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Two major problems arise with common usage, however. First, they tend to be language-specific, requiring translation into equivalent, or almost-equivalent, terms in other languages. They are not universal terms that may be readily understood by zoologists speaking other languages. Differences in terminology remain a problem that, to some extent, still separates the fields of zoological anatomy (sometimes called Zootomy ) and human (medical) Anatomy . The second, and larger, problem is caused by the very nature of animals. Most animals are capable of moving relative to their environment (see Fig. 1). So while "up" might refer to the top of someone's head when they are standing upright, the same term ("up") would describe their belly while they are lying down. Therefore, standardized anatomical (and zootomical) terms of location have been developed, usually based on Latin words, to enable all biological and medical scientists to precisely delineate and communicate information about animal (including human) bodies and their component organs. STANDARD ANATOMICAL POSITION Since Animal can change position with respect to their environment, and since any Appendages (arms, legs, tentacles, ''etc...'') can change position with respect to the main body, it is important that any descriptional terms refer to the Organism when it is in its standard anatomical position. Thus, and very importantly, ''all descriptions are with respect to the organism in its standard anatomical position'', even when the organism in question has appendages in another position. For example, see Fig. 8, where the tentacles are curved, and therefore not in anatomical position. However, a straight position is assumed when describing the Proximo-distal axis. This helps avoid confusion in terminology when referring to the same organism in different postures. Invertebrate and vertebrate zootomy There is no formal definition of standard anatomical position used in most Zoology . However, the position can be loosely defined as that position in which the organism will usually be found when at rest. Thus, for most Invertebrates , this would be the position in which they are normally found when not feeding, hiding, actively moving, and so on (see Figs. 6–9, below), and any Appendages are straight. For Bilaterally-symmetrical organisms, such Vertebrates or some invertebrates, this can be refined to include that the organisms are standing erect in a normal posture, and looking forward.Campbell and Reece (2005), ''p.'' 630. (For example, see Figs. 2–4, below.) Medical (human) anatomy Unlike the situation in zootomy, standard anatomical position is rigidly defined for human anatomy. As with other vertebrates, the human body is standing erect and at rest. Unlike the situation in other vertebrates, the limbs (arms and legs) are placed in unnatural positions reminiscent of the Supine Position adopted by Cadavers during autopsy. Therefore, the body has its feet together (or slightly separated), and its arms are rotated outward so that the Palms are forward, and the Thumbs are pointed away from the body (forearms supine). As well, the arms are usually moved slightly out from the body, so that the hands do not touch the sides.Marieb (1995), ''pp.'' 13–14.Tortora and Derrickson (2006), ''pp.'' 12–13 The positions of the limbs (and the arms in particular) have important implications for directional terms in those appendages. Skull In humans, the anatomical position of the Skull has been agreed by international convention to be the Frankfurt Plane , a position where the lower margins of the Orbits and the upper margins of the Ear Canal s all lie in the same horizontal plane. This is a good approximation to the position where the subject is standing upright and facing forwards. DIRECTIONAL TERMS Ultimately, the bodies we are most familiar with are vertebrate bodies similar to our own. All Vertebrates (including humans) have the same basic body plan (or Bauplan ) — they are Bilaterally Symmetrical . That is, they have mirror-image left and right halves if divided down the centre.Kardong (2005).Hickman ''et al.'' (2003).Houseman (2003).Wischnitzer (1993). For these reasons, the basic directional terms can be considered to be those used in vertebrates. By extension, the same terms are used for many other ( Invertebrate ) organisms as well. Vertebrate directional terms To begin, distinct, polar-opposite ends of the Organism are chosen. By definition, each pair of opposite points defines an axis. In a bilaterally-symmetrical organism, there are 6 polar opposite points, giving three axes that intersect at right angles — the x, y, and z axes familiar from three-dimensional geometry. Anterior and posterior The most obvious end-points are the "nose" and "tail" (see Fig. 2). Anatomically, the nose is referred to as the Anterior End ( Latin ''ante''; before). In organisms like vertebrates, that have distinct heads, the