physics:X-ray|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.<ref>{{cite book |last1=Hofer |first1=Matthias |title=The Chest X-ray: A Systematic Teaching Atlas |year=2006 |publisher=Thieme |isbn=978-3-13-144211-6 |page=24 |url=https://books.google.com/books?id=iERHEAWOk3oC&pg=PA24 |language=en}}</ref> Combined terms were once generally hyphenated, but the modern tendency is to omit the hyphen.<ref>{{cite dictionary |url=http://www.merriam-webster.com/dictionary/dorsolateral |title=dorsolateral |date=29 September 2023 |dictionary=Merriam-Webster}}</ref>
{{clear}}

===Planes===
{{Main|Biology:Anatomical plane}}
[[File:Human anatomy planes, labeled.svg|thumb|right|299px|Anatomical planes in a human]]

Anatomical terms describe structures with relation to four main [[Biology:Anatomical plane|anatomical plane]]s:{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}}

# The '''median plane''', which divides the body into left and right.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}}{{sfn|Wake|1992|p=6}} This passes through the head, [[Biology:Spinal cord|spinal cord]], navel, and, in many animals, the [[Biology:Tail|tail]].{{sfn|Wake|1992|p=6}}
# The '''[[Biology:Sagittal plane|sagittal plane]]s''', which are {{wt|en|parallel}} to the median plane.{{sfn|Dyce|Sack|Wensing|2010|pp=2–3}}
# The '''frontal plane''', also called the '''[[Biology:Coronal plane|coronal plane]]''', which divides the body into front and back.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}}
# The '''horizontal plane''', also known as the '''[[Biology:Transverse plane|transverse plane]]''', which is perpendicular to the other two planes.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}} In a human, this plane is parallel to the ground; in a quadruped, this divides the animal into anterior and posterior sections.{{sfn|Kardong's|2019|p=16}}
{{clear}}

===Axes===
<!--Multiple links redirect to this section-->
[[Image:Labelled Ciliates.JPG|thumb|Organisms where the ends of the long axis are distinct. (''Paramecium caudatum'', above, and ''[[Biology:Stentor roeselii|Stentor roeselii]]'', below.)]]

The axes of the body are lines drawn about which an organism is roughly symmetrical.{{sfn|Collins|2020|loc="axis", accessed 17 July 2020}} 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|right angle]]s.{{sfn|Kardong's|2019|p=16}} An organism that is round or not symmetrical may have different axes.{{sfn|Kardong's|2019|p=16}} Example axes are:

* The anteroposterior axis{{sfn|Merriam-Webster|2020|loc="Anteroposterior", accessed 14 October 2020}}
* The cephalocaudal axis{{sfn|Merriam-Webster|2020|loc="Cephalocaudal", accessed 14 October 2020}}
* The dorsoventral axis{{sfn|Merriam-Webster|2020|loc="Dorsoventral", accessed 14 October 2020}}

Examples of axes in specific animals are shown below.
<gallery>
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 [[Biology:Fish|fish]]
Long and short axis.png|[[Spheroid]] or near-spheroid organs such as testes may be measured by ''long'' and ''short'' axes.<ref>{{cite book|title=Introduction to Vascular Ultrasonography|first1=John |last1=Pellerito |first2=Joseph F. |last2=Polak|edition=6th|publisher=Elsevier Health Sciences|year=2012|isbn=978-1-4557-3766-6 |page=[https://books.google.com/books?id=safNmcP3lakC&pg=PA559 559]}}</ref>
</gallery>
{{clear}}

===Modifiers===
[[File:Radiate Oral-aboral Axes.JPG|thumbnail|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 [[Social:Prefix|prefix]]es:

* '''Sub-''' ({{ety|la|sub|preposition beneath, close to, nearly etc}}) is used to indicate something that is beneath, or something that is subordinate to or lesser than.{{sfn|Merriam-Webster|2020|loc="Sub-", accessed on 3 July 2020}} For example, [[Biology:Subcutaneous tissue|subcutaneous]] means beneath the skin.
* '''Hypo-''' ({{ety|grc|ὑπό|under}}) is used to indicate something that is beneath.{{sfn|Merriam-Webster|2020|loc="Hypo-", accessed on 3 July 2020}} For example, the [[Biology:Hypoglossal nerve|hypoglossal nerve]] supplies the muscles beneath the tongue.
* '''Infra-''' ({{ety|la|infra|under}}) is used to indicate something that is within or below.{{sfn|Merriam-Webster|2020|loc="Infra-", accessed on 3 July 2020}} For example, the infraorbital nerve runs within the [[Biology:Orbit (anatomy)|orbit]].
* '''Inter-''' ({{ety|la|inter|between}}) is used to indicate something that is between.{{sfn|Merriam-Webster|2020|loc="Inter-", accessed on 3 July 2020}} For example, the intercostal muscles run between the [[Biology:Rib|rib]]s.
* '''Super-'' or ''Supra-''' ({{ety|la|super, supra|above, on top of}}) is used to indicate something that is above something else.{{sfn|Merriam-Webster|2020|loc="Super-" and "Supra-", accessed on 3 July 2020}} For example, the supraorbital ridges are above the [[Biology:Eye|eye]]s.

