APPENDIX VIII
TERMINOLOGY FOR CARTESIAN DIMENSIONS AND PLANES

The “x”, “y”, and “z” axes of the Cartesian coordinate system and the corresponding three “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 Cartesian 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). These terms will be briefly reviewed and terms used in this research will be designated.

When the Cartesian planes are conceived to pass through the body’s centre of gravity then they are termed the “cardinal” planes. 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 Cartesian planes) (Rasch and Burke, 1978, pp. 97–98; Wells and Luttgens, 1976, p. 20). Thus, each Cartesian plane might be described as passing through the centre of gravity, or as parallel to a central plane.

The human body and the bodies of many animals, display a 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. The terms “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). Sometimes the term “midline plane” (Dempster, 1955, p. 581), “median sagittal plane” (Craske and Crawshaw, 1974b, p. 274), or “anteroposterior” plane (Wells and Luttgens, 1976, p. 20) are used. In other places the median plane is considered to pass through the centre while the sagittal plane is described as “dividing the body into unequal left and right parts and parallel to the median plane” (Kapit and Elson, 1977, p. 1 [italics mine]). Thus, a “mid-sagittal plane” (Dempster, 1955, p. 563; Dempster et al., 1959, p. 296; Howard, 1986, p. 3) would specify a sagittal plane passing through centre. In other places the sagittal plane is considered to either pass through centre or not (eg. Fitt, 1988, p. 21). Because it contains an up/down component this plane can also be referred to as a “vertical plane” (American, 1982; Barnes, 1963, pp. 260-261; Bodmer, 1979, p. 13; Schmidt and McGown, 1980, p. 155; Wells and Luttgens, 1976, p. 20). Within choreutics the term “wheel plane” is often used since this plane has the same orientation as a wheel. (3)

The term “median” comes from the Latin for “middle” and is used in English to refer to (for example) a statistical average, a dividing strip between opposing directions of traffic, as a verb (mediate) to refer to intervening and negotiating differences between conflicting parties to bring an agreement, or in any general reference of something being towards the middle (American, 1982; Collins, 1986).

The term “sagittal” comes from the Latin for “arrow” and is used in anatomy to refer to the sagittal suture (the joint between the two parietal bones lying on a forward/backward line across the top of the skull) or in reference to anything parallel to the sagittal suture (American, 1982; Collins, 1986).

The term “sagittal” is also commonly used to refer to the forward/backward dimension. (4) When sagittal is considered to be a plane, then the dimension is sometimes referred to as the “sagittal horizontal axis” (Wells and Luttgens, 1976, p. 39).

The term “sagittal” will be used here only to refer to the forward/backward dimension. This is also closest to the Latin root of sagittal as an arrow. The term “median” will be used to refer to the plane. In the case of a non-central plane the term “paramedian” (ie. parallel to the median plane) can be used. The term “wheel plane” is descriptive but the idea of a wheel may introduce a bias towards the sagittal dimension at the expense of the up/down component of the plane.

Another plane separates the front of the body from the back. This plane is usually referred to as either the “frontal plane” (5) or the “coronal plane”. (6) Howard (1986, p. 3) refers to the “mid-frontal plane” as equivalent with the “coronal plane”, thus implying that the frontal plane does not necessarily pass through centre. Because of the up/down component this plane is sometimes referred to as a “vertical plane” (Dell, 1970, p. 73; 1972, p. 7; Wells and Luttgens, 1976, p. 20) and because of the right/left component it is sometimes referred to as a “lateral plane” (Fitt, 1988, p. 22; Wells and Luttgens, 1976, p. 20). In choreutics this plane is often referred to as the “door plane” (7) since it is parallel to the orientation of a closed door.

The term “coronal” comes from the Latin for “crown” and is used in English to refer to (for example) 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 which might be used in a coronation (American, 1982, Collins, 1986).

The term “frontal” comes from the Latin for “facade” (American, 1982) and “forehead” (Collins, 1986) and is used in English to refer to (for example) 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 of a building, or an ornamental drapery over the front of an alter.

The term “vertical” comes from the Latin for “vertex” and is used in English to refer to being at a right angle to the horizon, upright, the highest point, and directly overhead. A “vertical circle” is defined as a circle which “passes through the zenith and the nadir and thus is perpendicular to the horizon (American, 1982). The idea of a vertex enforces how this term is primarily used to refer to the up/down dimension.

The term “lateral” comes from the Latin for “side” and is used in English to refer to (for example) 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, and the difference between the right and left cerebral hemispheres (American, 1982; Collins, 1986).

Both the frontal and the horizontal plane contain laterality, and so sometimes the right/left dimension is referred to as the “frontal horizontal axis” (Wells and Luttgens, 1976, p. 39). The term lateral may be best suited to refer to the right/left dimension.

The terms “vertical” and “lateral” will be used here to refer to dimensions (Cartesian axes). The term “frontal” appears to be more appropriate for this plane since the Latin root for “coronal” describes the circular shape of a crown rather than a planar orientation. In cases where the plane specifically passes through the centre the term “midfrontal” can be used.

The other Cartesian plane perpendicular to the vertical dimension is typically referred to as the “horizontal plane” (8) or the “transverse plane” (9), though sometimes “longitudinal” plane is used (Saltzman, 1979, p. 95). In choreutics this plane is often termed the “table plane” (10). Howard (1986, p. 3) implies that the transverse plane is not necessarily central and so the term “mid-transverse plane” is used to specify the central plane. In other places a “transverse plane” refers to any plane that cuts cross-ways through the long axis of the body but not necessarily oriented horizontally (Kapit and Elson, 1977, p.1).

The term “horizontal” comes from a Greek term for the boundary of a circle. The terms “horizon” and “horizontal” are used in English to refer to (for example) 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, or anything parallel to the plane of the horizon (American, 1982; Collins, 1986).

“Transverse” comes from the Latin “to turn or direct across” and is used in English to refer to (for example) 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 the large intestine which runs sidewards around the front of the abdomen), the way a flute is held at right angles to the mouth, or anything which is lying across or crosswise (American, 1982; Collins, 1986).

“Transverse” is also used in choreutics to refer to lines which cut across other lines. This notion of “cutting across” appears to be the essence of the term and it is used this way in geometry. Thus, this term will not be used here to refer to a plane.

The term “horizontal” will be used to refer to the plane and this seems close to its Latin root as the boundary of a circle. When the horizontal plane needs to be specified as passing through the centre, the term “midhorizontal” can be used. The term “table plane” elicits a vivid image but it creates an association of a plane at table-level whereas a horizontal plane could be on the floor, or high above the head.

The term “horizontal” is also used to refer to the right/left dimension (11). This usage may have developed since when viewed from the front the horizontal plane is seen as a right/left line, thus, the horizontal dimension. However, any line perpendicular to the vertical (eg. the sagittal dimension or any other line in the horizontal plane) can be described as a “horizontal” line (12). To avoid confusions the term “lateral” is used here to refer to the right/left dimension.

SUMMARY:
In this research the following terms for Cartesian axes (dimensions) and Cartesian planes will be used:

PLANES
Medial	(or paramedial for a non-central plane)
Frontal	(or midfrontal for a central plane)
Horizontal	(or midhorizontal for a central plane)
DIMENSIONS:
Vertical	(gravity up/down or anatomical superior/inferior)
Sagittal	(anatomical anterior/posterior)
Lateral	(anatomical right/left)