anterior end is sometimes referred to as the '''rostral end''' (Latin ''rostrum''; beak), the '''cranial end''' (Greek ''kranion''; skull), or the '''cephalic end''' ( Greek ''kephalē''; head).Kardong (2005).Hickman ''et al.'' (2003).Wischnitzer (1993). For reasons of broader applicability, especially in organisms without distinct heads (many Invertebrates ), "anterior" is usually preferred.Hickman ''et al.'' (2003).Miller (2002).Ruppert ''et al.'' (2004). The polar opposite to the anterior end is the Posterior End ( Latin ''post''; after). Another term for posterior is '''caudal''' (Latin ''caudum''; tail) — a term which strictly applies only to Vertebrates , and therefore less preferred.Hickman ''et al.'' (2003).Miller (2002).Ruppert ''et al.'' (2004). By drawing a line connecting these two points, we define the anteroposterior axis (sometimes written antero-posterior). Less-used synonyms would be rostrocaudal or cephalocaudal axes (see Table 1). For brevity, the term anteroposterior is often abbreviated to read '''AP''' (or A-P) '''axis'''. As well as defining the anteroposterior axis, the terms "anterior" and "posterior" also define '''relative positions''' along the axis. Thus, in the fish in Fig. 2, the gill openings are ''posterior'' relative ''to'' the eyes, but ''anterior to'' the tail. Dorsal and ventral The next most obvious end-points are the back and belly. These are termed the Dorsal End (Latin ''dorsum''; back) and the ''' Ventral End ''' (Latin ''venter''; Abdomen ), respectively. By connecting the outermost points the '''dorsoventral axis''' is formed (sometimes hyphenated: '''dorso-ventral'''). This is commonly abbreviated to '''DV''' (or D-V) '''axis'''. The DV axis, by definition, is perpendicular (at right angles to) the AP axis at all times (see below). As with anteroposterior, the terms "dorsal" and "ventral" are also used to describe relative positions along the dorsoventral axis. Thus, the Pectoral Fins are ''dorsal to'' the Anal Fin , but ''ventral to'' the Dorsal Fin in Fig. 2. (Note that these fins are not aligned anteroposteriorly, either — the dorsal fin being posterior to the pectoral, and anterior to the anal fins, respectively.) Left and right (lateral), and medial The last axis, by Geometric definition, must be at right angles to both the AP and DV axes. Obviously, the left side and '''right side''' of the organism are the outermost points between the two "sides" of the organism. When connected, these points form the '''left-right axis''' (commonly abbreviated to '''LR''' (or L-R) '''axis'''. Properly, this is called the '''dextro-sinistral''' (or, more uncommonly, the '''sinistro-dextral''') '''axis''', from the Latin '''''dexter''''' (right) and '''''sinister''''' (left). '''It is important to note that the "left" and "right" sides are the sides of ''the organism'', and not those of ''the observer''.''' In practice, and contradictory to the practice with other anatomical terms of location, the Vernacular "left-right" is preferentially used in English and some other languages. This is likely due to the adoption of the Latin " Sinister " to mean "evil" in EnglishBarber (1998). and other languages (''e.g. sinistre'' in French has the same connotationAtkins ''et al.'' (1993).). As with the other directions, the terms can be used as relative terms, to describe locations along the left-right axis. Thus, in Fig. 2 the Dorsal Fin is ''right of'' the left Pectoral Fin , but is ''left of'' the right Eye . However, as left and right sides are Mirror Images , usage like this tends to be somewhat confusing, as structures are duplicated on both sides (''i.e.'' above there is both a right eye and a left eye, forcing one to specify which is used as a reference). To counter this clumsiness of usage, the directional term lateral ( Latin ''lateralis''; "to the side") is used as a modifier for both sides, yielding the '''left lateral''' and '''right lateral''' sides. As an opposite to lateral, the term '''medial''' ( Latin ''medius''; "middle") is used to define a point in the centre of the organism (where the left-right axis intersects the Midsagittal Plane — see below). Thus, rather than "left-right" axis and its inherent clumsiness of usage, the term '''mediolateral''' (also sometimes hyphenated '''medio-lateral''') '''axis''' is frequently used. Sometimes this is abbreviated to '''ML''' (or M-L) '''axis'''.Kardong (2005).Hickman ''et al.'' (2003).Wischnitzer (1993). Properly, the ML axis is a half axis; practically, its usage is less clumsy and less linguistically biased than "left-right". The terms may still be used relatively to describe locations along the LR axis. Thus, in Fig. 2 the Gills are ''medial to'' the Operculum , but ''lateral to'' the Heart . The usage "mediolateral" is strictly used to describe relative position along the left-right axis, to avoid confusion with the terms "superficial" and "deep" (see below). Sources of confusion Vertebrate ''Equus caballus'' (a