Other terms are used as [[Social:Suffix|suffix]]es, added to the end of words:
* '''-ad''' ({{ety|la|ad|towards}}) and '''-ab''' ({{ety|la|ab}}) are used to indicate that something is towards (-ad) or away from (-ab) something else.{{sfn|Merriam-Webster|2020|loc="-ad", accessed on 3 July 2020}}{{sfn|Merriam-Webster|2020|loc="an-", accessed on 17 July 2020}} 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.<ref name= "GGHDHD">{{cite book |last1=Gordh |first1=Gordon |last2=Headrick |first2=David H |title=A Dictionary of Entomology |publisher=CABI |year=2011 |edition=2nd |isbn=978-1845935429|url=https://archive.org/details/dictionaryofento0000gord}}</ref>

==Main terms==
{{Anchor|superior|inferior}}
===Superior and inferior===
 <!-- Posterior is a dab page, not redirect -->

'''Superior''' ({{ety|la|super|above}}) describes what is above something{{sfn|Collins|2020|loc="superior", accessed 2 July 2020}} and '''inferior''' ({{ety|la|inferus|below}}) describes what is below it.{{sfn|Collins|2020|loc="inferior", accessed 2 July 2020}} 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 [[Medicine:Neck|neck]] is superior to the chest but inferior to the [[Medicine:Human head|head]].

===Anterior and posterior===
'''Anterior''' ({{ety|la|ante|before}}) describes what is in front,{{sfn|Collins|2020|loc="anterior", accessed 2 July 2020}} and '''posterior''' ({{ety|la|post|after}}) describes what is to the back of something.{{sfn|Collins|2020|loc="posterior", accessed 2 July 2020}} For example, for a dog the [[Medicine:Nose|nose]] is anterior to the eyes and the [[Biology:Tail|tail]] is considered the most posterior part; for many [[Biology:Fish|fish]] the [[Biology:Gill|gill]] openings are posterior to the eyes but anterior to the tail.

{{Anchor|medial|median|lateral}}
===Medial and lateral<span class="anchor" id="unilateral"></span><span class="anchor" id="bilateral"></span><span class="anchor" id="temporal"></span>===
These terms describe how close something is to the midline, or the medial plane.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}} '''Lateral''' ({{ety|la|lateralis|to the side}}) describes something to the sides of an animal, as in "left lateral" and "right lateral". '''Medial''' ({{ety|la|medius|middle}}) describes structures close to the midline,{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}} or closer to the midline than another structure. For example, in a human, the arms are lateral to the torso. The [[Biology:Sex organ|genitals]] are medial to the legs. '''Temporal''' has a similar meaning to lateral but is restricted to the head.

The terms "left" and "right" are sometimes used, or their Latin alternatives ({{lang-la|dexter|lit=right}}; {{lang-la|sinister|lit=left}}). However, it is preferred to use more precise terms where possible. 

Terms derived from lateral include:

* '''Contralateral''' ({{ety|la|contra|against}}): on the side opposite to another structure.{{sfn|Collins|2020|loc="contralateral", accessed 2 July 2020}} For example, the right arm and leg are controlled by the left, [[Biology:Contralateral brain|contralateral, side of the brain]].
* '''Ipsilateral''' ({{ety|la|ipse|same}}): on the same side as another structure.{{sfn|Collins|2020|loc="ipsilateral", accessed 2 July 2020}} For example, the left arm is ipsilateral to the left leg.
* '''Bilateral''' ({{ety|la|bis|twice}}): on both sides of the body.{{sfn|Collins|2020|loc="bilateral", accessed 2 July 2020}} For example, bilateral [[Medicine:Orchiectomy|orchiectomy]] means removal of testes on both sides of the body.
* '''Unilateral''' ({{ety|la|unus|one}}): on one side of the body.{{sfn|Collins|2020|loc="unilateral", accessed 2 July 2020}} For example, a [[Medicine:Stroke|stroke]] can result in unilateral [[Medicine:Paresis|weakness]], meaning weakness on one side of the body.

