Oral-aboral axis ( Schulze, 1893 ) : Synonym for rostrocaudal axis; often preferred in the comparative anatomy of invertebrates; p. 5. Also see Willmer (1990, p. 15).

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Anteroposterior axis ( Swanson & Bota, 2010 ) : Often used as synonym for rostrocaudal axis in most vertebrates and for the dorsoventral axis in humans; see Standring (2008, Fig. 1). Application of this old and confusing designation is discouraged; see anterior (Aristotle) and anterior (Galen, c177). Also spelled anterior-posterior axis.

Longitudinal axis ( Barclay, 1803 ) : The oral-aboral axis (Schulze, 1893) of the body in all animals with a nervous system (Monro, 1783); term probably introduced by Barclay (1803, p. 117); also see Henle (1855, p. 1), Willmer (1990, p. 15). Other synonyms include rostrocaudal axis, central axis, long axis, midsagittal axis, principal axis, and anteroposterior axis, the latter being discouraged as especially ambiguous in comparative anatomy. The longitudinal axis is orthogonal to the transverse axis (Henle, 1855). The concept was clearly described by Aristotle in De Partibus Animalium, where he wrote that "a straight line as an axis has at the upper end the mouth, followed by the gullet, stomach, intestine, and excremental vent"; and that furthermore in some animals like humans, quadrupeds, crustacea, and insects the axis is essentially straight, whereas at the other extreme in animals like the Cephalopods it can be highly curved and thus U-shaped; see translation by Ogle (1912, 685a-686b). Kuhlenbeck (1973, p. 111) provided a nice modern statement of the concept: "Three so-called "axial lines" [longitudinal or rostrocaudal, dorsoventral, and mediolateral] which can be conceived as geodesics and therefore not necessarily ‘straight', provides an essentially nonmetric and non-Euclidean (Euclidoid), ameboid three-dimensional coordinate system (German: "Bezungsmollusk") of anatomical space…"

Rostrocaudal axis : Equally acceptable synonym for longitudinal axis (Barclay, 1803), but also indicating polarity or direction toward the oral (Schulze, 1893) or rostral (Schulze, 1893) end, or toward the aboral (Schulze, 1893) or caudal (Cleland, 1879) end, of the axis; see oral-aboral axis (Schulze, 1893); used recently by for example Kuhlenbeck (1973, p. 111), Nauta & Feirtag (1986, pp. 39-40) and Swanson (2003, pp. 223-228).