| principal plane | <microscopy> A plane normal to the principal axis of a lens, passing through a principal point. In geometrical construction of ray diagrams through a perfect lens, the single plane that can be considered (disregarding the refraction of the rays at each optical interface) to convert paraxial rays into rays converging onto the rear focal point. For thin symmetrical lenses, there is one principal plane that bisects the lens. For thick or complex lenses, there is a principal plane for the paraxial ray to the left, and another for the paraxial ray to the right, of the lens. (05 Aug 1998) |
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| second parallel pelvic plane | The plane extending from the middle of the posterior surface of the pubic symphysis to the junction of the second and third sacral vertebrae, and laterally passing through the ischial bones over the middle of the acetabulum. Synonym: second parallel pelvic plane, wide plane. (05 Mar 2000) |
| horizontal plane | A plane across the body at right angles to the coronal and sagittal plane's. Synonym: horizontal plane. (05 Mar 2000) |
| spectacle plane | The plane at which spectacles are worn. (05 Mar 2000) |
| nasion-postcondylar plane | A plane passing through the nasion anteriorly and to a point immediately behind each condylar process of the mandible, posteriorly. (05 Mar 2000) |
| sternal plane | A plane indicated by the front surface of the sternum. Synonym: planum sternale. (05 Mar 2000) |
| subcostal plane | A horizontal plane passing through the inferior limits of the costal margin, i.e., the tenth costal cartilages; it marks the boundary between the hypochondriac and epigastric regions superiorly and the lateral and umbilical regions inferiorly. Synonym: planum subcostale, infracostal line. (05 Mar 2000) |
| nodal plane | The plane corresponding to the optical centre of a simple lens. See: nodal point. (05 Mar 2000) |
| nuchal plane | <anatomy> The external surface of the squamous part of the occipital bone below the superior nuchal line, giving attachment to the muscles of the back of the neck. (05 Mar 2000) |
| datum plane | An arbitrary plane used as a base from which to make craniometric measurements. (05 Mar 2000) |
| Daubenton's plane | The plane of the foramen magnum. See: Daubenton's angle, Daubenton's line. (05 Mar 2000) |
| supracrestal plane | A horizontal plane passing through the summits of the iliac crests; it usually passes through the fourth lumbar spinous process. Synonym: planum supracristale, supracrestal plane. (05 Mar 2000) |
| supracristal plane | A horizontal plane passing through the summits of the iliac crests; it usually passes through the fourth lumbar spinous process. Synonym: planum supracristale, supracrestal plane. (05 Mar 2000) |
| supraorbitomeatal plane | A plane passing the superior orbital margins and the superior margin of the external acoustic meatuses; it makes an angle of approximately 25 to 30 degrees with the Frankfort plane and is the plane in which routine CT (computed tomography) scans of the brain are made. (05 Mar 2000) |
| suprasternal plane | A horizontal plane passing through the body at the level of the superior margin of the manubrium of the sternum. (05 Mar 2000) |