'''[[Medicine:Varus deformity|Varus]]''' ({{ety|la||bow-legged}}) and '''[[Medicine:Valgus deformity|valgus]]''' ({{ety|la||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.{{sfn|Collins|2020|loc="varus" and "valgus", accessed 17 July 2020}}

{{Anchor|proximal|distal}}

===Proximal and distal===
[[File:Blausen 0019 AnatomicalDirectionalReferences.png|thumb|350px|Anatomical directional reference]]

The terms '''proximal''' ({{ety|la|proximus|nearest}}) and '''distal''' ({{ety|la|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.{{sfn|Wake|1992|p=5}} Thus the upper arm in humans is proximal and the hand is distal.

"Proximal and distal" are frequently used when describing [[Biology:Appendage|appendage]]s, such as fins, [[Biology:Tentacle|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.<ref>{{cite web |title=What do distal and proximal mean? |website=The Survival Doctor |url=http://www.thesurvivaldoctor.com/2011/10/04/what-do-distal-and-proximal-mean/ |access-date=2016-01-07|date=2011-10-05 }}</ref>

The terms are also applied to internal anatomy, such as to the [[Biology:Reproductive system of gastropods|reproductive tract of snails]]. Unfortunately then different authors use the terms in opposite senses. Some consider distal as further from a point of origin near the centre of the body and others as further from where the organ reaches the body's surface; or other points of origin may be envisaged.<ref>{{cite journal |last1=Hutchinson |first1=J.M.C. |title=Lippen are not lips, and other nomenclatural confusions |journal=Mitteilungen der Deutschen Malakozoologischen Gesellschaft |date=2022 |volume=107 |pages=3–7 |url=https://malagr.de/hutch/hutchpub/mdmg8.htm}}</ref>

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 [[Chemistry:Moiety|moiety]] of a given compound.<ref>{{cite journal|last1=Singh|first1=S|title=Chemistry, design, and structure-activity relationship of cocaine antagonists.|journal=Chemical Reviews|date=8 March 2000|volume=100|issue=3|pages=925–1024|pmid=11749256|doi=10.1021/cr9700538}}</ref>

===Central and peripheral===
'''Central''' and '''peripheral''' refer to the distance towards and away from the centre of something.{{sfn|Collins|2020|loc="central", accessed 17 July 2020}} That might be an organ, a region in the body, or an anatomical structure. For example, the [[Biology:Central nervous system|central nervous system]] and the [[Biology:Peripheral nervous system|peripheral nervous system]]s.

'''Central''' ({{ety|la|centralis}}) describes something close to the centre.{{sfn|Collins|2020|loc="central", accessed 17 July 2020}} For example, the [[Biology:Great vessels|great vessels]] run centrally through the body; many smaller vessels branch from these.

'''Peripheral''' ({{ety|la|peripheria}}, originally from [[Social:Ancient Greek|Ancient Greek]]) describes something further away from the centre of something.{{sfn|Collins|2020|loc="peripheral", accessed 17 July 2020}} For example, the arm is peripheral to the body.

{{Anchor|superficial|deep}}

===Superficial and deep===
These terms refer to the distance of a structure from the surface.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}}

'''Deep''' ({{ety|ang}}) describes something further away from the surface of the organism.{{sfn|Collins|2020|loc="deep", accessed 2 July 2020}} 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 [[Social:Old English|Old English]] rather than Latin – the anglicised Latin term would have been "profound" ({{ety|la|profundus|due to depth}}).{{sfn|Dyce|Sack|Wensing|2010|pp=2–3}}{{sfn|Collins|2020|loc="profound", accessed 2 July 2020}}

'''Superficial''' ({{ety|la|superficies|surface}}) describes something near the outer surface of the organism.{{sfn|Dyce|Sack|Wensing|2010|pp=2–3}}{{sfn|Collins|2020|loc="superficial", accessed 2 July 2020}} For example, in [[Biology:Skin|skin]], the [[Biology:Epidermis|epidermis]] is superficial to the subcutis.