Horse ). The axis between anterior and posterior is the AP axis, and between the dorsal and ventral is the D-V axis. (Left-right axis not shown; image shows the right side of the organism.)]] Together, the AP, DV and LR (or ML) axes allow for precise three-dimensional descriptions of location within any Bilaterally-symmetrical organism, whether Vertebrate or Invertebrate . In practice, the terms can cause some confusion when, unlike the fish shown in Fig. 2, the organism in question is not strictly linear in form (see Figs. 3 and 4). For example, the AP axis in Fig. 3 does not appear to be at right angles to the DV axis. Rather, it is a depiction of the approximate average AP axis, when all body segments are included. ). Axis (A) (in red) shows the AP axis of the tail, (B) shows the AP axis of the neck, and (C) shows the AP axis of the head.]] When considering ''any one segment'', the dorsoventral axis is perpendicular to the AP axis. Thus, in Fig. 4, the DV axis of the tail would run from the "back" of the tail (posterior end of the trunk), to the "underside" of the tail (near the legs) — nearly parallel to the AP axis of the main body. As a general rule of thumb, if the body is included in consideration, the AP axis of the main body would be used, as would the DV and ML axes perpendicular to it. However, if considering ''only'' one segment, the AP axis would shift to reflect the axes shown in Fig. 4, with the DV and ML axes shifting correspondingly. Alternatively, to avoid confusion, AP, DV and ML terms are used ''strictly'' in relation to the main body, and the terms proximal and distal are used for body segments such as the head, neck and tail (see below). Proximal and distal The term proximal ( Latin ''proximus''; nearest) is used to describe where the appendage joins the body, and the term '''distal''' (Latin ''distare''; to stand away from) is used for the point furthest from the point of attachment to the body. Since Appendages often move independently of (and therefore change position with respect to) the main body, these separate directional terms are used when describing them. As noted above, the standard AP, DV and ML directional axes, can cause some confusion when describing parts of the body that can change position (move) relative to the main body. This is particularly true when considering Appendages . "Appendages" would include Vertebrate Fins (see Fig. 2) and Limbs (see Figs. 3 and 4), but properly apply to any structure that extends (and can at least potentially move separately) from the main body. Thus, "appendage" would also include such structures as external Ears ( Pinneae ) and Hair (in Mammals ), Feathers (in Birds ) and Scales ( Fish , Reptiles and birds). As well, varieties of Tentacles or and other projections from the body in Invertebrates and the male Penis in many vertebrates and some invertebrates, would be included. By connecting the two points, the proximodistal (sometimes hyphenated to '''proximo-distal''') '''axis'''. (The abbreviation '''AB axis''' is occasionally, but not commonly, used.) As before, the terms "proximal" and "distal" can be used as relative terms to indicate where structures lie along the proximodistal axis. Thus, the "elbow" is proximal to the hoof, but distal to the "shoulder" in Figs. 3 and 4. Choosing terms for the other two axes perpendicular to the proximodistal axis could be variable, as they would also depend on the position of the limb. For that reason, when considering any organism, the other two axes are considered to be relative to the appendage when in standard anatomical position. This is roughly defined for all organisms, as in the normal position when at rest and not moving. For Tetrapod Vertebrates , this includes the caveat that they are standing erect and not lying down. Thus, the fish in Fig. 2, and the horse in Figs. 3 and 4 are in standard anatomical position. (Special considerations with respect to limb position are applied in human anatomy — see below). Other directional terms In addition to the three primary axes (AP, DV and the ML half-axis) and the proximodistal axis of appendages, several directional terms can be used in Bilaterally Symmetrical animals. These terms are strictly relative, and as such ''do not and cannot be used to define fixed axes''. These terms include:
Invertebrate directional terms The large variety of Body Shapes present in invertebrates presents a difficult problem when attempting to apply standard directional terms. Depending on the organism, some terms are taken by analogy from the vertebrate terms, and appropriate novel terms are applied, as necessary. In all cases, the usage of terms is dependent on the Bauplan of the organism. . (a) An organism with an asymmetrical bauplan (''Amoeba proteus'' — an amoeba). (b) An organism with a spherical bauplan (''Actinophrys sol'' — a Heliozoan .]] Asymmetrical and Spherical organisms In organisms with a changeable shape, such as Amoeboid organisms (Fig. 5a), directional terms are meaningless, since the shape of the organism is changeable, and no fixed axes are present. Similarly, in organisms that are Spherical in shape (Fig. 5b), there is nothing to distinguish one line through the centre of the organism from another. An infinite number of triads of mutually perpendicular axes could be defined, but any such choice of axes would be functionally and practically indistinguishable from all others, and therefore would be useless. In such organisms, only the terms ''superficial'' and ''deep'' hold any descriptive meaning. 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, like that pictured in Fig. 6, are Planktonic (free-swimming) Protists , 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 or other unique structure is present.Ruppert ''et al.'' (2004). Elongated organisms with distinctive ends Some elongated Protists have distinctive ends of the body. 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 opposite the Flagellum in '' Euglena ''), is normally designated as the anterior end. The opposite end then becomes the '''posterior end''', and by connecting them, an '''anteroposterior axis''' is formed.Ruppert ''et al.'' (2004). Properly, this terminology would only apply to an organism that is always Planktonic (not normally attached to a surface — as in Fig. 6 top), although the term can also be applied to one that is Sessile (normally attached to a surface — as in Fig. 6, bottom and Fig. 7). Organisms that are attached to a Substrate , such as Sponges (Fig. 7), or some Animal-like Protists also have distinctive ends. The part of the organism attached to the substrate is usually referred to as the basal end ( Latin ''basis''; support or foundation), whereas the end furthest from the attachment is referred to as the '''apical end''' (Latin ''apex''; peak, tip). Thus, by joining the two ends, an '''apical-basal''' (or '''basal-apical''') '''axis''' is formed (see Fig. 7). '''Transverse axes''' may be defined indifferently in any direction perpendicular to this axis, as there is no symmetry present. Radially-symmetrical organisms Radially Symmetrical Organisms include those in the group Radiata — primarily Jellyfish, Sea Anemones And Corals and the Comb Jellies .Hickman ''et al.'' (2003).Ruppert ''et al.'' (2004). Adult Echinoderms (sea stars (starfish), sea urchins, and sea cucumbers and others) are also included, since they are pentaradial (''i.e.'' they have five-fold Discrete Rotational Symmetry ). Echinoderm Larvae are ''not'' included, since they are Bilaterally Symmetrical .Hickman ''et al.'' (2003).Ruppert ''et al.'' (2004). ), showing the oral-aboral, and proximodistal axes. (Note that the Appendages are not in standard anatomical position, so that the axis is curved.)]] Unlike spherical and asymmetrical organisms, radially-symmetrical animals always have one distinctive axis. , showing multiple radial and medio-peripheral axes.]] Cnidarians 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).Ruppert ''et al.'' (2004). For this reason, the end of the organism with the mouth is referred to as the oral end ( Latin ''oris''; mouth), and the opposite surface is the '''aboral end''' (Latin ''ab-''; prefix meaning "away from"). Thus, by joining the polar opposite oral and aboral ends, an '''oral-aboral axis''' is formed (Fig. 8). As with vertebrates, Appendages that move independently of the body ( Tentacles in Cnidarians and Comb Jellies ), have a definite proximodistal axis (Fig. 8). Unlike vertebrates, cnidarians (jellyfish, sea anemones, corals) have no other distinctive axes, and multiple '''radial axes''' are possible (Fig. 9). It is noteworthy that some "biradially-symmetrical" Comb Jellies have distinct "tentacular" and "'''pharyngeal'''" axes,Ruppert ''et al.'' (2004), ''p.'' 184. and are thus anatomically equivalent to Bilaterally-symmetrical animals. As well, adult Echinoderms (starfish, sea urchins, sea cucumbers) are ''pentaradial'', and have only five symmetrical radial axes (unlike the multiple axes in cnidarians). "Lateral", '''dorsal''', and '''ventral''' have no meaning in such organisms, and all can be replaced by the generic term '''peripheral''' (Latin ''peri-''; around; see Table 2). '''Medial''' can be used, but in the case of radiates indicates the central ''point'' of these organisms, rather than a central ''axis'' (as in vertebrates). Thus, as there are many possible radial axes, there are multiple '''medio-peripheral''' (half-) '''axes''' (Fig. 9). Medical (human) directional terms As we are Bilaterally-symmetrical organisms, anatomical directions in Humans can correctly be described using the same terms as those for vertebrates and other members of the taxonomic group Bilateria . However, for historical and other reasons, standard human directional terminology has several differences from that used for other bilaterally-symmetrical organisms. Why zootomy and human anatomy terms differ Although it can be argued that the standard directional nomenclature used for vertebrate zootomy can and should be used for Medical Anatomy , the differences persist. The differences in terminology arose (and are perpetuated) for three primary reasons:
Unfortunately, the persistence of medical terminology as distinct from that used for other vertebrates tends to be confusing. For a quick comparison of equivalent terminology used in vertebrate and human anatomy, see Table 3 (below). Superior and inferior As with other vertebrates, two of the most obvious extremes are the "top" and the "bottom" of the organism. In standard anatomical position, these correspond to the head and feet, respectively in humans. The head end is referred to as the superior end ( Latin ''superior'': "above"), while the feet are referred to as the '''inferior end''' (Latin ''inferior'': "below"). Thus, the axis formed by joining the two is the '''superior-inferior axis'''.Marieb (1995)Tortora and Derrickson (2006) As in other vertebrates, there are synonymous terms for superior and inferior (Table 3). The terms cranial, '''cephalic''', and '''rostral''' are occasionally encountered. "Cranial", as a reference to the skull, is fairly commonly used, whereas "cephalic" is uncommonly used, and "rostral" is rarely used in human anatomy.Tortora and Derrickson (2006), ''p.'' 14. Similarly, the term '''caudal''' is occasionally used in human anatomy,Tortora and Derrickson (2006), ''p.'' 14. and the '''cranio-caudal axis''' is occasionally encountered. Generally, this usage would only be used with respect to the head and main body (trunk), and not when considering the limbs. As with vertebrate directional terms, superior and inferior can be used in a relative sense. For example, the Shoulders are ''superior to'' the Navel , but ''inferior to'' the Eyes . Anterior and posterior Anterior and '''posterior''', as used in medical/human anatomical descriptions are major sources of confusion to those accustomed to standard vertebrate directional terminology, and ''vice versa''. The confusion arises from the differences in '''standard anatomical positions''' of Quadruped vertebrates and Bipedal humans. In human anatomical usage, anterior refers to the "front" of the individual, and is ''synonymous with '''ventral'''''. Similarly, '''posterior''', in medical anatomy refers to the "back" of the subject, and is ''synonymous with '''dorsal''''' (see Table 3).Tortora and Derrickson (2006) ''p.'' 14. The terms "dorsal" and "ventral" are used in human anatomy, but infrequently when referring to the body as a whole.The term "dorsal" is used with respect to limb position, however. Thus, the '''anteroposterior axis''' is preferred usage for describing the axis connecting the front and the back in humans.Marieb (1995) ''p.'' 16Tortora and Derrickson (2006) ''p.'' 14. As in other vertebrates, "anterior" and "posterior" can also be used as relative terms. Thus, the Eyes are ''posterior to'' the Nose , but ''anterior to'' the back of the head. Left and right (lateral), and medial Left and right lateral are used in the same sense as they are in other vertebrates, as is '''medial'''. The '''left-right axis''' is rarely used in medicine, however; the '''mediolateral axis''' is used almost exclusively.Marieb (1995), ''p.'' 16.Tortora and Derrickson (2006), ''p.'' 14. Appendages As in other vertebrates, the terms "proximal" and "'''distal'''" are used to describe the point of attachment to, and part of an appendage furthest away from, the body, respectively. However, other terms are used for direction in the appendages, given the unique position of the limbs (in standard anatomical position) in humans. =Arms In standard anatomical position, the palms of the hands point anteriorly. Thus, anterior can be (and sometimes is) used to describe the Palm of the hand, and '''posterior''' can be (and sometimes is) used to describe the back of the hand and arm. However, presumably for improved clarity, the directional term palmar ( Latin ''palma''; palm of the hand) is usually used for the anterior of the hand, and '''dorsal''' is used to describe the back of the hand. Thus, by connecting the extremes, '''dorsopalmar axis''' is formed. Most commonly, "dorsopalmar" is used when describing the hand, although it is sometimes applied to the arm as a whole (see Fig. 11). For the third axis, the mediolateral axis suffices, although if referring to the limb alone, "medial" may refer to the centre of the arm itself. RELATIVE DIRECTIONS Also, in common usage, the segments of the Digestive System closest to the Mouth are termed proximal, as opposed to those closest to the Anus , which are termed '''distal'''. Relative directions in the limbs Specialized terms are used to describe location on appendages, parts that have a point of attachment to the main trunk of the body. Structures that are close to the point of attachment of the body are proximal or '''central''', while ones more distant from