Anatomical terms of location

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Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Anatomical terms of location_sentence_0

Terms used generally derive from Latin or Greek roots and used to describe something in its standard anatomical position. Anatomical terms of location_sentence_1

This position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. Anatomical terms of location_sentence_2

As part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axes. Anatomical terms of location_sentence_3

The meaning of terms that are used can change depending on whether an organism is bipedal or quadrupedal. Anatomical terms of location_sentence_4

Additionally, for some animals such as invertebrates, some terms may not have any meaning at all; for example, an animal that is radially symmetrical will have no anterior surface, but can still have a description that a part is close to the middle ("proximal") or further from the middle ("distal"). Anatomical terms of location_sentence_5

International organisations have determined vocabularies that are often used as standard vocabularies for subdisciplines of anatomy, for example, Terminologia Anatomica for humans, and Nomina Anatomica Veterinaria for animals. Anatomical terms of location_sentence_6

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. Anatomical terms of location_sentence_7

Introduction Anatomical terms of location_section_0

Standard anatomical and zoological terms of location have been developed, usually based on Latin and Greek words, to enable all biological and medical scientists, veterinarians, doctors and anatomists to precisely delineate and communicate information about animal bodies and their organs, even though the meaning of some of the terms often is context-sensitive. Anatomical terms of location_sentence_8

Much of this information has been standardised in internationally agreed vocabularies for humans (Terminologia Anatomica) and animals (Nomina Anatomica Veterinaria). Anatomical terms of location_sentence_9

For humans, one type of vertebrate, and other animals that stand on two feet (bipeds), terms that are used are different from those that stand on four (quadrupeds). Anatomical terms of location_sentence_10

One reason is that humans have a different neuraxis and another is that unlike animals that rest on four limbs, humans are considered when describing anatomy as being in the standard anatomical position, which is standing up with arms outstretched. Anatomical terms of location_sentence_11

Thus, what is on "top" of a human is the head, whereas the "top" of a dog may be its back, and the "top" of a flounder could refer to either its left or its right side. Anatomical terms of location_sentence_12

Unique terms are used to describe animals without a backbone (invertebrates), because of their wide variety of shapes and symmetry. Anatomical terms of location_sentence_13

Standard anatomical position Anatomical terms of location_section_1

Main article: Standard anatomical position Anatomical terms of location_sentence_14

Because animals can change orientation with respect to their environment, and because appendages like limbs and tentacles can change position with respect to the main body, terms to describe position need to refer to an animal when it is in its standard anatomical position. Anatomical terms of location_sentence_15

This means descriptions as if the organism is in its standard anatomical position, even when the organism in question has appendages in another position. Anatomical terms of location_sentence_16

This helps avoid confusion in terminology when referring to the same organism in different postures. Anatomical terms of location_sentence_17

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. Anatomical terms of location_sentence_18

Combined terms Anatomical terms of location_section_2

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. Anatomical terms of location_sentence_19

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). Anatomical terms of location_sentence_20

In radiology, an X-ray image may be said to be "anteroposterior", indicating that the beam of X-rays passes from their source to patient's anterior body wall through the body to exit through posterior body wall. Anatomical terms of location_sentence_21

Combined terms were once generally, hyphenated, but the modern tendency is to omit the hyphen. Anatomical terms of location_sentence_22

Planes Anatomical terms of location_section_3

Main article: Anatomical plane Anatomical terms of location_sentence_23

Anatomical terms describe structures with relation to four main anatomical planes: Anatomical terms of location_sentence_24

Anatomical terms of location_ordered_list_0

  1. The median plane, which divides the body into left and right. This passes through the head, spinal cord, navel, and, in many animals, the tail.Anatomical terms of location_item_0_0
  2. The sagittal planes, which are to the median plane.Anatomical terms of location_item_0_1
  3. The frontal plane, also called the coronal plane, which divides the body into front and back.Anatomical terms of location_item_0_2
  4. The horizontal plane, also known as the transverse plane, which is perpendicular to the other two planes. In a human, this plane is parallel to the ground; in a quadruped, this divides the animal into anterior and posterior sections.Anatomical terms of location_item_0_3

Axes Anatomical terms of location_section_4

The axes of the body are lines drawn about which an organism is roughly symmetrical. Anatomical terms of location_sentence_25

To do this, distinct ends of an organism are chosen, and the axis is named according to those directions. Anatomical terms of location_sentence_26

An organism that is symmetrical on both sides has three main axes that intersect at right angles. Anatomical terms of location_sentence_27