===Dorsal and ventral===
These two terms, used in anatomy and [[Biology:Embryology|embryology]], describe something at the back (''dorsal'') or front/belly (''ventral'') of an organism.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}}

The '''dorsal''' ({{ety|la|dorsum|back}}) 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.{{sfn|GO|2014|loc="dorsal/ventral axis specification" (GO:0009950)}}

{{anchor|inserted2020-09-25specificallyfor ventral}}
The '''ventral''' ({{ety|la|venter|belly}}) surface refers to the front, or lower side, of an organism.{{sfn|GO|2014|loc="dorsal/ventral axis specification" (GO:0009950)}}

For example, in a fish, the pectoral fins are dorsal to the anal fin, but ventral to the dorsal fin.

{{Anchor|caudal|cranial|rostral}}
===Rostral, cranial, and caudal===
[[File:Rostralcaudal.svg|thumb|right|In the human skull, 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''' ({{ety|la|rostrum|beak, nose}}) describes something situated toward the oral or nasal region, or in the case of the brain, toward the tip of the frontal lobe.{{sfn|Merriam-Webster|2020|loc="rostral", accessed 3 July 2020}}
* '''Cranial''' ({{ety|el|κρανίον|skull}}) or '''cephalic''' ({{ety|el|κεφαλή|head}}) describes how close something is to the head of an organism.{{sfn|Merriam-Webster|2020|loc="cranial" and "cephalic", accessed 3 July 2020}}
* '''Caudal''' ({{ety|la|cauda|tail}}) describes how close something is to the trailing end of an organism.{{sfn|Merriam-Webster|2020|loc="caudal", accessed 3 July 2020}}

For example, in [[Biology:Horse|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.<ref name="Hickman et al. 2003">Hickman, C. P. Jr., Roberts, L. S. and Larson, A. ''Animal Diversity''. McGraw-Hill 2003 {{ISBN|0-07-234903-4}}</ref><ref name="Miller 2002">Miller, S. A. ''General Zoology Laboratory Manual'' McGraw-Hill, {{ISBN|0-07-252837-0}} and {{ISBN|0-07-243559-3}}</ref><ref name="Ruppert2004">{{cite book |last1=Ruppert |first1=EE |last2=Fox |first2=RS |last3=Barnes |first3=RD |title=Invertebrate zoology : a functional evolutionary approach |date=2004 |publisher=Thomson-Brooks/Cole |location=Thomson, Belmont |isbn=0-03-025982-7 |edition=7th}}</ref> 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.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}} 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 landmarks. They are used in anatomy, surface anatomy, surgery, and radiology.<ref name=":0">{{Cite book|last1=Butler|first1=Paul|url=https://books.google.com/books?id=YaYSbU6DR9oC&q=surface+anatomy+and+anatomical+landmarks&pg=PA1|title=Applied Radiological Anatomy|last2=Mitchell|first2=Adam W. M.|last3=Ellis|first3=Harold|date=1999-10-14|publisher=Cambridge University Press|isbn=978-0-521-48110-6|pages=1|language=en}}</ref>

Structures may be described as being at the level of a specific spinal vertebra, depending on the section of the [[Biology:Vertebral column|vertebral column]] the structure is at.<ref name=":0" /> The position is often abbreviated. For example, structures at the level of the fourth cervical vertebra may be abbreviated as "C4", at the level of the fourth thoracic vertebra "T4", and at the level of the third lumbar vertebra "L3". Because the [[Biology:Sacrum|sacrum]] and coccyx are fused, they are not often used to provide the location.

References may also take origin from superficial anatomy, made to landmarks that are on the skin or visible underneath.<ref name=":0" /> For example, structures may be described relative to the [[Biology:Anterior superior iliac spine|anterior superior iliac spine]], the medial malleolus or the medial epicondyle.

[[Medicine:List of anatomical lines|Anatomical lines]] are used to describe anatomical location. For example, the mid-clavicular line is used as part of the [[Medicine:Cardiac examination|cardiac exam]] in medicine to feel the [[Medicine:Apex beat|apex beat]] of the [[Biology:Heart|heart]].

