Anatomical terms of location

Standard anatomical terms of location are used to describe unambiguously the anatomy of animals, including humans.

The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position.

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.

[1] The reasoning is that the neuraxis is different between the two groups, and so is what is considered the standard anatomical position, such as how humans tend to be standing upright and with their arms reaching forward.

Unique terms are also used to describe invertebrates as well, because of their wider variety of shapes and symmetry.

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).

The same logic is applied to all planes of the body and, thus top-to-bottom or bottom-to-top X-ray projections are known as "superoinferior" and "inferosuperior," respectively.

[21] For example, in the anatomical position, the most superior part of the human body is the head and the most inferior is the feet.

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

[31] 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.

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

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

The terms are used in other contexts; for example dorsal and ventral gun turrets on a bomber aircraft.

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.

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

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

[2] Fields such as osteology, palaeontology and dentistry apply special terms of location to describe the mouth and teeth.

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

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

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

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

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

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

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

"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').

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

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

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

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.

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 .
A male and female human in the standard anatomical position
Anatomical terms can be combined to be more specific. This is a dorsolateral view of the frog Mantophryne insignis .
Anatomical planes in a human
Organisms where the ends of the long axis are distinct ( Paramecium caudatum , above, and Stentor roeselii , below).
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.
Anatomical directional reference
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.
Anatomical terms used to describe a human hand
Asymmetrical and spherical body shapes . (a) An organism with an asymmetrical, amoeboid body plan ( Amoeba proteus – an amoeba). (b) An organism with a spherical body plan ( Actinophrys sol – a heliozoan ).
Four individuals of Phaeodactylum tricornutum , a diatom with a fixed elongated shape
A cluster of Euplectella aspergillum sponges (Venus flower baskets) , showing the apical–basal axes