Standard anatomical terms of location are used to describe unambiguously the
anatomy of
human
Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
s and other
animal
Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...
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 by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
or
Greek roots, describe something in its
standard anatomical position. This position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. As part of defining and describing terms, the body is described through the use of
anatomical planes and
axes.
The meaning of terms that are used can change depending on whether a
vertebrate
Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain.
The vertebrates make up the subphylum Vertebra ...
is a
biped or a
quadruped, due to the difference in the
neuraxis, or if an
invertebrate is a
non-bilaterian. A non-bilaterian has no anterior or posterior surface for example but can still have a descriptor used such as
proximal or
distal in relation to a body part that is nearest to, or furthest from its middle.
International organisations have determined vocabularies that are often used as standards for subdisciplines of anatomy. For example, ''
Terminologia Anatomica'', ''Terminologia Neuroanatomica'', and ''
Terminologia Embryologica'' for humans and ''
Nomina Anatomica Veterinaria'' for animals. These allow parties that use anatomical terms, such as
anatomists,
veterinarians, and
medical doctors, to have a standard set of terms to communicate clearly the position of a structure.
Introduction

Standard
anatomical terms of location have been developed, usually based on Latin and Greek words, to enable all biological and medical scientists,
veterinarians,
medical doctors and
anatomists to precisely delineate and communicate information about animal bodies and their organs, even though the meaning of some of the terms often is context-sensitive.
Much of this information has been standardised in internationally agreed vocabularies for humans (''
Terminologia Anatomica'', ''Terminologia Neuroanatomica'', and ''
Terminologia Embryologica''),
with ''
Nomina Anatomica Veterinaria'' and ''Nomina Embryologica Veterinaria'' used for
animal anatomy.
Different terms are used for those
vertebrate
Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain.
The vertebrates make up the subphylum Vertebra ...
s that are
bipedal and those that are
quadripedal.
The reasoning is that the
neuraxis, and therefore the
standard anatomical position is different between the two groups.
Unique terms are also used to describe
invertebrates, because of their wider variety of shapes and
symmetries.
Standard anatomical position

Because
animal
Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...
s can change orientation with respect to their environment, and because
appendages like
limbs and
tentacles can change position with respect to the main body, terms to describe position need to refer to an animal when it is in its
standard anatomical position, even when its appendages are in another position. This helps to avoid confusion in terminology when referring to the same animal in different postures.
In humans, this refers to the body in a standing position with arms at the side and palms facing forward.
In
quadrupeds this is an animal standing upright with all four feet on the ground and the head facing forward. For a
fish this is belly down with neutral appendages.
Planes

Anatomical terms describe structures with relation to four main
anatomical planes.
Anatomical planes are useful in a number of fields including
medical imaging,
embryology, and the study of movement.
The four main planes are:
*The
median plane, also called the midsagittal plane, divides the body into left and right parts starting from the
sagittal suture.
The median plane passes through the head,
spinal cord,
navel and, in many animals, the tail.
*The
sagittal planes, also called the parasagittal planes or paramedian planes, are planes that are parallel to the median plane.
* The dorsal plane divides the body into dorsal (towards the backbone) and ventral (towards the belly) parts. In human anatomy
coronal plane is preferred, or sometimes the frontal plane, and the description may reference splitting the body into front and back parts
, but this phrasing is not as clear for animals with a horizontal spine like
quadrupeds or
fish.
* The
transverse plane
A transverse plane is a plane that is rotated 90° from two other planes.
Anatomy
The transverse plane is an anatomical plane that is perpendicular to the sagittal plane and the dorsal plane. It is also called the axial plane or horizonta ...
, also called the axial plane or horizontal plane, is perpendicular to the other two planes.
In an animal with a vertical craniocaudal axis, like a human, this plane is parallel to the ground; in an animal with a horizontal craniocaudal axis, like a quadruped, the coronal plane divides the animal into anterior and posterior sections.
Sagittal planes and transverse planes are used as
anatomical lines to delineate
bodily regions. There are several transverse planes with clinical relevance in the division of the torso into sections. They include the
transpyloric plane, the
subcostal plane, and the
transumbilical plane.
Axes

The three
axes of a vertebrate, are formed in
embryonic development
In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm, sperm cell (spermat ...
before and during the
gastrulation stage.
