Standard anatomical position

Because animals can change orientation with respect to their environment, and because appendages (arms, legs, tentacles, etc.) can change position with respect to the main body, it is important that anatomical terms of location refer to the organism when it is in its standard anatomical position.

Thus, all descriptions are with respect to the organism in its standard anatomical position, even when the organism in question has appendages in another 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.

Standard anatomical position is rigidly defined for human anatomy. In standard anatomical position, the human body is standing erect and at rest. Unlike the situation in other vertebrates, the limbs are placed in positions reminiscent of the supine position imposed on 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. The positions of the limbs (and the arms in particular) have important implications for directional terms in those appendages. The penis in the anatomical position is detached and laid next to the body such that the dorsal surface of the penis is actually the anterior surface when the penis is pointing down between the legs.

In humans, the anatomical position of the skull has been agreed by international convention to be the Frankfurt plane or Frankfort plane, a position in which the lower margins of the orbits, the orbitales, and the upper margins of the ear canals, the poria, all lie in the same horizontal plane. This is a good approximation to the position in which the skull would be if the subject were standing upright and facing forward normally.

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