===Mouth and teeth===

Special terms are used to describe the mouth and teeth.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}} Fields such as [[Biology:Osteology|osteology]], palaeontology 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.<ref name="Folkens2000">{{cite book|author=Pieter A. Folkens|title=Human Osteology|url=https://books.google.com/books?id=lrLL-X5bg_0C&pg=PA558|year=2000|publisher=Gulf Professional Publishing|isbn=978-0-12-746612-5|pages=558–}}</ref><ref name=SmithDodson2003>{{cite journal |last1=Smith |first1=J. B. |last2=Dodson |first2=P. |year=2003 |title=A proposal for a standard terminology of anatomical notation and orientation in fossil vertebrate dentitions |journal=Journal of Vertebrate Paleontology |volume=23 |issue=1 |pages=1–12 |doi=10.1671/0272-4634(2003)23[1:APFAST]2.0.CO;2 |s2cid=8134718 |url=https://repository.upenn.edu/ees_papers/34 }}</ref> For example, the terms "distal" and "proximal" are also redefined to mean the distance away or close to the dental arch, and "medial" and "lateral" are used to refer to the closeness to the midline of the dental arch.<ref name=Rajkumar2017>{{cite book |last1=Rajkumar |first1=K. |last2=Ramya |first2=R. |title=Textbook of Oral Anatomy, Physiology, Histology and Tooth Morphology |publisher=Wolters kluwer india Pvt Ltd |isbn=978-93-86691-16-3 |pages=6–7 |url=https://books.google.com/books?id=YvbsDwAAQBAJ&dq=distal+and+%22proximal+mandibular+symphysis+dental+anatomy&pg=RA1-PA7 |language=en|year=2017}}</ref> Terms used to describe structures include "buccal" ({{ety|la|bucca|cheek}}) and "palatal" ({{ety|la|palatum|palate}}) referring to structures close to the [[Medicine:Cheek|cheek]] and [[Medicine:Hard palate|hard palate]] respectively.<ref name=Rajkumar2017 />

===Hands and feet===
[[Image:Hand Directional Axes.JPG|thumb|right|Anatomical terms used to describe a human hand]]

Several anatomical terms are particular to the hands and feet.{{sfn|Gray's Anatomy|2016|pp=xvi-xvii}}

Additional terms may be used to avoid confusion when describing the surfaces of the hand and what is the "anterior" or "posterior" surface{{snd}}. The term "anterior", while anatomically correct, can be confusing when describing the 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 and supinate and flip the location of the hand. For improved clarity, the directional term '''palmar''' ({{ety|la|palma|palm of the hand}}) is commonly used to describe the front of the hand, and '''dorsal''' is the back of the hand. For example, the top of a [[Biology:Dog|dog]]'s [[Biology:Paw|paw]] 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 [[Biology:Tendon|tendon]]s of muscles which flex the fingers, and the dorsal venous arch 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, but '''plantar''' is used exclusively to describe the  sole. These terms describe location as ''palmar'' and ''plantar''; 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 [[Biology:Radius (bone)|radius]] are '''radial''', structures closer to the [[Biology:Ulna|ulna]] are '''ulnar''', and structures relating to both bones are referred to as '''radioulnar'''. Similarly, in the lower leg, structures near the [[Biology:Tibia|tibia]] (shinbone) are '''tibial''' and structures near the [[Biology:Fibula|fibula]] are '''fibular''' (or '''peroneal''').

===Rotational direction===
{{multiple image
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 | image1 = Gray1230.png
 | image2 = Atlas and epitome of gynecology (1900) (14761581924).jpg
 | footer = Image showing an '''anteverted''' [[Biology:Uterus|uterus]] lying above the [[Biology:Urinary bladder|bladder]] (left), compared with a '''retroverted''' uterus undergoing bimanual examination facing towards the [[Biology:Rectum|rectum]] (right)
}}

'''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 [[Biology:Uterus|uterus]].{{sfn|Collins|2020|loc="anteversion", accessed 17 July 2020}}{{sfn|Collins|2020|loc="retroversion", accessed 17 July 2020}}
* '''Anteversion''' ({{ety|la|anteversus}}) describes an anatomical structure being tilted further ''forward'' than normal, whether pathologically or incidentally.{{sfn|Collins|2020|loc="anteversion", accessed 17 July 2020}} For example, a woman's [[Biology:Uterus|uterus]] typically is anteverted, tilted slightly ''forward''. A misaligned [[Biology:Pelvis|pelvis]] may be anteverted, that is to say tilted ''forward'' to some relevant degree.
* '''Retroversion''' ({{ety|la|retroversus}}) describes an anatomical structure tilted ''back'' away from something.{{sfn|Collins|2020|loc="retroversion", accessed 17 July 2020}} An example is a retroverted uterus.{{sfn|Collins|2020|loc="retroversion", accessed 17 July 2020}}