Distinct ends of the embryo are chosen, and the axis is named according to those directions. The three main axes of a
bilaterally symmetrical animal that intersect at right angles, are the left-right, the craniocaudal, and the anteroposterior axes.
* The left-right axis, also known as the horizontal or frontal axis
* The craniocaudal axis, also known as the rostrocaudal, longitudinal or cephalocaudal
* The anteroposterior axis, also known as the dorsoventral, or sagittal axis
An organism that is round, or
asymmetrical may have different axes.
Main terms
Superior and inferior
In the
standard human anatomical position, superior () or cranial, describes something that is nearer to the head, and inferior () or caudal describes what is below, and nearer to the feet.
Examples are the
superior mediastinum, and
inferior mediastinum. Neuroanatomy examples are the
superior colliculus, and the
inferior colliculus.
In veterinary anatomy, the terms superior and inferior are not used except to describe the eye, eyelids, lips and inner ear, using instead dorsal and ventral.
Anterior and posterior
Anterior () describes what is in front, and posterior () describes what is to the back of something.
For example, for many
fish the
gill openings are posterior to the eyes and anterior to the tail.
Dorsal and ventral
These two terms, used in
veterinary anatomy, are also used in
human anatomy mostly in
neuroanatomy, and
embryology, to describe something at the back (dorsal, posterior) or front (ventral, anterior) of an organ, or organism.
The dorsal () surface, (also dorsum) of an organism or
organ, refers to the back, or upper side, such as in the human, the dorsum of the
tongue, the
dorsum of the hand, and the
dorsum of the foot. If talking about the skull, the dorsal side is the top.
The ventral () surface refers to the front, or lower side, of an organism, or organ such as the undersurface of the tongue.
In a
fish, the
dorsal fin is on the upper surface and its
ventral fins (pelvic fins) are on the belly or undersurface.
The terms are used in other contexts, for example in
dorsal and ventral gun turrets on a bomber aircraft.
Medial and lateral
These terms describe how close something is to the median plane.
Lateral () describes something to the sides of an animal, as in "left lateral" and "right lateral". Medial () describes structures close to the median plane, or closer to the median plane 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 human beings), from which the head, neck, limb (anatomy), limbs, tail an ...
. The
genitals are medial to the legs. Temporal has a similar meaning to lateral but is restricted to the head.
The terms "left" and "right", or
sinistral and dextral, refer to the halves of a bilaterally symmetrical body divided by the median plane.
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 means removal of
testes on both sides of the body.
* Unilateral () one-sided or single-sided: on one side of the body.
For example, unilateral deafness is hearing impairment in one ear.
Varus () and
valgus ( ) are terms used to describe angulation or bowing of a bone or joint within the coronal plane, where the distal portion deviates towards (varus) or away from (valgus) the midline.
Proximal and distal

The terms proximal () and distal () are used to describe parts of a feature that are close to or distant from the main mass of the body, respectively.
Thus the upper arm in humans is proximal and the hand is distal. The main mass is taken as the center, the
chest, or the
heart
The heart is a muscular Organ (biology), organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrie ...
.
"Proximal and distal" are frequently used when describing
appendages, such as
fins,
tentacles, and
limbs. Although the direction indicated by "proximal" and "distal" is always respectively towards or away from the point of attachment, a given structure can be either proximal or distal in relation to another point of reference. Thus the elbow is distal to a wound on the upper arm, but proximal to a wound on the lower arm.
This terminology is also employed in molecular biology and therefore by extension is also used in chemistry, specifically referring to the atomic loci of molecules from the overall
moiety of a given compound.
Rostral, 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.
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 ] For example, in
horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...
s, the eyes are caudal to the nose and rostral to the back of the head.
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
gross anatomy and refers more to the front of the face than the superior aspect of the organism. But it is used in
embryology, and
neuroanatomy. Similarly, the term "caudal" is used more in embryology and neuroanatomy, and only occasionally in human gross anatomy.
The "rostrocaudal axis" refers to the curved line of the
neuraxis from the forehead (rostral) towards the tail end (caudal).
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 consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...
and the
peripheral nervous systems.
Central () describes something at, or close to the centre. For example, the
great vessels 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 (), Greek ...
) describes something that is situated nearer to the body's surface, such as a
peripheral nerve.
Superficial and deep
These terms refer to the distance of a structure from the surface.