An organism that is round or not symmetrical may have different axes. Anatomical terms of location_sentence_28

Example axes are: Anatomical terms of location_sentence_29

Anatomical terms of location_unordered_list_1

  • The anteroposterior axisAnatomical terms of location_item_1_4
  • The cephalocaudal axisAnatomical terms of location_item_1_5
  • The dorsoventral axisAnatomical terms of location_item_1_6

Examples of axes in specific animals are shown below. Anatomical terms of location_sentence_30

Anatomical terms of location_unordered_list_2

  • Anatomical terms of location_item_2_7
  • Anatomical terms of location_item_2_8
  • Anatomical terms of location_item_2_9

Modifiers Anatomical terms of location_section_5

Several terms are commonly seen and used as prefixes: Anatomical terms of location_sentence_31

Anatomical terms of location_unordered_list_3

  • Sub- (from Latin sub 'preposition beneath, close to, nearly etc') is used to indicate something that is beneath, or something that is subordinate to or lesser than. For example, subcutaneous means beneath the skin, and "subglobular" may mean smaller than aAnatomical terms of location_item_3_10
  • Hypo- (from Ancient Greek ὑπό 'under') is used to indicate something that is beneath. For example, the hypoglossal nerve supplies the muscles beneath the tongue.Anatomical terms of location_item_3_11
  • Infra- (from Latin infra 'under') is used to indicate something that is within or below. For example, the infraorbital nerve runs within the orbit.Anatomical terms of location_item_3_12
  • Inter- (from Latin inter 'between') is used to indicate something that is between. For example, the intercostal muscles run between the ribs.Anatomical terms of location_item_3_13
  • Super- or Supra- (from Latin super, supra 'above, on top of') is used to indicate something that is above something else. For example, the supraorbital ridges are above the eyes.Anatomical terms of location_item_3_14

Other terms are used as suffixes, added to the end of words: Anatomical terms of location_sentence_32

Anatomical terms of location_unordered_list_4

  • -ad (from Latin ad 'towards') and ab- (from Latin ab) are used to indicate that something is towards (-ad) or away from (-ab) something else. For example, "distad" means "in the distal direction", and "distad of the femur" means "beyond the femur in the distal direction". Further examples may include cephalad (towards the cephalic end), craniad, and distad.Anatomical terms of location_item_4_15

Main terms Anatomical terms of location_section_6

Superior and inferior Anatomical terms of location_section_7

Superior (from Latin super 'above') describes what is above something and inferior (from Latin inferus 'below') describes what is below it. Anatomical terms of location_sentence_33

For example, in the anatomical position, the most superior part of the human body is the head and the most inferior is the feet. Anatomical terms of location_sentence_34

As a second example, in humans, the neck is superior to the chest but inferior to the head. Anatomical terms of location_sentence_35

Anterior and posterior Anatomical terms of location_section_8

"Anterior" redirects here. Anatomical terms of location_sentence_36

For other uses, see Anterior (disambiguation). Anatomical terms of location_sentence_37

Anterior (from Latin ante 'before') describes what is in front, and posterior (from Latin post 'after') describes what is to the back of something. Anatomical terms of location_sentence_38

For example, in a dog the nose is anterior to the eyes and the tail is considered the most posterior part; in many fish the gill openings are posterior to the eyes but anterior to the tail. Anatomical terms of location_sentence_39

Medial and lateral Anatomical terms of location_section_9

These terms describe how close something is to the midline, or the medial plane. Anatomical terms of location_sentence_40

Lateral (from Latin lateralis 'to the side') describes something to the sides of an animal, as in "left lateral" and "right lateral". Anatomical terms of location_sentence_41

Medial (from Latin medius 'middle') describes structures close to the midline, or closer to the midline than another structure. Anatomical terms of location_sentence_42

For example, in a human, the arms are lateral to the torso. Anatomical terms of location_sentence_43

The genitals are medial to the legs. Anatomical terms of location_sentence_44

The terms "left" and "right" are sometimes used, or their Latin alternatives (Latin: dexter, lit. Anatomical terms of location_sentence_45

'right'; Latin: sinister, lit. Anatomical terms of location_sentence_46

'left'). Anatomical terms of location_sentence_47

However, as left and right sides are mirror images, using these words is somewhat confusing, as structures are duplicated on both sides. Anatomical terms of location_sentence_48

For example, it is very confusing to say the dorsal fin of a dolphin is "right of" the left pectoral fin, but is "left of" the right eye, but much easier and clearer to say "the dorsal fin is medial to the pectoral fins". Anatomical terms of location_sentence_49