===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''' ({{ety|la|axis|axle}}): 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''' ({{ety|la|lumen|light, opening}}): on the—hollow—inside of an organ's [[Biology:Lumen (anatomy)|lumen]] (body cavity or tubular structure);<ref>{{cite web|url=https://www.medicinenet.com/lumen/definition.htm |title=Medical Definition of Lumen |author=William C. Shiel |publisher=MedicieNet |access-date=12 December 2020}}</ref><ref>{{cite web|url=https://www.cancer.gov/publications/dictionaries/cancer-terms/def/lumen |title=NCI Dictionary of Cancer Terms "lumen" |publisher=[[Organization:National Cancer Institute|National Cancer Institute]] |access-date=12 December 2020}}</ref> '''adluminal''' is towards, '''abluminal''' is away from the lumen.<ref>{{cite web|url=https://www.merriam-webster.com/medical/abluminal |work=Merriam-Webster.com Medical Dictionary |title="abluminal"|access-date=12 December 2020}}</ref> Opposite to '''outermost''' (the adventitia,  serosa, or the cavity's wall).<ref>{{cite web|url=http://www.siumed.edu/~dking2/erg/giguide.htm |title=Study Guide - Histology of the Gastrointestinal System |publisher=Southern Illinois University |author=David King |year=2009 |access-date=12 December 2020}}</ref>
* '''Parietal''' ({{ety|la|paries|wall}}): pertaining to the wall of a body cavity.{{sfn|Merriam-Webster|2020|loc="parietal", accessed 3 July 2020}} For example, the parietal peritoneum is the lining on the inside of the abdominal cavity. Parietal can also refer specifically to the [[Biology:Parietal bone|parietal bone]] of the skull or associated structures.
* '''Terminal''' ({{ety|la|terminus|boundary or end}}) at the extremity of a usually projecting structure.{{sfn|Merriam-Webster|2020|loc="terminal", accessed 3 July 2020}} For example, "...an antenna with a terminal sensory hair".
* '''Visceral''' and ''viscus'' ({{ety|la|viscera|internal organs}}): associated with organs within the body's cavities.{{sfn|Merriam-Webster|2020|loc="visceral", accessed 3 July 2020}} For example, the [[Biology:Stomach|stomach]] is covered with a lining called the visceral peritoneum as opposed to the parietal peritoneum. Viscus can also be used to mean "organ".{{sfn|Merriam-Webster|2020|loc="visceral", accessed 3 July 2020}} 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 that is relatively closer to the [[Biology:Anus|anus]].<ref name="MorricePolton2019">{{cite journal|last1=Morrice|first1=Michael|last2=Polton|first2=Gerry|last3=Beck|first3=Sam|title=Evaluation of the extent of neoplastic infiltration in small intestinal tumours in dogs|journal=Veterinary Medicine and Science|volume=5|issue=2|year=2019|pages=189–198|issn=2053-1095|doi=10.1002/vms3.147|pmid=30779310|pmc=6498519|doi-access=free}}</ref>

==Specific animals and other organisms==
Different terms are used because of different [[Biology:Body plan|body plan]]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 [[Biology:Symmetry in biology|bilaterally symmetrical]] organisms, anatomical descriptions usually use the same terms as those for other vertebrates.{{sfn|Wake|1992|p=1}} 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.<ref name= "Latin Tucker">{{cite book | author= Tucker, T. G.| title = A Concise Etymological Dictionary of Latin | publisher = Max Niemeyer Verlag | location = Halle (Saale)| year = 1931 }}</ref> Humans do not have a 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;{{sfn|Merriam-Webster|2020|loc="rostral", accessed 14 October 2020}} 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.{{sfn|Merriam-Webster|2020|loc="caudal", accessed 14 October 2020}}

In invertebrates, 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 [[Biology:Body plan|body plan]] of the organism.

<gallery>
Direcoes anatomicas.svg|Anatomical terms of location in a [[Biology:Dog|dog]]
Anatomical-directions-kangaroo.svg|Anatomical terms of location in a [[Biology:Kangaroo|kangaroo]]
Anatomical Directions and Axes.JPG|Anatomical terms of location in a [[Biology:Fish|fish]]
Horse Axes.JPG|Anatomical terms of location in a [[Biology:Horse|horse]]
</gallery>

===Asymmetrical and spherical organisms===
[[Image:Asymmetrical and Spherical.JPG|thumb|right|250px|Asymmetrical and spherical [[Biology:Body plan|body shapes]]. (a) An organism with an asymmetrical, amoeboid body plan (''Amoeba proteus''{{snd}} an amoeba). (b) An organism with a spherical body plan (''Actinophrys sol''{{snd}} a heliozoan).]]