Deep () describes something further away from the surface of the organism.
For example, the
external oblique muscle of the abdomen is deep to the skin. "Deep" is one of the few anatomical terms of location derived from
Old English
Old English ( or , or ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the Early Middle Ages. It developed from the languages brought to Great Britain by Anglo-S ...
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, the
epidermis is superficial to the
subcutis.
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 muscle), or to a named organ such as the
anterolateral tibial tubercle.
The term can also describe the direction and location of something that enters or courses through the body such as the
anterolateral system in the
spinal cord, and the
anterolateral central arteries. Another term anteromedial is used for example in the
anteromedial central arteries.
In the more internal
brain
The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...
and
spinal cord of the
central nervous system
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...
the terms
dorsal and ventral and their combinations are often used in place of anterior and posterior. In these organs numerous references need to be used, and in the brain for example the
prefrontal cortex has the divisions of the
dorsomedial prefrontal cortex, and the
dorsolateral prefrontal cortex. And the dorsomedial region has subcompartments that make use of other terms such as the
anterior cingulate cortex, and
infralimbic cortex. Structures such as the anterior cingulate cortex may be divided anatomically based on cognitive (
dorsal), and emotional (
ventral) components.
Proximodistal is the axis of an
appendage such as an arm or a leg, taken from its tip at the distal part to where it joins the body at the proximal part.
In
radiology
Radiology ( ) is the medical specialty that uses medical imaging to diagnose diseases and guide treatment within the bodies of humans and other animals. It began with radiography (which is why its name has a root referring to radiation), but tod ...
, various
X-ray views uses
terminology
Terminology is a group of specialized words and respective meanings in a particular field, and also the study of such terms and their use; the latter meaning is also known as terminology science. A ''term'' is a word, Compound (linguistics), com ...
based on where the X-ray beam enters and leaves the body, including the front to back view (anteroposterior), the back to front view (posteroanterior), and the side view (lateral). Combined terms were once generally hyphenated, but typically the hyphen is omitted.
Modifiers

Several terms are commonly seen and used as
prefixes:
* Sub- () is used to indicate something that is beneath, or something that is subordinate to or lesser than.
For example,
subcutaneous means beneath the skin.
* Hypo- () is used to indicate something that is beneath.
For example, the
hypoglossal nerve supplies the muscles beneath the tongue.
* Infra- () is used to indicate something that is within or below. For example, the
infraorbital nerve runs within the
orbit.
* Inter- () is used to indicate something that is between.
For example, the
intercostal muscles run between the
ribs.
* Super-'' or ''Supra- () is used to indicate something that is above something else.
For example, the
supraorbital ridges are above the
eyes.
* Ab- (), and ad- () are used to indicate that something is towards (ad-) or away from (ab-) something else.
For example
abduction and adduction refer to muscular movement away from, and towards the midline of the body, respectively.
Other terms are used as
suffixes, added to the end of words:
* -al () For example
femoral neck.
* -ad (), equivalent to '-ally', is a suffix createing the adverb form to indicate that something moves towards (-ad) something else.
For example, "distad" means "in the distal direction,"
as in "arterial blood flows distad/distally." Further examples may include cephalad (towards the cephalic end), orad, craniad, and proximad. The terms "proximally" and "distally" are in more common use in human and veterinary anatomic textbooks, while "proximad" and "distad," are used commonly in insect anatomy.
Other terms and special cases
Anatomical landmarks
The location of anatomical structures can also be described in relation to different
anatomical landmarks used in anatomy,
surface anatomy, surgery, and radiology.
Structures may be described as being at the level of a specific
vertebra, depending on the section of the
vertebral column
The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate. The spinal column is a segmente ...
the structure is at.
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
sacrum and coccyx are fused, they are not often used to provide the location.
References may also take origin from surface anatomy, 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
medial malleolus or the
medial epicondyle.
Anatomical lines are theoretical lines, using either horizontal transverse planes, or vertical sagittal planes, used to describe anatomical location. For examples, the mid-clavicular line is used as part of the
cardiac examination to feel the
apex beat of the
heart
The heart is a muscular Organ (biology), organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrie ...
, and the
axillary lines are reference lines for the
underarm region. Other types of lines in anatomy include the curved
nuchal lines on the
occipital bone
The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lob ...
, and the
gluteal lines on the
ilium.