Terms derived from lateral include: Anatomical terms of location_sentence_50

Anatomical terms of location_unordered_list_5

  • Contralateral (from Latin contra 'against'): on the side opposite to another structure. For example, the right arm and leg are controlled by the left, contralateral, side of the brain.Anatomical terms of location_item_5_16
  • Ipsilateral (from Latin ipse 'same'): on the same side as another structure. For example, the left arm is ipsilateral to the left leg.Anatomical terms of location_item_5_17
  • Bilateral (from Latin bis 'twice'): on both sides of the body. For example, bilateral orchiectomy means removal of testes on both sides of the body.Anatomical terms of location_item_5_18
  • Unilateral (from Latin unus 'one'): on one side of the body. For example, a stroke can result in unilateral weakness, meaning weakness on one side of the body.Anatomical terms of location_item_5_19

Varus (from Latin 'knock-kneed') and valgus (from Latin 'bow-legged') are terms used to describe a state in which a part further away is abnormally placed towards (varus) or away from (valgus) the midline. Anatomical terms of location_sentence_51

Proximal and distal Anatomical terms of location_section_10

"Proximal" and "distal" redirect here. Anatomical terms of location_sentence_52

For the linguistic terms, see Demonstrative § Distal and proximal demonstratives. Anatomical terms of location_sentence_53

For the dental terms, see Glossary of dentistry. Anatomical terms of location_sentence_54

The terms proximal (from Latin proximus 'nearest') and distal (from Latin distare 'to stand away from') are used to describe parts of a feature that are close to or distant from the main mass of the body, respectively. Anatomical terms of location_sentence_55

Thus the upper arm in humans is proximal and the hand is distal. Anatomical terms of location_sentence_56

"Proximal and distal" are frequently used when describing appendages, such as fins, tentacles, and limbs. Anatomical terms of location_sentence_57

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. Anatomical terms of location_sentence_58

Thus the elbow is distal to a wound on the upper arm, but proximal to a wound on the lower arm. Anatomical terms of location_sentence_59

This terminology is also employed in molecular biology and therefore by extension is also used in chemistry, specifically referring to the atomic loci of molecules from the overall moiety of a given compound. Anatomical terms of location_sentence_60

Central and peripheral Anatomical terms of location_section_11

Central and peripheral refer to the distance towards and away from the centre of something. Anatomical terms of location_sentence_61

That might be an organ, a region in the body, or an anatomical structure. Anatomical terms of location_sentence_62

For example, the Central nervous system and the peripheral nervous systems. Anatomical terms of location_sentence_63

Central (from Latin centralis) describes something close to the centre. Anatomical terms of location_sentence_64

For example, the great vessels run centrally through the body; many smaller vessels branch from these. Anatomical terms of location_sentence_65

Peripheral (from Latin peripheria, originally from Ancient Greek) describes something further away from the centre of something. Anatomical terms of location_sentence_66

For example, the arm is peripheral to the body. Anatomical terms of location_sentence_67

Superficial and deep Anatomical terms of location_section_12

These terms refer to the distance of a structure from the surface. Anatomical terms of location_sentence_68

Deep (from Old English) describes something further away from the surface of the organism. Anatomical terms of location_sentence_69

For example, the external oblique muscle of the abdomen is deep to the skin. Anatomical terms of location_sentence_70

"Deep" is one of the few anatomical terms of location derived from Old English rather than Latin – the anglicised Latin term would have been "profound" (from Latin profundus 'due to depth'). Anatomical terms of location_sentence_71

Superficial (from Latin superficies 'surface') describes something near the outer surface of the organism. Anatomical terms of location_sentence_72

For example, in skin, the epidermis is superficial to the subcutis. Anatomical terms of location_sentence_73

Dorsal and ventral Anatomical terms of location_section_13

These two terms, used in anatomy and embryology, describe something at the back (dorsal) or front/belly (ventral) of an organism. Anatomical terms of location_sentence_74

The dorsal (from Latin dorsum 'back') surface of an organism refers to the back, or upper side, of an organism. Anatomical terms of location_sentence_75

If talking about the skull, the dorsal side is the top. Anatomical terms of location_sentence_76

The ventral (from Latin venter 'belly') surface refers to the front, or lower side, of an organism. Anatomical terms of location_sentence_77

For example, in a fish, the pectoral fins are dorsal to the anal fin, but ventral to the dorsal fin. Anatomical terms of location_sentence_78