In 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 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.
[[Image:Longitudinal Diatom (Labelled).JPG|thumb|right|Four individuals of ''Phaeodactylum tricornutum'', a [[Biology:Diatom|diatom]] 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 (free-swimming) protists, and are nearly always viewed on [[Physics:Microscope slide|microscope slide]]s, where they appear essentially two-dimensional. In some cases a third axis can be defined, particularly where a non-terminal [[Biology:Cytostome|cytostome]] or other unique structure is present.<ref name="Ruppert2004" />

<!-- Apical (anatomy) and Basal (anatomy) redirect here -->Some elongated protists have distinctive ends of the body. In such organisms, the end with a mouth (or equivalent structure, such as the [[Biology:Cytostome|cytostome]] in ''[[Biology:Paramecium|Paramecium]]'' or ''[[Biology:Stentor (ciliate)|Stentor]]''), or the end that usually points in the direction of the organism's [[Biology:Animal locomotion|locomotion]] (such as the end with the [[Biology:Flagellum|flagellum]] in ''[[Biology:Euglena|Euglena]]''), is normally designated as the '''anterior''' end. The opposite end then becomes the '''posterior end'''.<ref name="Ruppert2004" /> Properly, this terminology would apply only to an organism that is always planktonic (not normally attached to a surface), although the term can also be applied to one that is sessile (normally attached to a surface).<ref>{{cite book |title=On the Origin of Phyla |last=Valentine |first=James W. |year=2004 |publisher=University of Chicago Press |location=Chicago |isbn=978-0-226-84548-7 }}</ref>

{{Anchor|apical}}
[[Image:Venus Flower Basket (sponge-labelled).JPG|thumb|right|A cluster of ''Euplectella aspergillum'' sponges (Venus flower baskets), showing the apical–basal axes]]

Organisms that are attached to a [[Biology:Substrate|substrate]], such as [[Biology:Porifera|sponges]], animal-like protists also have distinctive ends. The part of the organism attached to the substrate is usually referred to as the '''basal end''' ({{ety|la|basis|support/foundation}}), whereas the end furthest from the attachment is referred to as the '''apical end''' ({{ety|la|apex|peak/tip}}).

===Radially symmetrical organisms===
Radially symmetrical organisms include those in the group [[Biology:Radiata|Radiata]]{{snd}} primarily [[Biology:Cnidaria|jellyfish, sea anemones and corals]] and the [[Biology:Ctenophora|comb jellies]].<ref name="Hickman et al. 2003" /><ref name="Ruppert2004" /> Adult [[Biology:Echinodermata|echinoderms]], such as [[Biology:Starfish|starfish]], [[Biology:Sea urchin|sea urchin]]s, [[Biology:Sea cucumber|sea cucumber]]s and others are also included, since they are pentaradial, meaning they have five [[Rotational symmetry#n-fold rotational symmetry|discrete rotational]] symmetry. Echinoderm [[Biology:Larva|larva]]e are not included, since they are [[Biology:Symmetry in biology|bilaterally symmetrical]].<ref name="Hickman et al. 2003" /><ref name="Ruppert2004" /> Radially symmetrical organisms always have one distinctive axis.

[[Biology:Cnidaria|Cnidaria]]ns (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).<ref name="Ruppert2004" /> For this reason, the end of the organism with the mouth is referred to as the '''oral end''' ({{ety|la|ōrālis|of the mouth}}),{{sfn|Collins|2020|loc="oral", accessed 13 October 2020}} and the opposite surface is the '''aboral end''' ({{ety|la|ab-|away from}}).{{sfn|Merriam-Webster|2020|loc="aboral", accessed 13 October 2020}}

Unlike vertebrates, cnidarians have only a single distinctive axis. "Lateral", "dorsal", and "ventral" have no meaning in such organisms, and all can be replaced by the generic term '''peripheral''' ({{ety|grc|περιφέρεια|circumference}}). '''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 [[Biology:Ctenophora|comb jellies]] do have distinct "tentacular" and "pharyngeal" axes<ref name="Oliveira2007">{{cite web |last1=Oliveira |first1=Otto Müller Patrão de |title=Chave de identificação dos Ctenophora da costa brasileira |url=https://www.researchgate.net/figure/Symmetry-planes-of-the-ctenophores-using-Bolinopsis-vitrea-as-model-a-view-of-the_fig1_247853778 |publisher=Biota Neotropica |access-date=6 April 2023 |ref=Oliveira2007}}</ref><ref>Ruppert et al. (2004), p. 184.</ref> and are thus anatomically equivalent to [[Biology:Bilateria|bilaterally symmetrical]] animals.

