Anatomical Terms of Location - Directional Terms - Medical (human) Directional Terms - Why Zootomy and Androtomy Terms Differ

Why Zootomy and Androtomy Terms Differ

The terms of zootomy and androtomy came into usage at a time when all scientific communication took place in Latin. In their original Latin forms the respective meanings of "anterior" and "posterior" are in front of (or before) and behind (or after), those of "dorsal" and "ventral" are toward the spine and toward the belly, and those of "superior" and "inferior" are above and below. From these meanings it can be seen that in the most general terms the anterior/posterior axis is oriented to the direction of forward motion, the dorsal/ventral axis is oriented to the anatomy of the vertebrate torso, and the superior/inferior axis is oriented to gravity.

For almost all vertebrates, including almost all bipeds, these axes all provide a consistent reference for anatomical positions across species—with the inferior/superior axis being roughly the same as the dorsal/ventral axis, and therefore redundant. Humans, however, have the rare property of having a torso oriented perpendicular to their direction of forward motion—while their head orientation remains consistent with other vertebrates on this axis. This makes the dorsal/ventral axis on humans redundant with the anterior/posterior axis, and the inferior/superior axis necessary. Because of this difference with humans, the anterior/posterior and inferior/superior axes are inconsistent between humans and other vertebrates in torso anatomy but consistent in head anatomy. As all three of these axes are used in the naming of anatomical structures, and most human anatomical structures are shared by other animals, these differences can lead to considerable confusion. For example, in the naming of brain structures, the non-human context of the dorsal/ventral axis was used. Therefore, in human anatomy, "dorsal" can refer to two different (perpendicular) directions—the posterior direction in the context of the torso, and the superior direction in the context of the brain. Ironically, the "dorsal" direction in the human brain, besides being perpendicular to the "dorsal" direction in the human torso, is actually the opposite direction of what might be inferred from the literal Latin meaning of "toward the spine".

While it would be possible to introduce a system of axes that is completely consistent between humans and other vertebrates by having two separate pairs of axes, one used exclusively for the head (e.g. anterior/posterior and inferior/superior) and the other exclusively for the torso (e.g. dorsal/ventral and caudal("toward the tail")/rostral("toward the beak")), doing so would require the renaming of very many anatomical structures.

For a quick comparison of equivalent terminology used in vertebrate and human anatomy, see Table 3 (below).

Table 3: Equivalent directional terms used in
vertebrate zoology and human anatomy
Vertebrate zootomy Human torso Human head
Direction Synonyms Direction Synonyms Direction Synonyms
Anterior Rostral, Cranial, Cephalic1 Superior Same1, Up Anterior Rostral, Front
Posterior Caudal Inferior Caudal1, Down Posterior Caudal, Back
Dorsal Posterior Dorsal, Back Superior Dorsal, Up
Ventral Anterior Ventral, Front Inferior Ventral, Down
lateral Away from the middle Same Same
Left (lateral) Sinister1 Same Same
Right (lateral) Dexter1 Same Same
Medial Middle Same Same
Proximal Away from extremity Same Same
Distal Toward extremity Same Same
Intermediate2 Same Same
Ipsilateral2 Same side Same Same
Contralateral2 Opposite side Same Same
Superficial2 Same Same
Deep2 Same Same
Notes:
(1) Rarely used.
(2) Strictly relative term, used with other locational descriptors.

Read more about this topic:  Anatomical Terms Of Location, Directional Terms, Medical (human) Directional Terms

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