Mouth and teeth
Special terms are used to describe the mouth and teeth.
Fields such as
osteology,
paleontology
Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure ge ...
and
dentistry
Dentistry, also known as dental medicine and oral medicine, is the branch of medicine focused on the Human tooth, teeth, gums, and Human mouth, mouth. It consists of the study, diagnosis, prevention, management, and treatment of diseases, dis ...
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" (or "mesial") are used for surfaces of individual teeth relative to the midpoint of the
dental arch, and "medial" and "lateral" are used in the standard sense relative to the median plane.
Terms used to describe structures include "buccal" () and "palatal" () referring to structures close to the
cheek and
hard palate respectively.
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 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 () is commonly used to describe the front of the hand, and dorsal is the back of the hand. The
palmar fascia is ''palmar'' to the
tendon
A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...
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
palm of the hand, and can also be used to refer to the
sole of the foot.
But ''palmar'' is used exclusively for the palm of the hand, and plantar is used exclusively for the sole of the foot.
Similarly, in the
limbs for clarity, the sides are named after the bones. In the
forearm, structures closer to the
radius
In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...
are radial, structures closer to the
ulna are ulnar, and structures relating to both bones are referred to as radioulnar, such as the
distal radioulnar joint.
Similarly, in the
lower leg, structures near the
tibia (shinbone) are tibial and structures near the
fibula are fibular (or peroneal).
Rotational direction
Anteversion and retroversion are complementary terms describing an anatomical structure that is rotated forwards (towards the front of the body) or backwards (towards the back of the body), relative to some other position. They are particularly used to describe the curvature of the
uterus
The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the hollow organ, organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic development, embryonic and prenatal development, f ...
.
* 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 ''uterus'', : uteri or uteruses) or womb () is the hollow organ, organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic development, embryonic and prenatal development, f ...
typically is anteverted, tilted slightly ''forward''. A misaligned
pelvis
The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...
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.
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,
serosa, or the cavity's wall).
* Terminal () at the extremity of a usually projecting structure; forming the end of a structure such as an
axon terminal.
* Visceral (): associated with the innermost layer of an
organ within the body. For example, the
visceral pleura covering the
lung
The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...
s, contrasted with the
parietal pleura lining the thoracic cavity.
* Parietal (): pertaining to the wall of a body cavity as the parietal pleura lining the thoracic cavity, contrasted with visceral pleura.
* Aboral (away from oral) is used to denote a location in an organism that is further from the mouth.
Other animals and organisms
Different terms are used because of different
body plans in animals, whether animals stand on two or four legs, and whether an animal is symmetrical or asymmetrical. For example, as humans are
bilaterally symmetrical, anatomical descriptions usually use the same terms as those for other vertebrates.
However, the standard human anatomical position means that their anterior/posterior and ventral/dorsal directions are the same, so the inferior/superior directions are used due to longstanding tradition instead of cranial/caudal, which apply regardless of position, as in other species.
The term "rostral" used to refer to the beak or nose in some animals is used less frequently in humans, with the exception of parts of the brain;
while humans do not have a visible tail (the
coccygeal vertebrae are present and commonly called the "tailbone") the term "caudal" that refers to the tail-end is also sometimes used in humans and animals without tails to refer to the hind part of the body.
Flounder and other flatfish which lie on the seabed on their left or right side are asymmetric, with both eyes on the 'up' side, making anatomical nomenclature a challenge.
Invertebrates have a large variety of body shapes that can present a problem when trying to apply standard directional terms. Depending on the organism, some terms are taken by analogy from vertebrate anatomy, and appropriate novel terms are applied as needed. Some such borrowed terms are widely applicable in most invertebrates; for example proximal, meaning "near" refers to the part of an appendage nearest to where it joins the body, and distal, meaning "standing away from" is used for the part furthest from the point of attachment. In all cases, the usage of terms is dependent on the body plan of the organism.
Direcoes anatomicas.svg, Anatomical terms of location in a dog
Anatomical-directions-kangaroo.svg, Anatomical terms of location in a kangaroo
Anatomical Directions and Axes.JPG, Anatomical terms of location in most fish
Horse Axes.JPG, Anatomical terms of location in a horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...
File:Pseudopleuronectes americanus.jpg, Flatfish are asymmetric, with both eyes lying on the same side of the head.