<gallery widths="220" heights="110">
Image:Radiate Radial Axes.JPG|''Aurelia aurita'', another species of [[Biology:Jellyfish|jellyfish]], showing multiple radial and medio-peripheral axes
File:Porania_pulvillus.jpg|The sea star ''[[Biology:Porania pulvillus|Porania pulvillus]]'', aboral and oral surfaces
</gallery>
{{clear}}

===Spiders===

Special terms are used for spiders. Two specialized terms are useful in describing views of [[Biology:Arachnid|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.<ref name="Kaston1972">{{cite book|last=Kaston|first=B.J.|title=How to Know the Spiders|edition=3rd|year=1972|page=19|publisher=W.C. Brown Co.|location=Dubuque, IA|isbn=978-0-697-04899-8 |oclc=668250654 }}</ref> Most spiders have eight eyes in four pairs. All the eyes are on the [[Biology:Carapace|carapace]] of the prosoma, and their sizes, shapes and locations are characteristic of various spider families and other [[Biology:Taxon|taxa]].<ref name=FOELIX2011>{{cite book|last1=Foelix|first1=Rainer|title=Biology of Spiders|date=2011|publisher=Oxford University Press, US|isbn=978-0-19-973482-5|pages=17–19|url=https://books.google.com/books?id=eOUVDAAAQBAJ&q=arachnid+anatomy|ref=Foelix2011|language=en}}</ref> Usually, the eyes are arranged in two roughly parallel, horizontal and symmetrical rows of eyes.{{r|FOELIX2011}} 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).{{r|FOELIX2011}}

<gallery>
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 [[Biology:Sparassidae|Sparassidae]].
File:Hogna species female Lycosidae showing eye pattern EOS 027s.jpg|Typical arrangement of eyes in the [[Biology:Lycosidae|Lycosidae]], with PME being the largest
File:Salticidae Male Anterior annotated.jpg|In the [[Biology:Salticidae|Salticidae]] the AME are the largest
</gallery>

==See also==
* [[Chirality]]
* [[Geometric terms of location]]
* [[Physics:Handedness|Handedness]]
* [[Biology:Laterality|Laterality]]
* [[Proper right and proper left]]
* [[Reflection symmetry]]
* [[Sinistral and dextral]]

==References==
=== Citations ===
{{Reflist|2}}

=== General sources ===
{{Refbegin}}
* {{cite web |title=Collins Online Dictionary {{!}} Definitions, Thesaurus and Translations |url=https://www.collinsdictionary.com |website=collinsdictionary.com |language=en|ref={{harvid|Collins|2020}}}}
* {{cite book |last1=Dyce |first1=KM |last2=Sack |first2=WO |last3=Wensing |first3=CJG |title=Textbook of veterinary anatomy |date=2010 |publisher=Saunders/Elsevier |location=St. Louis, Missouri |isbn=9781416066071 |edition=4th}}
* {{cite web|title=GeneOntology|url=http://amigo.geneontology.org|website=GeneOntology|publisher=The Gene Ontology Consortium|access-date=26 October 2014
| ref ={{harvid|GO|2014}} }}
* {{Cite book|title=Gray's anatomy: the anatomical basis of clinical practice |publisher=Elsevier Limited |editor-last=Standring |editor-first=Susan|isbn=9780702052309|edition=41st|location=Philadelphia|oclc=920806541|year=2016|ref={{harvid|Gray's Anatomy|2016}}}}
* {{cite book |last1=Kardong |first1=Kenneth |title=Vertebrates: comparative anatomy, function, evolution |year=2019 |publisher=McGraw-Hill |location=New York |isbn=9781260092042 |edition=8th|ref={{harvid|Kardong's|2019}}}}
* {{cite web |title=Dictionary by Merriam-Webster: America's most-trusted online dictionary |url=https://www.merriam-webster.com/dictionary/ |website=www.merriam-webster.com |language=en|ref={{harvid|Merriam-Webster|2020}}}}
* {{cite book|editor-last=Wake|editor-first=Marvale H.|title=Hyman's comparative vertebrate anatomy.|date=1992|publisher=University of Chicago Press|location=Chicago|isbn=9780226870113|edition=3rd|url-access=registration|url=https://archive.org/details/hymanscomparativ0000hyma}}
{{Refend}}


{{DEFAULTSORT:Anatomical Terms Of Location}}
[[Category:Anatomy| ]]
[[Category:Animal anatomy]]
[[Category:Medical terminology]]
[[Category:Orientation (geometry)]]

{{Sourceattribution|Anatomical terms of location}}