Cranial and caudal Anatomical terms of location_section_14

Specific terms exist to describe how close or far something is to the head or tail of an animal. Anatomical terms of location_sentence_79

To describe how close to the head of an animal something is, three distinct terms are used: Anatomical terms of location_sentence_80

Anatomical terms of location_unordered_list_6

  • Rostral (from Latin 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.Anatomical terms of location_item_6_20
  • Cranial (from Greek κρανίον 'skull') or cephalic (from Greek κεφαλή 'head') describes how close something is to the head of an organism.Anatomical terms of location_item_6_21
  • Caudal (from Latin cauda 'tail') describes how close something is to the trailing end of an organism.Anatomical terms of location_item_6_22

For example, in horses, the eyes are caudal to the nose and rostral to the back of the head. Anatomical terms of location_sentence_81

These terms are generally preferred in veterinary medicine and not used as often in human medicine. Anatomical terms of location_sentence_82

In humans, "cranial" and "cephalic" are used to refer to the skull, with "cranial" being used more commonly. Anatomical terms of location_sentence_83

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. Anatomical terms of location_sentence_84

Similarly, the term "caudal" is used more in embryology and only occasionally used in human anatomy. Anatomical terms of location_sentence_85

This is because the brain is situated at the superior part of the head whereas the nose is situated in the anterior part. Anatomical terms of location_sentence_86

Thus, the "rostrocaudal axis" refers to a C shape (see image). Anatomical terms of location_sentence_87

Other terms and special cases Anatomical terms of location_section_15

Anatomical landmarks Anatomical terms of location_section_16

The location of anatomical structures can also be described in relation to different anatomical landmarks. Anatomical terms of location_sentence_88

They are used in anatomy, surface anatomy, surgery, and radiology. Anatomical terms of location_sentence_89

Structures may be described as being at the level of a specific spinal vertebra, depending on the section of the vertebral column the structure is at. Anatomical terms of location_sentence_90

The position is often abbreviated. Anatomical terms of location_sentence_91

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". Anatomical terms of location_sentence_92

Because the sacrum and coccyx are fused, they are not often used to provide the location. Anatomical terms of location_sentence_93

References may also take origin from superficial anatomy, made to landmarks that are on the skin or visible underneath. Anatomical terms of location_sentence_94

For example, structures may be described relative to the anterior superior iliac spine, the medial malleolus or the medial epicondyle. Anatomical terms of location_sentence_95

Anatomical lines are used to describe anatomical location. Anatomical terms of location_sentence_96

For example, the mid-clavicular line is used as part of the cardiac exam in medicine to feel the apex beat of the heart. Anatomical terms of location_sentence_97

Mouth and teeth Anatomical terms of location_section_17

Main article: Dental terminology Anatomical terms of location_sentence_98

Special terms are used to describe the mouth and teeth. Anatomical terms of location_sentence_99

Fields such as osteology, palaeontology and dentistry apply special terms of location to describe the mouth and teeth. Anatomical terms of location_sentence_100

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. Anatomical terms of location_sentence_101

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. Anatomical terms of location_sentence_102

Terms used to describe structures include "buccal" (from Latin bucca 'cheek') and "palatal" (from Latin) referring to structures close to the cheek and hard palate respectively. Anatomical terms of location_sentence_103

Hands and feet Anatomical terms of location_section_18

Several anatomical terms are particular to the hands and feet. Anatomical terms of location_sentence_104

For improved clarity, the directional term palmar (from Latin palma 'palm of the hand') is usually used to describe the front of the hand, and dorsal is the back of the hand. Anatomical terms of location_sentence_105

For example, the top of a dog's paw is its dorsal surface; the underside, either the palmar (on the forelimb) or the plantar (on the hindlimb) surface. Anatomical terms of location_sentence_106

The palmar fascia is palmar to the tendons of muscles which flex the fingers, and the dorsal venous arch is so named because it is on the dorsal side of the foot. Anatomical terms of location_sentence_107

Volar can also be used to refer to the underside of the palm or sole, which are themselves also sometimes used to describe location as and . Anatomical terms of location_sentence_108

For example, volar pads are those on the underside of hands, fingers, feet, and toes. Anatomical terms of location_sentence_109

These terms are used to avoid confusion when describing the median surface of the hand and what is the "anterior" or "posterior" surface – "anterior" can be used to describe the palm of the hand, and "posterior" can be used to describe the back of the hand and arm. Anatomical terms of location_sentence_110

This confusion can arise because the forearm can pronate and supinate. Anatomical terms of location_sentence_111

