The “x”, “y”, and “z” axes of the Cartesian coordinate system and the corresponding three “cardinal planes” (or “Cartesian planes”) (“xy” plane, “yz” plane, “zx” plane) are used in anatomy and kinesiology to specify the locations and movements of body-parts. The three Cartesian axes (ie. dimensions) and three cardinal planes have been referred to with various terms. These may create confusion because the same term might describe different planes and also a dimension (eg. “vertical” see below).

Center of planes

In some places a “cardinal plane” indicates that the planes are passing through the body’s centre of gravity, when they do not pass through the body’s centre or gravity then they are specified by the location of the three planes central intersection point (eg. shoulder centred cardinal planes) (Rasch and Burke, 1978, pp. 97–98; Wells and Luttgens, 1976, p. 20). Conceptually, for analysis, the center of the three cardinal planes can be placed anywhere inside of the body (egocentric), or outside (exocentric). In practice the question of center may be based on actual body movement organisation, initiation, etc.


Median plane, Sagittal plane

The human body and the bodies of many animals display reflection symmetry between their right and left sides. A plane can be imagined which passes through the centre of the body and exactly divides the right side from the left.

Terms: The “median plane” (1) and “sagittal plane” (2) seem to be used synonymously as dividing a “bilaterally symmetrical animal into right and left halves” (American, 1982). Within choreutics the term “wheel plane” is often used since this plane has the same orientation as a wheel. (3)

Sometimes a distinction is made depending if the plane passes through the body center, with the median plane considered to pass through the body centre while the sagittal plane as “dividing the body into unequal left and right parts and parallel to the median plane” (Kapit and Elson, 1977, p. 1 [italics mine]).

The difference in location of center leads to more specifications for concepts for a sagittal plane also passing through center:

• “midline plane” (Dempster, 1955, p. 581),
  
• “median sagittal plane” (Craske and Crawshaw, 1974b, p. 274),
  
• “mid-sagittal plane” (Dempster, 1955, p. 563; Dempster et al., 1959, p. 296; Howard, 1986, p. 3)
  

• a statistical average,
  
• a dividing strip between opposing directions of traffic,
  
• a verb (mediate) to intervene and negotiate between conflicting parties to bring an agreement,
  
• in any reference of something being towards the middle (American, 1982; Collins, 1986).
  

• the sagittal suture (the joint between the two parietal bones lying on a forward/backward line across the top of the skull)
  
• in reference to anything parallel to the sagittal suture (American, 1982; Collins, 1986).
  

• Sagittal is most specific to the forward/backward dimension, also closest to the Latin root of an arrow.
  
  
• Median is most specific to a plane and stresses the right-left division (rather than prioritising either the vertical or the sagittal components).
  

• the ring visible around the sun or moon when they are viewed through a thin mist,
  
• the upper part of the head or coronal suture,
  
• a circle of light or halo,
  
• the coronary arteries which entirely encircle the heart,
  
• a garland, wreath, circlet, or crown as used in a coronation (American, 1982; Collins, 1986).
  

• the frontal bone of the skull,
  
• the frontal lobe of the cerebral cortex (under the frontal bone),
  
• a forehead ornament,
  
• a frontal view in visual arts,
  
• the facade or front of a building (American, 1982; Collins, 1986).
  

• being at a right angle to the horizon,
  
• upright,
  
• the highest point,
  
• directly overhead (American, 1982).
  

• anything relating to the sides,
  
• curling the tongue so that the air stream passes around its sides (eg. making the sound “L”),
  
• solving problems by employing unorthodox or seemingly illogical means,
  
• throwing the ball sideways in American football,
  
• the difference between the right and left cerebral hemispheres (American, 1982; Collins, 1986).
  

• Vertical is most specific to the upward/downward dimension, also closest to the Latin root ‘vertex’
  
  
• Frontal is most specific to a plane stressing the surface of the plane separating in front from behind (rather than prioritising either the vertical or the lateral components of the plane).
  

• where the earth and the sky visually appear to intersect,
  
• the range of a person’s knowledge experience or interest,
  
• occupying the same level in a hierarchy,
  
• uniformity or equality to all members of a group,
  
• a layer in soil or rock which has a particular composition,
  
• level, anything parallel to the plane of the horizon (American, 1982; Collins, 1986).
  

• a line that intersects two or more other lines,
  
• crossing from sided to side,
  
• a transverse process (a sideward projection extending from either side of a vertebra),
  
• the transverse colon (part of large intestine running sidewards around front of abdomen),
  
• the way a flute is held at right angles to the mouth,
  
• anything lying across or crosswise (American, 1982; Collins, 1986).
  

• Lateral is most specific to the rightward/leftward dimension, also closest to the Latin root of sideways.
  
  
• Horizontal is most specific to a plane and stresses the circular surface perpendicular to the vertical and separating above from below (rather than prioritising either the lateral or the sagittal components of the plane).