the attachment point are '''distal''' or '''peripheral'''. For example, the hands are at the distal end of the arms, while the shoulders are at the proximal ends. These terms can also be used relatively to organs, for example the proximal end of the Urethra is attached to the Bladder . In the limbs of most animals, the terms cranial and '''caudal''' are used in the regions proximal to the carpus (the Wrist , in the forelimb) and the tarsus (the Ankle in the hindlimb). Objects and surfaces closer to or facing towards the head are ''cranial''; those facing away or further from the head are ''caudal''. Nearer the carpal joint, the term dorsal replaces '''cranial''' and '''palmar''' replaces '''caudal'''. Similarly, nearer the tarsal joint the term dorsal replaces '''cranial''' and '''plantar''' replaces '''caudal'''. 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. The sides of the forearm are named after its bones: 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'''. Similarly, in the lower leg, structures near the Tibia (shinbone) are '''tibial''' and structures near the Fibula are '''fibular''' (or '''peroneal'''). Volar (sometimes used as a synonym for "palmar") refers to the underside, for both the palm and the sole (''plantar''), as in '''volar pads''' on the underside of hands, fingers, feet and toes. The terms Valgus and Varus are used to refer to angulation of the distal part of a limb at a joint. For example, at the Elbow joint, in the anatomical position, the forearm and the upper arm do not lie in a straight line, but the forearm is angulated laterally with respect to the upper arm by about 5–10°. The forearm is said to be "in valgus". Angulation at a joint may be normal (as in the elbow) or abnormal. PLANES General usage Three basic reference planes are used in zoological anatomy.
For post- Embryo humans a Coronal Plane is vertical and a transverse plane is horizontal, but for embryos and quadrupeds a coronal plane is horizontal and a transverse plane is vertical. When describing anatomical motion, these planes describe the axis along which an action is performed. So by moving through the transverse plane, movement travels from head to toe. For example, if a person jumped directly up and then down, their body would be moving in the transverse plane. Some of these terms come from Latin. ''Sagittal'' means "like an arrow", a reference to the position of the spine which naturally divides the body into right and left equal halves, the exact meaning of the term "midsagittal". A ''longitudinal plane'' is any plane perpendicular to the transverse plane. The Coronal Plane and the Sagittal Plane are examples of longitudinal planes. Usage in human anatomy Sometimes the orientation of certain planes needs to be distinguished, for instance in Medical Imaging techniques such as Sonography , CT Scans , MRI Scans or PET Scans . One imagines a human in the anatomical position, and an X-Y-Z Coordinate System with the X-axis going from front to back, the Y-axis going from left to right, and the Z-axis going from up to down. The X-axis axis is always forward ( Tait-Bryan Angles ) and the Right-hand Rule applies.
The axes and the sagittal plane are the same for bipeds and quadrupeds, but the orientation of the coronal and transverse planes switch. The axes on particular pieces of equipment may or may not correspond to axes of the body, especially since the body and the equipment may be in different relative orientations. Occasionally, in medicine, Abdominal organs may be described with reference to the trans-pyloric plane which is a transverse plane passing through the Pylorus . Anatomical planes in animal brains In discussing the Neuroanatomy of animals, particularly Rodent s used in Neuroscience research, the convention has been to name the sections of the brain according to the homologous human sections. Hence, what is technically a ''transverse'' section with respect to the body of a rat (dividing anterior from posterior) may often be referred to in rat neuroanatomical coordinates as a ''coronal'' section, and likewise a ''coronal'' section with respect to the body (ie. dividing ventral from dorsal) in a rat brain is referred to as ''transverse''. This preserves the comparison with the human brain which is rotated with respect to the body axis by 90 degrees in the ventral direction. It does mean that the planes of the rat brain are not necessarily the same as those of the body. Surface and other landmarks in humans In humans, reference may be made to landmarks which are on the skin or visible underneath. As with planes, lines and points are imaginary. Examples include:
Additionally, reference may be made to structures at specific levels of the Spine (e.g. the 4th Cervical Vertebra , abbreviated "C4"), or the rib cage (e.g. the 5th Intercostal Space , abbreviated "5ICS"). RELATIVE MOTIONS See Also: Anatomical terms of motion NOTES REFERENCES
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