Non-bilaterian organisms
In
non-bilaterian organisms with a changeable shape, such as
amoeboid organisms, most directional terms are meaningless, since the shape of the organism is not constant and no distinct axes are fixed. Similarly, in
radially symmetrical organisms, there is nothing to distinguish one line through the centre of the organism from any other. An indefinite number of triads of mutually perpendicular axes could be defined, but any such choice of axes would be useless, as nothing would distinguish a chosen triad from any others. In such organisms, only terms such as ''superficial'' and ''deep'', or sometimes ''proximal'' and ''distal'', are usefully descriptive.
Elongated organisms
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
A protist ( ) or protoctist is any Eukaryote, eukaryotic organism that is not an animal, Embryophyte, land plant, or fungus. Protists do not form a Clade, natural group, or clade, but are a Paraphyly, paraphyletic grouping of all descendants o ...
, and are nearly always viewed on
microscope slides, where they appear essentially two-dimensional. In some cases a third axis can be defined, particularly where a non-terminal
cytostome
A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacu ...
or other unique structure is present.
Some elongated
protists
A protist ( ) or protoctist is any Eukaryote, eukaryotic organism that is not an animal, Embryophyte, land plant, or fungus. Protists do not form a Clade, natural group, or clade, but are a Paraphyly, paraphyletic grouping of all descendants o ...
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, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacu ...
in ''
Paramecium'' or ''
Stentor''), or the end that usually points in the direction of the organism's
locomotion (such as the end with the
flagellum in ''
Euglena''), is normally designated as the anterior end. The opposite end then becomes the posterior end.
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).
Organisms that are attached to a
substrate, such as
sponges and
animal-like protists also have distinctive ends. The part of the organism attached to the substrate is usually referred to as the basal end (), whereas the end furthest from the attachment is referred to as the apical end ().
Radially symmetrical organisms
Radially symmetrical organisms include those in the group
Radiata primarily
Cnidaria
Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...
ns (
jellyfish,
sea anemones and
corals, and the
comb jellies).
Adult
echinoderms, such as
starfish,
sea urchins,
sea cucumbers and others are also included, since they have a
pentamerous symmetry having five
discrete symmetric parts arranged around a central axis.
Echinoderm
larvae are not included, since they are
bilaterally symmetrical.
Cnidarians have an incomplete digestive system, meaning that one end of the organism has a mouth, the oral end (), and the opposite aboral end () has no opening from the gut (coelenteron).
They are radially symmetric around the oral-aboral axis.
Having only the single distinctive axis, "lateral", "dorsal", and "ventral" have no meaning, 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.
Comb jellies have a biradial symmetry about only two planes, a tentacular plane, and a pharyngeal plane.
Image:Radiate Radial Axes.JPG, '' Aurelia aurita'', another species of jellyfish, showing multiple radial and medio-peripheral axes
File:Porania_pulvillus.jpg, The sea star '' Porania pulvillus'', aboral and oral surfaces
Spiders
Special terms are used for
spiders. Two such terms are useful in describing views of the legs and
pedipalps of spiders, and other
arachnid
Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...
s. Prolateral refers to the surface of a leg that is closest to the anterior end of an arachnid's body. Retrolateral refers to the surface of a leg that is closest to the posterior end of an arachnid's body.
Most spiders have eight eyes in four pairs. All the eyes are on the
carapace of the
prosoma, and their sizes, shapes and locations are characteristic of various spider families and other
taxa.
Usually, the eyes are arranged in two roughly parallel, horizontal and symmetrical rows of eyes. Eyes are labelled according to their position as anterior and posterior lateral eyes (ALE) and (PLE); and anterior and posterior median eyes (AME) and (PME).
File:Palystes superciliosus male anterior 2012 03 04 3452.JPG, Aspects of spider anatomy. This aspect shows the mainly prolateral surface of the anterior femora, plus the typical horizontal eye pattern of the Sparassidae.
File:Hogna species female Lycosidae showing eye pattern EOS 027s.jpg, Typical arrangement of eyes in the Lycosidae, with PME being the largest
File:Salticidae Male Anterior annotated.jpg, In the Salticidae the AME are the largest.
See also
*
Chirality
*
Geometric terms of location
*
Reflection symmetry
References
{{DEFAULTSORT:Anatomical Terms Of Location
Animal anatomy
Medical terminology
Orientation (geometry)
Position