Similarly, in the forearm, for clarity, the sides are named after the bones. Anatomical terms of location_sentence_112

Structures closer to the radius are radial, structures closer to the ulna are ulnar, and structures relating to both bones are referred to as radioulnar. Anatomical terms of location_sentence_113

Similarly, in the lower leg, structures near the tibia (shinbone) are tibial and structures near the fibula are fibular (or peroneal). Anatomical terms of location_sentence_114

Rotational direction Anatomical terms of location_section_19

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. Anatomical terms of location_sentence_115

They are particularly used to describe the curvature of the uterus. Anatomical terms of location_sentence_116

Anatomical terms of location_unordered_list_7

  • Anteversion (from Latin anteversus) describes an anatomical structure being tilted further forward than normal, whether pathologically or incidentally. For example, a woman's uterus typically is anteverted, tilted slightly forward. A misaligned pelvis may be anteverted, that is to say tilted forward to some relevant degree.Anatomical terms of location_item_7_23
  • Retroversion (from Latin retroversus) describes an anatomical structure tilted back away from something. An example is a retroverted uterus.Anatomical terms of location_item_7_24

Other directional terms Anatomical terms of location_section_20

Several other terms are also used to describe location. Anatomical terms of location_sentence_117

These terms are not used to form the fixed axes. Anatomical terms of location_sentence_118

Terms include: Anatomical terms of location_sentence_119

Anatomical terms of location_unordered_list_8

  • Axial (from Latin 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, respectivelyAnatomical terms of location_item_8_25
  • Luminal (from Latin lumen 'light, opening'): on the—hollow—inside of an organ's lumen (body cavity or tubular structure); adluminal is towards, abluminal is away from the lumen. Opposite to outermost (the adventitia, serosa, or the cavity's wall).Anatomical terms of location_item_8_26
  • Parietal (from Latin paries 'wall'): pertaining to the wall of a body cavity. For example, the parietal peritoneum is the lining on the inside of the abdominal cavity. Parietal can also refer specifically to the parietal bone of the skull or associated structures.Anatomical terms of location_item_8_27
  • Terminal (from Latin terminus 'boundary or end') at the extremity of a usually projecting structure. For example, " antenna with a terminal sensory hair".Anatomical terms of location_item_8_28
  • Visceral and viscus (from Latin viscera 'internal organs'): associated with organs within the body's cavities. For example, the stomach is covered with a lining called the visceral 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.Anatomical terms of location_item_8_29
  • Aboral (opposite to oral) is used to denote a location along the gastrointestinal canal that is relatively closer to the anus.Anatomical terms of location_item_8_30

Specific animals and other organisms Anatomical terms of location_section_21

Different terms are used because of different body plans in animals, whether animals stand on one or two legs, and whether an animal is symmetrical or not, as discussed above. Anatomical terms of location_sentence_120

For example, as humans are approximately bilaterally symmetrical organisms, anatomical descriptions usually use the same terms as those for other vertebrates. Anatomical terms of location_sentence_121

However, humans stand upright on two legs, meaning their anterior/posterior and dorsal/ventral directions the same, and the inferior/superior directions necessary. Anatomical terms of location_sentence_122

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; 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. Anatomical terms of location_sentence_123

In invertebrates, the large variety of body shapes presents a difficult problem when attempting to apply standard directional terms. Anatomical terms of location_sentence_124

Depending on the organism, some terms are taken by analogy from vertebrate anatomy, and appropriate novel terms are applied as needed. Anatomical terms of location_sentence_125

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. Anatomical terms of location_sentence_126

In all cases, the usage of terms is dependent on the body plan of the organism. Anatomical terms of location_sentence_127

Anatomical terms of location_unordered_list_9

  • Anatomical terms of location_item_9_31
  • Anatomical terms of location_item_9_32
  • Anatomical terms of location_item_9_33
  • Anatomical terms of location_item_9_34

Asymmetrical and spherical organisms Anatomical terms of location_section_22

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. Anatomical terms of location_sentence_128

Similarly, in spherically symmetrical organisms, there is nothing to distinguish one line through the centre of the organism from any other. Anatomical terms of location_sentence_129

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. Anatomical terms of location_sentence_130

In such organisms, only terms such as superficial and deep, or sometimes proximal and distal, are usefully descriptive. Anatomical terms of location_sentence_131

Elongated organisms Anatomical terms of location_section_23

In organisms that maintain a constant shape and have one dimension longer than the other, at least two directional terms can be used. Anatomical terms of location_sentence_132

The long or longitudinal axis is defined by points at the opposite ends of the organism. Anatomical terms of location_sentence_133

Similarly, a perpendicular transverse axis can be defined by points on opposite sides of the organism. Anatomical terms of location_sentence_134

There is typically no basis for the definition of a third axis. Anatomical terms of location_sentence_135

Usually such organisms are planktonic (free-swimming) protists, and are nearly always viewed on microscope slides, where they appear essentially two-dimensional. Anatomical terms of location_sentence_136

In some cases a third axis can be defined, particularly where a non-terminal cytostome or other unique structure is present. Anatomical terms of location_sentence_137

Some elongated protists have distinctive ends of the body. Anatomical terms of location_sentence_138

In such organisms, the end with a mouth (or equivalent structure, such as the cytostome in Paramecium or Stentor), or the end that usually points in the direction of the organism's locomotion (such as the end with the flagellum in Euglena), is normally designated as the anterior end. Anatomical terms of location_sentence_139

The opposite end then becomes the posterior end. Anatomical terms of location_sentence_140

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). Anatomical terms of location_sentence_141

Organisms that are attached to a substrate, such as sponges, animal-like protists also have distinctive ends. Anatomical terms of location_sentence_142

The part of the organism attached to the substrate is usually referred to as the basal end (from Latin basis 'support/foundation'), whereas the end furthest from the attachment is referred to as the apical end (from Latin apex 'peak/tip'). Anatomical terms of location_sentence_143

Radially symmetrical organisms Anatomical terms of location_section_24

Radially symmetrical organisms include those in the group Radiata – primarily jellyfish, sea anemones and corals and the comb jellies. Anatomical terms of location_sentence_144

Adult echinoderms, such as starfish, sea urchins, sea cucumbers and others are also included, since they are pentaradial, meaning they have five discrete rotational symmetry. Anatomical terms of location_sentence_145

Echinoderm larvae are not included, since they are bilaterally symmetrical. Anatomical terms of location_sentence_146

Radially symmetrical organisms always have one distinctive axis. Anatomical terms of location_sentence_147

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). Anatomical terms of location_sentence_148

For this reason, the end of the organism with the mouth is referred to as the oral end (from Latin ōrālis 'of the mouth'), and the opposite surface is the aboral end (from Latin ab- 'away from'). Anatomical terms of location_sentence_149

Unlike vertebrates, cnidarians have no other distinctive axes. Anatomical terms of location_sentence_150

"Lateral", "dorsal", and "ventral" have no meaning in such organisms, and all can be replaced by the generic term peripheral (from Ancient Greek περιφέρεια 'circumference'). Anatomical terms of location_sentence_151

Medial can be used, but in the case of radiates indicates the central point, rather than a central axis as in vertebrates. Anatomical terms of location_sentence_152

Thus, there are multiple possible radial axes and medio-peripheral (half-) axes. Anatomical terms of location_sentence_153

However, some biradially symmetrical comb jellies do have distinct "tentacular" and "pharyngeal" axes and are thus anatomically equivalent to bilaterally symmetrical animals. Anatomical terms of location_sentence_154

Anatomical terms of location_unordered_list_10

  • Anatomical terms of location_item_10_35
  • Anatomical terms of location_item_10_36

Spiders Anatomical terms of location_section_25

See also: Glossary of spider terms and Spider anatomy Anatomical terms of location_sentence_155

Special terms are used for spiders. Anatomical terms of location_sentence_156

Two specialized terms are useful in describing views of arachnid legs and pedipalps. Anatomical terms of location_sentence_157

Prolateral refers to the surface of a leg that is closest to the anterior end of an arachnid's body. Anatomical terms of location_sentence_158

Retrolateral refers to the surface of a leg that is closest to the posterior end of an arachnid's body. Anatomical terms of location_sentence_159

Most spiders have eight eyes in four pairs. Anatomical terms of location_sentence_160

All the eyes are on the carapace of the prosoma, and their sizes, shapes and locations are characteristic of various spider families and other taxa. Anatomical terms of location_sentence_161

Usually, the eyes are arranged in two roughly parallel, horizontal and symmetrical rows of eyes. Anatomical terms of location_sentence_162

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). Anatomical terms of location_sentence_163

Anatomical terms of location_unordered_list_11

  • Anatomical terms of location_item_11_37
  • Anatomical terms of location_item_11_38
  • Anatomical terms of location_item_11_39

See also Anatomical terms of location_section_26

Anatomical terms of location_unordered_list_12

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: terms of location.